Apes aren’t the only primates to use tools

5 10 2007


A chimpanzee cracking open nuts placed on the ground with a large stone. Notice that a young chimpanzee is also present, learning this behavior. This is a sort of Type 1 tool use where a hammer (the rock) is used on another object.

“Tool use” was once considered one of the primary factors that made Homo sapiens distinct from all other animals, but Jane Goodall’s studies of Chimpanzees at Gombe and subsequent research among living apes has shown that the tool use of humans is differentiation of grade and complexity more than anything else. Tool use has now been extended to many other groups of animals, even outside the Class Mammalia, but it still is surprising to see some animals make use of objects in their environment in inventive ways. Indeed, while the idea that humans are distinguished by the possession of tool use is dead in scientific circles, it still is alive in the public mind (I recently had a friend tell me that we were “Man the Tool-User”), and genuinely impressive utilization of tools by other animals is often related to just be a sort of “trick” or purely instinctual mechanism (I’ll save the issue of animal cognition for another day).

Of the animals that use tools, however, among the most impressive are the Capuchin monkeys (Cebus sp.). Capuchins are platyrrhine primates (New World Monkeys) that inhabit the forests of South and Central America from about Honduras to Brazil. They’re generally familiar to everyone, the proverbial “organ grinder’s monkey,” a common household pet (until recently), and a regular in film roles that required a primate (i.e. Marcel from the show Friends). Indeed, Capuchins are easy to train and highly intelligent, but despite their close proximity to people they’ve generally been overlooked as “just monkeys” for a very long time. Recent research, however, has shown that they can tell us much more about the development of intelligence and human evolution than previously thought.

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Capuchin monkeys cracking open nuts. Note the similarities between this footage and the film shown above.

The fact that chimpanzees have the highest brain-to-body size ratio out of all the African apes is well-known, but few people know that Capuchins exhibit brains of similar proportions. Such a fact is readily apparent (or at least easily researched) but Capuchins have generally been ignored because while they are primates they are not as closely related to humans as Chimpanzees, Bonobos, Gorillas, or Orangutans, but fortunately this has changed. While they can be difficult to study in the wild despite their inquisitiveness/ease of acclimation to human presence, Capuchins are primarily arboreal quadrupeds, able to run through the trees as fast or faster than researchers can make it over the forest floor. This may result in some behaviors being missed, and oftentimes studies are carried out in the dry season when foliage is a bit more sparse and allows for a better view of the monkeys. Why are such considerations important? Because the tool-use in Capuchins I’m about to discuss is more often seen in captivity than in the wild, and it’s important to consider what you may not be seeing when dealing with animals in their natural habitat.

Much of the work on Capuchin intelligence has been carried out in labs by researchers primarily interested in psychology, and as my professor once remarked when considering some of the studies, the background of the researcher can be significant as to what it studied, how it is studied, and how the results are interpreted. Be that as it may, studies in captivity involving Capuchins have shown that they can use tools and that they use tools in a variety of ways depending on the circumstances. Anyone who has used a hammer or other tool to make something recognizes that the way you grip an object has a lot to do with how effective it is going to be; it probably wouldn’t be very effective (or safe) to grip a hammer with the fingertips of both hands and try to use it to bang in a nail. Likewise, when Capuchin monkeys are given a stone and expected to throw the stone into a tub of peanut butter (as in one experiment) they need to choose a grip to accomplish the task, and while there are a number of different variations of grips they usually fall under the category of power grips or precision grips. The names belie what they are used for, and in the throwing experiment I had just mentioned the most popular grip used was called the “jaw chuck,” where an object is held in the palm of the hand with all the fingers holding it in place. The jaw chuck grip was not the most effective in this experiment, however, one monkey having better success during its attempts using a precision grip (the “cup grip,” where an object is held in a cupped hand with the fingers providing support) even though it did not catch on with the other individuals.

In a different experiment, where a tub of peanut butter was covered by an acetate barrier and stones with one sharp edge were placed in the cage, the jaw chuck was even more popular than in the throwing trials, even though similar “power grips” were used as well. Indeed, while the monkeys did use (experiment?) with a number of precision and power grips, the jaw chuck was the most popular overall. Another set of tests, however, showing that monkeys might not use tools at all if they don’t have to. When a tub of peanut butter was covered in 5cm of soil and the monkeys were provided with sticks, the monkeys simply dug with their hands (like baboons do) if the soil was loose. If the soil was hard, however, some of them used sticks, even modifying the sticks by removing leaves and biting off little bits, to reach their prize. This is significant because some people like the !Kung San of the Kalahari use sticks to dig for roots and tubers today and the ability to dig for food underground is considered to be a very important factor in human evolutionary history.

As seen in the video above, however, digging in the dirt isn’t the only thing Capuchins do. They also crack open nuts in a way very reminiscent of Chimpanzees, although not all Chimpanzees exhibit this behavior. Some, like the ones in the Tai Forest do use tools to open nuts (as do other populations), but some populations don’t use tools and some don’t use them in the same way. As I mentioned in my post about Mt. Assirik chimpanzees, the chimpanzees there use the large Baobab tree limbs and trunks as anvils to crack open the fruit of that tree, using a level of tool use lower than that of other populations that put a nut on an anvil and then use a hammer (the Mt. Assirik chimps are just using the tree as an anvil). Again, as described in my earlier post about the Mt. Assirik chimpanzees, tool use can evolve given the proper ecological opportunities and cognitive steps, going from simply using a hammer or anvil on an object to using two tools (hammer and anvil) to open an object to the production of more complex and specialized tools under the proper conditions. In the case of the Capuchins, the monkeys have been known to bang stones together (holding one in each hand), use stones to crack nuts, throw stones against the ground, and hit stones with other stones making a “bipolar” object (it flakes on two sides if held on a stone anvil). Unfortunately I don’t know what becomes of these objects as it seems that Capuchins do not keep or further modify tools they make when they are finished using them, but it could represent the beginnings of tool manufacture, the behaviors requiring the cognitive leap to move ahead.

The cognitive abilities of Capuchins is one of the ways that they differ from Chimpanzees, in fact. While Chimpanzees often recognize themselves if presented a mirror, Capuchins do not (although some have used mirrors to look around objects for hidden food). Capuchins also fail some cognitive tests passed by Chimpanzees, and it seems that while both primates exhibit some similar behaviors the convergence is even more striking because Capuchins are different in terms of their intelligence. Still, the fact that Capuchins can use tools and show convergences with chimpanzees shows us that certain “milestones” that were once considered hallmarks of human evolution can show up multiple times in multiple lineages, recalling the “branching bush” of evolution rather than the orthogenic line.

There are problems with the lab studies, however, and more study needs to be undertaken of wild populations to determine how tools are being used (or even made) in natural groups rather than animals in cages. The behavior of the captive animals will only make sense in terms of evolution when compared to that of wild groups, and it would be a mistake to assume that everything Capuchins do in captivity they must also be doing in the wild. Perhaps they are and we haven’t seen it yet, but perhaps it’s a matter of ecology. If a Capuchin lives in an area with lots of soft fruit and food that does not require tools, they’re not likely to turn to tools to solve some of the problems presented by their environment. If the environment is harsher, however, and the monkeys are not naturally well-equipped to crack open nuts or get the most flesh off bone possible (because Capuchins do eat meat when they can get it), tool use is much more likely to emerge if the cognitive connections can be properly made. Some are more proficient than others, and it make take a while for certain behaviors to become established, but the tool use of Capuchins teaches us some important lessons about evolution and how it is never finished shaping life in the most surprising ways.

References;

Visalberghi, E., and McGrew, W.C. “Cebus meets Pan.” International Journal of Primatology, Vol. 18, No. 5, 1997

Westergaard, G.C. “What Capuchin Monkeys Can Tell Us About the Origins of Hominid Material Culture.” National Institute of Child Health and Human Development,1998.

Westergaard, G.S., and Suomi, S.J. “Capuchin Monkey (Cebus apella) Grips for the Use of Stone Tools.” American Journal of Physical Anthropology, 103: 131-135 (1997)

Westergaard, G.C., and Suomi, S.J. “The Production and Use of Digging Tools by Monkeys: A Nonhuman Primate Model of a Hominid Subsistence Activity.” Journal of Anthropological Research, Vol. 51, No. 1 (Spring, 1995)





I’m going, are you?

4 10 2007

I apologize for the short notice, but I only just found out myself; this Saturday (October 6) NYU is going to host an Evolutionary Anthropology conference in honor of the work of Cliff Jolly. Jolly, basing much of his work on baboons, proposed that seed-eating could have played a significant role in hominid evolution, and the conference will primarily deal with the hypotheses and studies of Jolly. The whole program starts at 9 AM and goes until about 5 PM (with a reception afterwards), and I’ll be headed in with one of my professors Jack Harris, although I don’t know how late I’ll stay as I’ll have to take the train back (if any one has any tips on how to get back to Penn station from NYU, I’d be much obliged). If you’re interested, the program and contact information (RSVP is required) is up online, and if any readers of this blog are going to attend please feel free to drop me a message; I’d be delighted to meet any readers/other bloggers who might be there.





Of feathers, nests, and dinosaurs

24 09 2007

In 2006, researchers Peter Dodson and Steve Wang estimated that perhaps 71% of all the dinosaur genera that ever existed have yet to be discovered, with majority of the genera that we are likely to find potentially being described within the next 100 years. Whether the estimates are correct or not, there can be little doubt that we are in a “Golden Age of Paleontology” (as far as dinosaurs are concerned, at least), the known diversity of dinosaurs increasing at a prodigious rate. While the majority of the as-yet-unknown dinosaurs are still in the ground, we should not forget that the dusty storage rooms of museums and universities can hold startling fossils, too, as paleontological expeditions often collect more than can be carefully studied and described by the scientists. While not a dinosaur, the discovery of the archosaur Effigia okeeffeae from Ghost Ranch, New Mexico in storage at the American Museum of Natural History, has opened many new lines of inquiry for scientists interested in the Triassic. Not all such forgotten fossils need to represent wholly new groups of animals to be significant, however.

It has often been remarked that if the famous specimens of Archaeopteryx from the lagerstatten of Bavaria did not preserve feather impressions, they would have been deigned small theropod dinosaurs (T.H. Huxley was, as far as I am aware, the first to do this, although I do not have the precise quotation at hand). It isn’t surprising, therefore, that this actually occurred several times, the urvogel turning up again in unexpected places. One of the first to come to light was the Teyler specimen, initially discovered in 1855 (five years prior to the discovery of the single feather described in 1861 by Christian Erich Hermann von Meyer). Labeled Pterodactylus crassipes, the fossil would remain “hidden in plain sight” on display in the Teyler Museum in the Netherlands until John Ostrom correctly identified the fossil in 1970. While possibly only a footnote to the larger story, Ostrom’s discovery created a taxonomy problem as well; because the Teyler specimen was older, traditionally the species name crassipes would have priority over lithographica (Pterodactylus obviously not applying because Archaeopteryx was not a pterodactyl). The name Archaeopteryx lithographica had been used prominently in the literature for over 100 years, however, and so (thankfully) the species name of the early bird remained lithographica.

Eichstatt specimen
A replica of the Eichstatt specimen of Archaeopteryx, on display at the AMNH.

After Ostrom’s find, other specimens started to appear, often confused with the dinosaur Compsognathus, also known from the Solnhofen limestone of Germany. In 1973 F.X. Mayr discovered what is now known as the Eichstatt specimen, which he sent to Peter Wellenhofer in order to confirm its true identity. Later, in 1988, Wellenhofer himself discovered another specimen that had been labeled Compsognathus in the collection of the former mayor of Solnhofen, and Wellenhofer again ran into Archaeopteryx in 1992 when a smaller specimen came out of the Solnhofen limestone.

Archaeopteryx
Gerhard Heilmann’s exquisite illustration of the Berlin Archaeopteryx from his work The Origin of Birds.

Such confusion between Compsognathus and Archaeopteryx show the importance of careful examination and taphonomy to paleontology, however; the chief reason why several specimens were misidentified was due to their lack of feather impressions. The exquisite preservation that makes the Berlin specimen of Archaeopteryx a work of natural art is even rarer than the collected remains of the genus itself, and a simple matter of burial environment can seemingly make all the difference. Indeed, in an age where feathered dinosaurs continue to astonish scientists and the public alike, the presence of absence of feathers on larger animals can be problematic. While smaller dinosaurs like Sinosauropteryx and early birds like Confusciusornis are often found preserved in ash falls that allow their discoverers to make out their feather coverings, larger animals may not be covered up as quickly or have such fine detail preserved, as seen from the partial skeleton of Gigantoraptor described in Nature earlier this year. While it is not unreasonable to infer that the giant Oviraptor-like dinosaur had feathers covering its body for at least some of it’s life based upon its relationships to known feathered dinosaurs, no hard evidence of feathers was found, so what sort of feathers it had, how much of its body was covered, and other details remain (for the time being) largely unanswerable. In fact, feather impressions associated with Gigantoraptor may never be found, but some new research involving it’s cousin Velociraptor may provide some clues as to whether the large oviraptorid had plumage or not.

The medium-sized theropod Velociraptor was discovered during the famous American Museum of Natural History expeditions led by Roy Chapman Andrews to the “Flaming Cliffs” of Mongolia during the early 1920’s, and the first remains of Velociraptor to be examined gave the researchers the impression that it was capable of catching relatively large, quick prey with its hands. While certainly an impressive dinosaur, Velociraptor was not as popular as it’s dromeosaur relative Deinonychus, although Gregory S. Paul’s popular book Predatory Dinosaurs of the World started the ball rolling to get Velociraptor to be a household name. While Paul’s book was insightful and prescient in many ways (including its depictions of feathered dinosaurs), the taxonomy in the work was a bit strange, lumping Deinonychus under the genus Velociraptor. This wouldn’t have been of much ultimate consequence, except the book was timed just right to have an important influence on Michael Crichton while we wrote the best-selling novel Jurassic Park, the name Velociraptor being attributed to Deinonychus. This tradition was carried on in the blockbuster film adaptation and in two sequels, the name Velociraptor overshadowing Deinonychus in prestige. As mentioned previously, however, despite the taxonomic reshuffling Paul’s book was important as it drove home the evolutionary relationship between dinosaurs and birds, and in recent years many dinosaurs have come out of Asia showing that they were covered in feathers.


The skull of Velociraptor. From Osborn, H.F., et al. “Three new Theropoda, Protoceratops zone, central Mongolia.” American Museum novitates ; no. 144. 1924

So, how can we tell if dinosaurs that were not find with associated feather impressions had feathers or not? Until now, feathers are often implied for dromeosaurs during at least some stage of life due to evolutionary relationships, but a new (albeit short) paper by Alan Turner, Peter Makovicky, and Mark Norell shows that there are osteological features that tell of the presence of feathers. Along the ulna of a Velociraptor specimen from Mongolia, 14 bumps about 4mm apart were found in a straight line along the bone, directly corresponding to the same structures in living birds, the bumps serving as an anchor for the secondary feathers. This is an amazing find, especially since Velociraptor shows the presence of actual feathers, not just the “fuzz” or integumentary fibers seen on related dinosaurs like Sinosauropteryx. I have to admit that I chuckled a little when I saw one reproduction of Velociraptor covered in feathers, arms obscured by secondaries, but now it seems that such a reconstruction is much closer to the truth than the traditional leathery-skinned model. While the authors of the paper do note that some dinosaurs could have had feathers while the secondary feather anchors were absent, the presence of such a trait gives us a new feature of the bone that can be used to determine whether a dinosaur had feathers or not, and I hope a larger re-investigation of the ulnas of dromeosaurs will be undertaken as it could help determine the presence of feathers on species too big to have them properly preserved.

Quill Comparison
The anchors for the secondary feathers in Velociraptor and a Turkey Vulture. From Turner AH, Makovicky PJ, Norell MA (2007) “Feather Quill Knobs in the Dinosaur Velociraptor.” Science 317(5845):1721.

Still, the question of what was Velociraptor doing with secondary feathers remains. It had previously seemed plausible that many of the non-avian dromeosaurs could have lost some of their feathery coverings, possibly only being covered with feathers as a juvenile. This fossil refutes such a notion for Velociraptor, at least, and secondary feathers could have had any number of uses. While they likely didn’t help much in terms of an individual dinosaur’s thermoregulation, they could have been used for signaling/communication, sexual selection, or been used in the temperature regulation of nests. Personally, I think all these factors could have played a role to a greater or lesser extent, but it is the nest hypothesis that interests me the most.

Troodon nest
A non-feathered reconstruction of Troodon on a nest. From Horner, J.R. “Dinosaur Reproduction and Parenting.Annu. Rev. Earth Planet. Sci. 2000. 28:19–45

Those who know their paleo-history will recall that Velociraptor was not the only new theropod to be discovered by Roy Chapman Andrews and his crew. Oviraptor was also uncovered during the expeditions, and the presence of the dinosaur in association with some of the first-known dinosaur eggs gave paleontologists the impression that the theropod was stealing the eggs (hence the name Oviraptor).

Oviraptor nest
An oviraptorid theropod in a brooding position over a nest. From Clark, J.M., Norell, M.A., and Chiappe, L.M. “An oviraptorid skeleton from the late Cretaceous of Ukhaa Tolgod, Mongolia, preserved in an avianlike brooding position over an oviraptorid nest.” 1999. American Museum novitates ; no. 3265

Such an interpretation was not to last, however. Research by AMNH staff during the 1990’s showed that the “Protoceratops” eggs that H.F. Osborn and other scientists thought Oviraptor was stealing were really Oviraptor eggs to begin with, the embryo of one of the tiny theropods being preserved inside and allowing for identification of certain eggs with a particular variety of dinosaur. This relationship was further strengthened by the analysis of an oviraptorid dinosaur, probably Oviraptor, in a brooding position on top of a nest. The preservation of this specimen indicates that it died on top of the nest and was not deposited on it after being moved from elsewhere, there being little disturbance to the nest and parent overall. While the discovery of such behavior is momentous in and of itself, if we apply the discovery of secondary feathers in Velociraptor to the oviraptorid (a close evolutionary relative) it would seem that the dinosaur was shielding the eggs with the hypothetical feathers. This is still conjectural, and the oviraptorid would have to be closely investigated to determine whether it had secondary feathers or not, but I don’t think it’s out of the question to infer that, should this oviraptorid be found to have secondary feathers, it was fanning them out over its eggs when it died.

Oviraptor Nest
An oviraptorid sitting on a nest, reconstructed as Citipati. From Clark, J.M., Norell, M.A., and Chiappe, L.M. “An oviraptorid skeleton from the late Cretaceous of Ukhaa Tolgod, Mongolia, preserved in an avianlike brooding position over an oviraptorid nest.” 1999. American Museum novitates ; no. 3265

Given such bird-like behavior in the oviraptorids, it may come as a surprise to find that non-avian theropod dinosaurs may not have had a reproductive cycle like that of modern birds. In a paper released earlier this year, Gregory M. Erickson and others determined that four oviraptorids and one Troodon-like theropod studied seemed to show a more reptilian mode of growth, in that sexual maturity was reached as growth slowed down. This differs from the reproductive modus operandi of living birds, which grow to full size long before breeding begins. While it seems that the dinosaurs, like living crocodiles, took more than a year to reach adult size but attained sexual maturity as adult size was achieved, living birds show explosive growth rates that allow them to reach adult size in much less than a year, yet they are not sexually mature for some time afterwards. Indeed, in dinosaurs it seems sexual maturity was size-linked, while in birds this relationship was decoupled.

Oviraptor Nest
On oviraptorid, Citipati, on top of a nest. From Erickson, G.M. et al. “Growth patterns in brooding dinosaurs reveals the timing of sexual maturity in non-avian dinosaurs and genesis of the avian condition.Biology Letters Volume 3, Number 5. October 22, 2007

Despite the difference in growth patterns and life cycles, it is starkly apparent that birds evolved from theropod dinosaurs, some of their closest relatives being the dromeosaurids like Velociraptor. The “big idea” of a evolutionary relationship between dinosaurs and birds has been firmly established, but there are many questions that have yet to be resolved. Helping to further clarify the picture of bird evolution, another recent paper by Alan Turner, et al. (also appearing in Science) describes the new dinosaur Mahakala
omnogovae
, which shares a number of features with birds but not later dromeosaurs.


Dromeosaur Phylogeny

Phylogenetic tree of Paraves, taking temporal factors into account and reflecting changes in body size (click for larger image). From Turner, A.H. et al. “A Basal Dromaeosaurid and Size Evolution Preceding Avian FlightScience 317, 1378 (2007)

What is surprising about Mahakala is its mix of features and it’s small size. For some time one of the big questions of bird evolution has been “Why did relatively large dinosaurs shrink to take wing?” I had always felt that this was putting the cart before the horse a bit, but now Mahakala has offered up fossil evidence that the large size seen in later dromeosaur celebrities like Velociraptor is a derived condition, the common ancestor probably being no larger than Archaeopteryx.

What does trouble me about this find is it’s age; Mahakala is Campanian (83.5-70 mya) in age. As made clear by the temporal arrangement of the phylogenetic tree, this makes Mahakala much older than Archaeopteryx, Confuciusornis, Yixanornis, and other birds. While Mahakala can tell us much about evolutionary history and has shown that troodontids and dromeosaurids shared a common ancestor which in turn shared a common ancestor with birds (helping to explain those nice secondary feather characteristics in Velociraptor), I am more anxious to see if older, Jurassic relatives can be found. The dinosaurs coming out of Mongolia and China are fantastic finds, but I still find the time disparity between Archaeopteryx and its Cretaceous cousins to be irksome. I’m not the first to bring up such issues either, and I have to say that I do agree with the perspective of Peter Dodson; we need to look at the “big picture” if we’re going to figure this out. In a paper entitled “Origin of Birds: The Final Solution?” Dodson writes;

A philosophy of critical realism seems more congenial for analysis of evolutionary biological individuals having a real history [than cladistics alone]. Cladistics uses parsimony as a first principle, which may be rejected on the grounds that nature is prodigal in every regard. Parsimony based on morphology suffices only when there are no other data sets to consider. Cladistics systematically excludes data from stratigraphy, embryology, ecology, and biogeography that could otherwise be employed to bring maximum evolutionary coherence to biological data. Darwin would have convinced no one if he had been so restrictive in his theory of evolution. The current cladistic analysis of bird origins posits a series of outgroups to birds that postdate the earliest bird by up to 80 million years. This diverts attention from the search for real bird ancestors. A more coherent analysis would concentrate the search for real avian ancestors in the Late Jurassic.

As Dodson notes, morphological analysis alone is not going to get the job done, although I was much relieved by the fact that Turner, et al. used a time scale in constructing their tree. Especially concerning birds, I had always wondered why I would occasionally see animations of Deinonychus growing feathers and flying away as a Canada Goose when Arcaheopteryx was much older. It should be noted that Archaeopteryx is the oldest known bird, not necessarily ancestral to all later birds, but I would hope that more focus would be given to the Jurassic in the search for bird origins as I think the most important fossils to the origins of birds are far older than Mahakala. The chief problem with uncovering the most distant past, however, is that factors of taphonomy might inhibit identification of early bird relatives, especially if they are not preserved in lagerstatten deposits. The fine preservation of so many feathered dinosaurs are partially what has made them so popular, and unless fossil beds resulting from ash falls or ancient lagoons are found, the search for the “early birds” may prove to be exceedingly difficult.

The fossil finds recently reported in Science and elsewhere are definitely important, especially since they shed new light on the evolution of birds and of their dinosaurian relatives. Some, however, have greeted the recent studies with groans; hasn’t everyone had enough of feathered dinosaurs? Such attitudes are unfortunate, as there is still much to learn from specimens that have already been known for a long time. Constant revision and careful reanalysis are the bread-and-butter of good science, and I don’t think any generation of workers should be content with saying “It’s been done” and assume that everything they’ve been told previously is still true. This is not a call to develop new hare-brained hypotheses for their own sake, but rather a plea to keep going back to the dusty shelves of museum basements, to take another look at structures that were initially described decades ago, and to try and keep the bigger evolutionary picture in mind in the search for new specimens. There is too much to learn for any one person to take on these tasks on their own, but as a community I think scientists can still make old bones give up new secrets.

References;

Clark, J.M., Norell, M.A., and Chiappe, L.M. “An oviraptorid skeleton from the late Cretaceous of Ukhaa Tolgod, Mongolia, preserved in an avianlike brooding position over an oviraptorid nest.” 1999. American Museum novitates ; no. 3265

Dodson, P. “Origin of Birds: The Final Solution?American Zoologist. Volume 40, Issue 4 (August 2000)

Erickson, G.M. et al. “Growth patterns in brooding dinosaurs reveals the timing of sexual maturity in non-avian dinosaurs and genesis of the avian condition.Biology Letters Volume 3, Number 5. October 22, 2007

Horner, J.R. “Dinosaur Reproduction and Parenting.Annu. Rev. Earth Planet. Sci. 2000. 28:19–45

Nesbitt, S. “The Anatomy of Effigia okeeffeae (Archosauria, Suchia), Theropod-Like Convergence, and the Distribution of Related Taxa.Bulletin of the American Museum of Natural History. Number 302, Issue 1 (January 2007)

Osborn, H.F., et al. “Three new Theropoda, Protoceratops zone, central Mongolia.” American Museum novitates ; no. 144. 1924

Paul, G.S. Predatory Dinosaurs of the World. Simon & Schuster, NY. 1988

Shipman, Pat. Taking Wing. Touchstone, NY. 1998

Turner AH, Makovicky PJ, Norell MA (2007) “Feather Quill Knobs in the Dinosaur Velociraptor.” Science 317(5845):1721.

Turner, A.H. et al. “A Basal Dromaeosaurid and Size Evolution Preceding Avian FlightScience 317, 1378 (2007)

Wang, S.C., and Dodson, P. “Estimating the diversity of dinosaurs” PNAS. September 12, 2006, vol. 103 no. 37 13601-13605





When your dials are pupilated…

21 09 2007

Drop what you’re doing; Neil has one of the most singularly excellent posts I have ever seen up over at microecos about the eyes of the Aye-Aye, a very rare and bizarre endangered strepsirhine primate that is truly unusual (and, although the “rodent-like” characters of the Aye-Aye are likely derived characters, famous morphologist W.E. le Gros Clark suggested in The Antecedents of Man, truly shows that primates evolved from animals like shrews). [Many thanks to those in the comments that corrected my bad phrasing] There is such a thing as being too bizarre, however, and even though habitat loss is a huge problem for these animals, so is the local mythology; the aye-aye is so weird that local legends deem them to be evil creatures, and they are often killed to prevent them as they are seem as symbols of death and evil. Now that’s enough of my yammering; check out Neil’s essay, post haste!





Amalgamated Anthro News

19 09 2007

Much to my astonishment, I’ve actually started to receive some news items that people would like me to talk about here on Laelaps, and the past 24 hours or so has been full of anthropology-oriented news.

First up is a talk given by Zeresenay Alemseged, the discoverer of “Selam,” the Australopithecus afarensis child detailed about a year ago in the journal Nature. Brought to us by the Technology, Entertainment, and Design Conference, the talk can be found in either mp4 or zip form (it’s a video) here. The dreaded “March of Progress” rears it’s ugly head, but otherwise it’s an interesting summary if you’re not familiar with the discovery.

I also received notification of a new article in Scientific American (just about the only popular science magazine I don’t presently subscribe to, I think) about “The Trouble With Men.” At first, seeing only the title, I thought I was in for another evolutionary psychology (or “sociobiology”) rant about how inherently evil males of the species Homo sapiens are, but the reality of the article is far more interesting. According to the article, Virpi Lummaa of the University of Sheffield has found that there is something of a higher price to be paid for male offspring in our own species than for daughters, the course of development being more costly on the mother and siblings (both in and out of the womb) than previously suspected. While the data to back up the observations Lummaa has made are still wanting, studies on development in other animals suggest that testosterone has a lot to do with the problems experienced by females, especially if a mother gives birth to opposite-sex twins (the female might even be born sterile as a result of the testosterone influence).

How significant Lummaa’s studies are to modern society is also in question, as she primarily derived her observations from church records from over two centuries ago about premodern mothers among the Sami people of Finland. While such a time period may be slight, the cultural and technological changes have been great, which complicate the application of the data to people living today;

Access to effective birth control, an abundance of food, and low child mortality rates would all obscure the evolutionary influences seen in the preindustrial data. “It’s almost a shock when you realize that 100 to 150 years ago, 40 percent of babies died before they reached adulthood,” even when adulthood was defined as age 15, Lummaa notes.

Still, many, if not most, of the people in the world do not live in an industrialized society, so there is still plenty of opportunity to see if the observed trend still holds. For some reason Scientific American makes no mention (and provides no link) to the study that inspired the article, appearing in the June 26 edition of PNAS and by Lummaa, et al., entitled “Male twins reduce fitness of female co-twins in humans.” From what I can glean from the abstract, the authors argue from an entirely hormonal origin for reduced reproductive success in female twins born with a male brother, even if the brother dies at some point. Societal and cultural values do not seem to make a difference in the group studied, although I am still a bit dubious about the assertion that culture doesn’t compensate and would like to see a similar study undertaken with extant groups of people so more detail can be taken in. Regardless of how accurate the conclusions may or may not be, it is interesting to me personally as I am friends with a family where the mother had two sets of twins, each pair consisting of a boy and a girl.

Still, the idea that males might be favored in one way or another is not so strange an idea, especially since it’s becoming apparent that evolution can work on males in females of the same species in different ways. A study revealed earlier this year about Red Deer seem to show that what makes a successful male deer does not make a successful female deer (and vice versa), and another study involving White Rhinoceros showed that male offspring are favored when it comes to receiving milk from their mothers. The more we learn about species, the more dynamic and interesting things become, and before the study on deer I can’t say that I had considered the idea that an especially successful male deer might produce sub-par female offspring as a result of his prowess (although any sons would gain the benefit of dad’s genes).

Finally, the new issue of Natural History has an article about the skeleton of “Lucy” going on tour in the U.S. by AMNH paleoanthropologist Ian Tattersall. He writes;

Dinosaur bones and many other fossils routinely hit the road, but fossils of extinct hominids tend to be treated as sarcosanct, never allowed to leave their home institutions, let alone their countries of origin. That is regrettable, in part because such fossils are the patrimony of all humankind. Furthermore, paleontology is quintessentially a comparative business: no fossil can be satisfactorily understood in isolation from the wider record.

I’m still not entirely sure how I feel about the bones of Lucy going on tour; I would prefer them to stay safe because they do belong to all mankind (and not just my generation or paying customers at various institutions), but I won’t lie and say I will stay home when her remains come to New York. Also, I have heard from many a paleontologist that they wish America was a bit more strict about its fossils and where they can be taken after being discovered. Many countries, while allowing fossils to be taken to various institutions for study for a number of years, want the remains of organisms from their own country returned for storage, study, or display after a certain amount of time, and as far as I am aware the U.S. has not followed suit.

Many thanks to those who notified me of the new articles and videos; I will continue to write about whatever news is sent my way as often as I can, so if you see something that catches your eye and think should get some attention, send it on in. And, before I forget to mention it again, be sure to check out the new look of The Panda’s Thumb.





A peek at my homework

19 09 2007

Here’s the summary that I’ll be giving today in my Topics of African Prehistory course pertaining to the assigned reading Wrangham, R. 1987. “The Significance of African Apes for Reconstructing Human Social Evolution.” In Warren G. Kinzey (Ed.) The evolution of Human Behavior: Primate Models. It’s long by summary standards, but when have I been known to be succinct? In fact, I would have loved to make this even longer, but I don’t want to talk my classmates to death.

Summary

“Life is a copiously branching bush, continually pruned by the grim reaper of extinction, not a ladder of predictable progress. Most people may know this as a phrase to be uttered, but not as a concept brought into the deep interior of understanding. Hence we continually make errors inspired by unconscious allegiance to the ladder of progress, even when we explicitly deny such a superannuated view of life.” – Stephen Jay Gould, Wonderful Life, 1989

On June 30, 1860, “Darwin’s Bulldog” T.H. Huxley met Bishop “Soapy Sam” Wilberfoce in a debate on one of the most hotly contested topics ever to be put before mankind: are we evolved, or are we divine creations? While no one is quite certain as to the outcome of the debate, it is perhaps one of the most celebrated events in the history of the evolution idea, for when the Bishop rhetorically asked whether it was through his grandmother or grandfather that he was descended from a monkey, Huxley delivered this devastating rejoinder; “If then the question is put to me would I rather have a miserable ape for a grandfather or a man highly endowed by nature and possessing great means and influence and yet who employs those faculties and that influence for the mere purpose of introducing ridicule into a grave scientific discussion – I unhesitatingly affirm my preference for the ape.” Such wit did not halt the debate then and there, but as Huxley’s work Man’s Place in Nature, Darwin’s The Descent of Man, and various cartoons from Punch at the time make clear, it could no longer be denied that Homo sapiens had very close relations to the living gibbons, orangutans, gorillas, and chimpanzees, their lives providing insight into our own.

The relationship between men and apes is now taken as a “given” (and rightly so), but the question of just what living apes can tell us about our past must be asked. While the fossil record seemingly refused to give up hominid remains for some time, there is today a greater diversity of fossil hominids now known than in Huxley’s time, and what we know about living apes must be reconciled with these discoveries if we’re to accurately portray what our ancestors (even our common ancestors) may have been like. Indeed, we should not forget that our own species did not evolve from chimpanzees or gorillas but rather shared common ancestry with them in the past, and they have been evolving since the time of their separation just as we have. As Richard Wrangham rightly criticizes the approach of trying to crown a living species as the archetype for our ancestor, noting “The ideas these models generate are plausible and even thought provoking, but their value is limited by their initial assumption: they assume that the social organization of human ancestors was similar to that of living species.”

Given this potential pitfall, Wrangham suggests a behavioral sort of cladistics, surveying the social behavior of extant gorillas, chimpanzees, and bonobos in order to find the presence (or absence) of shared social behaviors. If certain behaviors exist within all the groups mentioned, then there would be reason to believe (at least in terms of parsimony) that such behaviors were inherited from a common ancestor rather than evolved multiple times. Concerning the closed or semi-closed social groups detailed in II A 2. (Grouping Patterns) of the outline, it appears that humans, chimpanzees, and gorillas all have closed or semi-closed social groups, making the behavior a shared trait that may have been shared by the common ancestor of all the groups. On the other hand, however, we have the data presented in II B 4. (Male-Male Interactions) where the variety of interactions precludes us from being able to tell what sort of behavior pattern our common ancestor exhibited in terms of male interactions.

Now that we understand the application of Wrangham’s methodology to living primates, we should consider the overall strengths and weaknesses it may have. One of its strengths may be the ability to recognize the possession of common behavior in the apes despite different ecologies. If humans, chimpanzees, bonobos, and gorillas all share certain behavioral characteristics despite living in different habitats or inhabiting different niches, the overall case is stronger for that trait being inherited from a common ancestor rather than convergent evolution. Convergent evolution can be problematic, however, as it sometimes seems to defy parsimonious explanations. Perhaps the common ancestor did not exhibit the behaviors now expressed as much carry a capacity for them through variations in populations (being that it is populations that speciate and change, not an entire species as a whole), and being that we are dealing with behavior and not morphology in this case, it might be easy to accentuate some similarities/differences while hiding others. For example, if we undertake cladistics in the traditional sense, let’s say describing a skull, the process is relatively straightforward; either a structure or trait is present or it is not. Behavior, however, can be more variable, and even in Wrangham’s description of Group Patterns there can be seen some potential for disagreement. Indeed, is there are large significance between a closed group and a semi-closed group? Again, given that we’re talking about behavior and not a morphological trait that is usually clearly present or absent, researchers would do well to be mindful of how they delineate what they consider significant behaviors and how they are measured in terms of this method.

Wrangham does not hold his method up as the one and only answer, however, and he concedes that it is more of a “quick” and “weak” starting point to determine possible similarities rather than a way to obtain ultimate answers. In fact, as he notes in the introductory paragraphs, the study of behavioral ecology weighs heavily on the issues herein discussed, although it is a discipline still in development. Even beyond modern ecology, paleoecology will have a very significant role to play in determining what our ancestors were like, especially because habitat does much to shape the bodies and behaviors of organisms through evolution. Indeed, living species can give us valuable insights into our past, but if the information gleaned is determined to be the product of convergence or is found not to be consonant with the data from the fossil record, developing understanding will have to accommodate such discoveries. Ultimately, the discovery and determination of our common ancestors with chimpanzees and gorillas will weigh heavily on this issue, but at the present time the information is overall insufficient and (as ever) there are more questions than answers. For the present, however, the behavior of living African apes can provide a sufficient framework for comparison, and Wrangham’s methodology provides a quick way to spot potential similarities that can then be checked through the study of ecology and the fossil record.





Beating fossil horses: Creationists take on an “Icon of Evolution”

17 09 2007

Horse Evolution MacFadden 2005
A representation of our modern understanding of horse evolution, having some beginning diversity, a sort of “Oligocene Bottleneck,” and then a wide profusion of diversity throughout the New and Old World. From McFadden, Bruce. 2005. “Fossil Horses – Evidence of Evolution.” Science Vol. 307. no. 5716, pp. 1728 – 1730

As discussed previously in my summary of horse evolution, the development and radiation of various equids over the past 55 million years is one of the most celebrated examples of evolution in action. While we are fortunate to have such detailed examples of past evolutionary transitions, the presentation of the evolution of horses proceeding in a straight line from small, four-toed Eohippus to the extant Equus has sometimes done more harm than good. While the branching bush of horse evolution has been recognized in scientific circles since the middle of the 20th century (at the latest), a more orthogenic model has often still been presented in popular works and taught in schools, and David Godfrey has corroborated this in the comment thread of my previous essay. It is this weakness in using a “simple” illustration that has opened the door up to creationist complaints, and in this appendix to my original work I will attempt to review some of the more recent remarks made by the likes of Jonathan Wells (affiliated with the Discovery Institute) and Ken Ham (president of Answers in Genesis) on the evolution of horses.

Simple horse diagram
Comparison of Eohippus to Equus. There’s a lot of evolution in that dashed line. From “The Dawn Horse or Eohippus” by Chester Stock (1947).

The book that introduced me (albeit painfully) to intelligent design and critics of evolution was the infamous Icons of Evolution by Jonathan Wells, and in it Wells spends an entire chapter attempting to discredit the idea that horses evolved. This is not surprising, especially given that horse evolution was so triumphantly heralded by none other than “Darwin’s Bulldog” Thomas Henry Huxley in 1876. Indeed, the rich amount of fossils uncovered, plus public interest and prestige allowed horses to take on an iconic status, caused the transitions among fossil horses to become one of the most widely-cited examples of evolution, the change from small, multi-toed ancestors to large, one-toed descendants making for a very compelling scientific narrative.

Despite the vast amount of fossil evidence available that proves, beyond doubt, the evolution of horses, Wells spends little time addressing the very topic that gives the chapter “Fossil Horses and Directed Evolution” it’s name. Wells quickly covers most of the history that I have myself summarized (and, at the risk of sounding conceited, I believe more aptly summarized), but he quickly turns to an attack on G.G. Simpson, Charles Darwin, and Richard Dawkins on tenuous philosophical ground rather than bring any closure to his chosen subject. In fact, it seems like the selection of horse evolution as one of his “Icons” was merely a set-up, and while it is not explicitly stated, the purpose of the chapter is to dust off the old idea of orthogenesis. Working primarily from the work of Matthew and Stirton (see the previous essay) from the first half of the 20th century, Wells states the following about the illustrations of horse evolution that appeared in the AMNH papers;

Despite having been revised, the picture of horse evolution still includes a line connecting Hyracotherium with its supposed descendants, all the way up to the modern horse. Ironically, this very Darwinian line of ancestor-descendant relationships still presents a problem for neo-Darwinists like Simpson, because it is as consistent with directed evolution as the linear series in the old icon. The mere existence of extinct side-branches doesn’t rule out the possibility that the evolution of modern horses was directed. A cattle drive has a planned destination, even though some steers might stray from a herd along the way. Or, to use another analogy, the branching pattern of arteries and veins in the human body has some randomness to it, but our very lives depend on the fact that the overall pattern is predetermined.

This doesn’t prove that directed evolution is true, but only that a branching-tree pattern in the fossil record doesn’t refute it. A straight line and a branching tree are equally consistent (or inconsistent) with the existence (or non-existence) of either a predetermined goal or an inherent directive mechanism. In other words, even if we knew for sure what the pattern was, that alone would not be sufficient to establish whether or not horse evolution was directed.

Stirton Horse Phylogeny
From Stirton, R. A. 1940. “Phylogeny of North American Equidae”. Bull. Dept. Geol. Sci., Univ. California 25(4): 165-198.

So there you have it, folks. Horse evolution appears to have a branching pattern because some lineages didn’t follow God’s plan during his 55-million-year-old evolutionary cattle drive. Wait, what? Either intentionally or as a result of lack of thought on the subject, Wells speaks out of both sides of his mouth in this passage, attempting to be a sort of Devil’s Advocate. In classic intelligent-design style, the identity of the force that Wells contends could have given direction to horse evolution is never mentioned, and it is only stated that such considerations cannot be ruled out. This sounds tentative, but the rest of the chapter is an attack on the concept that evolution does not have any sort of direction to it, diversity being a result of entirely natural processes (and not a divergence from some ill-defined bauplan ordained by a supernatural force). This sort of doubletalk is maddening and will appeal to those already inclined to agree with Wells, the gaping holes in his argument being obvious to anyone who is more familiar with the topic that the DI writer.

Wells also attempts to confuse the reader as to how evolution proceedings by taking certain ideas to extremes. By Wells’ logic, a branching pattern means that every genus must have a diversity of descendants, and if there seems to be any sort of anagenesis then that shows that evolution had direction. This view is certainly mistaken, but Wells seems to use it primarily as a rhetorical device to spark incredulity in the reader, and it might be all-too-easy for those unfamiliar with evolution to be taken in. The truth of the matter is that we can create a lineage of representative types showing the transition of horses from Eohippus to Equus to the exclusion of other genera, but such is a narrow view. This sort of representation, which persisted much longer than it should have in general or popular accounts, has done much to confuse the issue, even though the very people who have put forth the “simplified” model have recognized there was a greater diversity. It seems to be something of a fight between showing evolution as we know it to be and between trying to convince the reader that evolution has occurred, usually showing a phylogeny that is close to that of O.C. Marsh.

OC marsh Phylogeny
O.C. Marsh’s concept of “The Geneology of the Horse,” a decidedly straight-line progression. From Marsh, O.C. 1879. “Polydactyly Horses, Recent and Extinct.”

The bait-and-switch tactic of Wells in his book, as we have seen, is not very straightforward or even conclusive, but young earth creationists (YEC’s) tackle the problem in a different way, attributing the existence of horses to a definite intelligent agent: God. While generally silent about horses in their popular tracts The Lie and Refuting Evolution, the #1 creationist group in the United States (for the moment, anyway, as creationist ministries seem to have a bang-and-bust cycle) Answers in Genesis has a few articles on the subject available on their website. In an 1999 article, Jonathan Sarfati (now with Creation Ministries International,due to a schism within AiG) wrote “The non-evolution of the horse: Special creation or evolved rock badger?” in which he pontificates on why there are so many fossil horses with extra toes, low-crowned teeth, and of smaller stature;

An important part of the biblical creation model is that different kinds of creatures were created with lots of genetic information. Natural selection can sort out this pre-existing genetic information, by eliminating creatures not suited to a particular environment. Thus many different varieties can be produced in different environments. Note that this sorting process involves a loss of information, so is irrelevant to particles-to-people evolution, which requires non-intelligent processes to add new information.

Also, much of this (created) genetic information may have been latent (hidden, i.e. the features coded for are not expressed in the offspring) in the original created kinds. They also had other controlling or regulatory genes that switch other genes ‘on’ or ‘off.’ That is, they control whether or not the information in a gene will be decoded, so the trait will be expressed in the creature. This would enable very rapid and ‘jumpy’ changes, which are still changes involving already created information, not generation of new information.

Applying these principles to the horse, the genetic information coding for extra toes is present, but is switched off in most modern horses. Sometimes a horse is born today where the genes are switched on, and certainly many fossil horses also had the genes switched on. This would explain why there are no transitional forms showing gradually smaller toe size. [emphasis mine]

As can be easily seen, Sarfati attempts to escape into the realm of genetics, throwing around lots of scientific-sounding arguments in a feeble attempt to dazzle readers. One of the central philosophical doctrines of modern creationists is the necessity of the Fall (or the entrance of death and disease into the world as a result of Adam & Eve’s sin in Eden), and much of what creation ministries write circles around the degeneration or “devolution” of all life since the eviction from Eden. This is not the entire story, however, as the Noachian Deluge is of nearly equal importance, all animals alive today being (in the YEC view) descendants of survivors of the great flood. In order to make the vast diversity of fossil horse species consonant with such views, Sarfati even has to invoke a kind of punctuated equilibria (although I’m sure he’d never admit it), three-toed horses evolving at an exceptional rate within the last few thousand years, only to instantaneously go extinct. Sarfati could have said that horses like Pliohippus were alive before the Flood (their fossils being explained by the catastrophe), and while still horribly wrong it would at least make a little more sense. Sarfati decides to stick with saltational changes in horses in a post-flood world, however, pointing to the products of artificial selection in horses (especially in terms of size) as if they had occurred on their own in nature.

As is often the case with creationists, Sarfati’s thesis seems based on what was cutting-edge science during the end of the 19th century, and there is nary a mention of newer research by scientists like Bruce MacFadden (or even many of the paleontologists who worked on horses during the mid-20th century like Stirton and Matthew). Indeed, it seems as if he merely picked up some other creationist tracts, dumped them into a blender with some snippets from a basic genetics book, mixed it up, and wrote down whatever came out of the amalgamated bits and pieces. Sarfati must be given some credit in putting forth an idea as to the origins of the vast diversity of fossil horses (see the illustration at the beginning of this appendix); most other creationists have been content to signal the “death knell” of horse evolution and merely state it as an abandoned hypothesis that evolutionary scientists no longer want to discuss. In the book The Amazing Story of Creation From Science and the Bible, YEC-fave Duane Gish writes;

Even evolutionists acknowledge, however, that we cannot find transitional forms between these various kinds of horses. There are no fossil horses with part-browsing, part-grazing teeth. We cannot find fossils of a horse with three-and-a-half toes or two-and-a-half toes. The fossils show no progressive increase in size. In fact, some “later” horses were smaller than “earlier” horses. The number of ribs did not progressively increase. The number of ribs in fossil horses go up and down. Just as there are different kinds of primates today – lemurs, monkeys, apes, and humans – so there were different kinds of horses in the past, with no evidence that one kind of horse evolved from another kind of horse. Just as dinosaurs and many other kinds of creatures have died out since creation, so, also, many different kinds of horses died out. Evolutionists still search, and will continue to do so, without success, for the transitional forms which much exist, if evolution is true.

What is truly odd about Gish’s statement is that he expects modern scientists to believe in an orthogenic progression (similar to the rhetorical attempts of Wells, as mentioned above), anything that runs counter to that decimating Gish’s straw man. Just like Wells, he also attempts to spark some amount of incredulity in the reader, suggesting that toes disappear piecemeal, bone by bone, rather than overall reductions and changes that have left vestiges in Equus today. Gish’s comment about teeth is also strange, as if he expected horses to think “Hmmm, I want to be a grazer, not a browser; better start changing my teeth!” It is the changes in ecology in which a population exists in and the branching out into new niches that puts pressure on existing characters to shape the organisms, and there is no cosmic force that decides that in 10 million years time the teeth of the animal should look a certain way and push it towards that goal. In fact, Gish’s creationist views are far closer to the straw man that he mocks than the scientific truth of the matter, but it seems that such a philosophical relationship is often lost on YEC’s.

Even stranger and false than Gish & Sarfati’s works, however, is Lawrence Richards’ It Couldn’t Just Happen. Rather than suggesting that scientists are merely misguided or that they have abandoned horses as an example of evolution, Richards attributes to them some amount of dishonesty (or at least fanciful thinking);

But why did evolutionists ever think fossils from different parts of the world should be linked together in the first place? Part of the reason is that they were tricked by their own theory. The Theory of Evolution said that modern animals should develop from similar but different animals of the past. It said that hooves should be an adaptation and have developed from several toes to one. Size would help a horse survive by enabling it to run faster, so animals should gradually become larger. Simply put, evolutionists fit the fossil bones of different animals into a series and said they were horses, because the bones fit their Theory of Evolution!

It’s almost as if you were outside one day and found a tennis ball, a soccer ball, and a basketball in a weedy field. You noticed that each ball is hollow, and each has an increasingly thicker skin. You’re really excited, and figure that each evolved from some common ancestor! Then you spend the rest of your life trying to figure out how that could possibly have happened. You invent story after story to explain that evolution, and even though the evidence is against each suggestion you make, many people believe you. They don’t seem to realize that finding the balls lined up in a particular order doesn’t prove descent at all.

If you’re spending all your time stealing equipment from PE class and trying to tell people that basketballs evolved from a tennis ball, I’d say you’ve got some rather important mental health problems. That aside, Richards’ example is yet another poor YEC analogy (I swear, half of creationist literature is bad analogy) that intimates that scientists are deluded fools that have essentially created a hypothesis and constructed a lineage to prove the ideas they already possessed. As can be seen from my earlier essay, that is most certainly not the case, and Richards’ passage is at best grossly misinformed and at worst malicious.

To be entirely honest, I was rather surprised by the overall paucity of creationist literature as pertaining to horse evolution. Given it’s prominence in textbooks and museums (and even though many books and institutions still present such evolution incorrectly) I would have expected at least a semi-rigorous creationist explanation for horses, but they seem content to merely criticize the work of Marsh and Huxley, praising Richard Owen for not associating the European Hyrcaotherium with living horses. Even in the one book (Icons of Evolution) that specifically targets horse evolution, the phylogeny is only a set up in order to allow Wells to attack Darwin and Dawkins, hinting that orthogenesis should still be considered as being a good hypothesis for evolution. If such attempts are the best that creationists can muster, I really must wonder how they have gained so much influence with such weak arguments. My question is a rhetorical one, being that pre-existing religious leanings often dictating what will be swallowed and what will be spat out when it comes to science, but perhaps the influence of creationist talking heads like Wells and Gish show just how intellectually lazy Americans have become, citizens being willing to agree with anything that won’t upset anyone during Sunday dinner after church.

As mentioned here and in my previous work, however, museums and those who write books (be they popular or for students) mentioning horse evolution are far from blameless. The “branching bush” of horse evolution is often ignored so that a general type of anagenesis from one type to another can be put forward, and this sort of technique does not serve anyone well. It will only cause confusion if presented alone, and over and over again it is apparent that evolutionary images are far more powerful than the text of any given book. While those who wish to bring about scientific understanding to the public should not let up in terms of accuracy within their writings, we must be mindful of what images we use to illustrate evolution, an inaccurate image being able to haunt educators for far longer than an obscure reference in a book. Often unintentionally, writers of popular science books and museum curators/designers have created “monstrous memes” that reproduce at an astonishing rate, persisting long after their original source material is forgotten, and if we are to be successful in getting the public to understand science, we must supplant and replace the illustrative errors of those who have come before.





The Branching Bush of Horse Evolution

13 09 2007

Note: Welcome, visitors from The Sandwalk and Pharyngula! I am certainly humbled by the amount of praise and attention this post has received, and although it’s not as scientifically rigorous as I would have liked to be (I still have much to learn), I hope that you find it to be an enjoyable read all the same.

Update: I’ve created something of an appendix to this article about how creationists have presented horse evolution in some of their books. It can be found here.

Eohippus
One of Charles R. Knight’s interpretations of Eohippus

When the name of O.C. Marsh is invoked, it is often to tell of his participation in the great “Bone Wars” of the late 19th century, sparring with fellow osteophile E.D. Cope in the pages of the New York Herald. Twisted tales of deceit and sabotage were promulgated in the sensationalist paper, and while both men helped to bring about an American revolution in vertebrate paleontology, the scars of their bitter squabbling have yet to fully heal. Such scientific in-fighting might seem worthy only of a historical footnote or an introduction to the stereotyped image of “smash-and-grab” paleontology of the time which is almost romantically referred to, but the truth of the matter goes far deeper than the public beard-pulling that is so often remembered.

The tiff between Cope and Marsh is strange in that is seems to exist in the popular literature out of time, removed from the context in which it had originally existed. Charles Darwin had published his earth-shaking work On the Origin of Species by Natural Selection a scant 31 years before the ink almost ran red with rage on the pages of the Herald, the question of evolution being of far more importance in the public consciousness than dinosaurs. The full establishment of the dinosaur as a cultural (and dare I say, mythical) creature in the mind of the American public only seemed to take place after the Bone Wars, the appointment of Henry Fairfield Osborn to the American Museum of Natural History (specifically hired to establish a vertebrate paleontology program) and the popular reports of the dinosaur that carried the namesake of Andrew Carnegie, Diplodocus carnegei, being the more immediate beginnings of the public’s love affair with the extinct creatures. Before Brontosaurus and Tyrannosaurus became household names, the public eye was focused upon horses and birds.

The latter half of the 19th century was a stirring time for biological science, especially involving the new areas of vertebrate paleontology and evolution, the august authorities in England keeping on eye on the up-and-comers starting their own careers in the states. Early on, paleontologist E.D. Cope impressed T.H. Huxley with his 1866 discovery of Laelaps aquilunguis, but in a paleontological clean-sweep Marsh would eventually have his name attached to Cope’s dinosaur and the admiration of not only T.H. Huxley, but Charles Darwin himself. As for the renaming of Laelaps, Marsh found that the name was already taken by a genus of mite, renaming the New Jersey greensand dinosaur Dryptosaurus in 1877 (although Cope, throughout the rest of his career, called the dinosaur Laelaps). It would take more than some taxonomic shuffling to impress the eminent British anatomists and paleontologists, however, and Marsh’s ticket into Huxley’s good graces came in the form of toothed Cretaceous birds like Hesperornis (Marsh, 1872).

While the discovery of ancient bones was exciting to some, evolution was an even more popular topic, and the question that surrounded every fossil was “How does this fit into the grand scheme of evolution?” The 1861 discovery of Archaeopteryx from the lagerstatten of Solnhofen, Germany seemed to arrive right on cue to confirm that evolution had taken place in times previously referred to as “antediluvial”, and Marsh’s subsequent discovery of birds with teeth in the American West further confirmed the notion that aves had evolved from reptilian ancestors (Huxley even being so progressive as to name the dinosaurs as the probable ancestral stock). Charles Darwin himself recognized the importance of Marsh’s discoveries as well, and two years after Marsh visited Darwin at Down House in 1878, Darwin wrote the following letter to Marsh on or about August 31, 1880;

I received some time ago your very kind note of July 28th, & yesterday the magnificent volume. I have looked with renewed admiration at the plates, & will soon read the text. Your work on these old birds & on the many fossil animals of N. America has afforded the best support to the theory of evolution, which has appeared within the last 20 years. The general appearance of the copy which you have sent me is worthy of its contents, and I can say nothing stronger than this.

With cordial thanks, believe me yours very sincerely,

Charles Darwin

Toothed birds were not Marsh’s only claim to evolutionary fame, however; by 1876 his assistants had collected enough fossil horse material to show that the horse was not “a gift from the Old World to the New” (as an European authority had once said during a lecture), but quite the reverse. In fact, the timing of the discovery and study of the horses could not have been better for Marsh, as in 1876 T.H. Huxley visited Yale and was duly impressed with the American Professor and his fossil horses. Huxley was absolutely enthralled by Marsh’s fossil equids, and Huxley’s son Leonard wrote of the visitation upon the New World horses as follows;

At each inquiry, whether he had a specimen to illustrate such and such a point or exemplify a transition from earlier and less specialized forms to later and more specialized ones, Professor Marsh would simply turn to his assistant and bid him fetch box number so and so, until Huxley turned upon him and said ‘I believe you are a magician; whatever I want, you just conjure up.'”

Eohippus
Restoration of Eohippus. From “The Dawn Horse or Eohippus” by Chester Stock (1947).

Huxley even featured Marsh’s discoveries of toothed birds and fossil horses in a set of three lectures he delivered at Chickering Hall in New York, the visit of such a famous evolutionist being front page news (with Marsh sharing in good press since his fossils were discussed by so prominent a figure as Huxley). The only thing that could have made the event sweeter would have been the knowledge of an ancestral horse with five toes (what was regarded as the “primitive” condition for mammals as far as digits go), and Huxley prophesied that such a creature would likely be found in North America. In truth, while it did not precisely fit the bill, a horse bearing a vestigial fifth toe had already been found and was collecting dust in Marsh’s Peabody museum. Writing to Huxley on July 12, 1877, Marsh revealed that little Eohippus (a name that was given up when it was discovered that Richard Owen’s Hyracotherium had priority, only to be later changed back to Eohippus in recent years) had been right under his nose all along;

I had him “corralled” in the basement of our Museum when you were there, but he was so covered with Eocene mud, I did not know him from Orohippus. I promise you his grandfather in time for your next horse lecture if you will give me proper notice.

Although the popular press did not take much note of the re-discovery of Eohippus, Huxley was well pleased, and promised to show Marsh all the “lions” of British science during his aforementioned 1878 visit. Such close ties would be important to Marsh later on, serving to keep Cope out of some respectable circles as well as giving Marsh a good amount of prestige. Oddly enough, however, Cope had his own horse genealogy (although ignoring Marsh’s labels) that went from four toes to one, and it was Cope’s “dawn horse” that provided the basis for some of the first Eohippus reconstructions, not Marsh’s. While Cope missed out on a golden opportunity in 1872 when he was provided a jaw fragment of an early horse, Marsh’s skeleton (as far as I can tell) remained locked away while Cope’s employee J.L. Wortmann uncovered the rest of Cope’s specimen of Eohippus in 1880. Cope named his animal Protorohippus, and it was his reconstruction that ultimately influenced Charles R. Knight and, subsequently, Rudolph Zallinger when he painted his famous Age of Mammals mural. For those who did not get at least a chuckle out of the last line, Zallinger created his mammalian masterpiece for the Peabody museum, the very establishment that O.C. Marsh had created to start his professional career.

As can be said of any scientist, however, Cope and Marsh were both products of their time and (especially in their respective cases) their egos, and while the fact that horses evolved was proved beyond doubt, both men made mistakes when it came to evolution. While Cope, late in his career, bemoaned the fact that Marsh had poisoned the well when it came to making connections with Huxley and other British scientists, it is doubtful that Cope would have lasted long amongst those of the Darwinian school of evolution. In the 1896 book The Primary Factors of Organic Evolution, Cope saw the evolution of the horse being orthogenic, or proceeding in such a way as to imply direction towards a more adapted or perfected form. As this concerns horses, Cope wrote;

Examination of all these genealogical lines reveals a certain definiteness of end and directness of approach. We discover no accessions of characters which are afterwards lost, as would naturally occur as a result of undirected variation. Nor do we discover anything like the appearance of sports along the line, the word sport being used in the sense of a variation widely divergent from its immediate ancestor. On the contrary, the more thorough becomes our knowledge of the series, the more evident does it become that progressive evolution has advanced by minute increments along a definite line, and that variations off this line have not exerted an appreciable influence on the result.

Such notions would have gotten Cope banned from Finch’s Beak gentleman’s association (if one had actually existed), the concept of directed evolution undermining one of the most important points that Darwin had attempted to make about the “transmutation” of life on earth. As we shall later see, however, such notions of orthogenesis may have had some influence on one of Cope’s latter-day pupils, Henry Fairfield Osborn, as well.


An illustration of the horse “Clique,” which had an extra toe on each fore-foot. Marsh examined this horse while still alive, and the horse was donated to Yale after its death in 1891. From Marsh, O.C. 1892. “Recent Polydactyl Horses.”

Marsh, as has already been determined, definitely had the attention of the progenitors of evolution by natural selection, and through the efforts of Matt Wedel, Randy Irmis, and Mike Taylor a number of Marsh’s writings have become available for viewing on the internet (The Marsh Repository). In a 1879 paper published some time after Huxley’s visit, “Polydactyle Horses, Recent and Extinct,” Marsh prefaces the rather short fossil section with several pages about known horses within recent history that had extra digits. The most typical condition for the differing equines was having an extra digit on the inside of the front hooves, one that did not touch the ground. Coupled with a brief appeal to similar observations of extra toes from development, this approach was indeed a wise one; not only do most living horses have vestiges of digits that have been lost, sometimes a multi-toed condition still occurs in living animals, seemingly fitting with the same trends seen in extinct genera.

Marsh's Geneology of the Horse
O.C. Marsh’s concept of “The Geneology of the Horse,” a decidedly straight-line progression. From Marsh, O.C. 1879. “Polydactyly Horses, Recent and Extinct.”

What is notable about Marsh’s interpretation of the history of horse evolution is how straightforward it is. Although missing Cope’s differing evolutionary hypotheses, Marsh makes no qualifications about the fossils he found representing only the “types” of different horses; horses evolved along a straight line, and while a few steps may be missing, it was not indicative of the widely branching pattern recognized by later scientists. The “extraneous” toes seem to become reduced in a gradual fashion, while size and tooth height increased (although the patterns on the teeth, as can be seen in the illustration, vary quite a bit in the “higher” forms). Perhaps Marsh’s adherence to a strict linear progression was at least partly inspired by the diagnosis of Huxley. In an obituary written by Marsh to commemorate Huxley’s life, Marsh made special mention of his horses;

One of Huxley’s lectures in New York was to he on the genealogy of the horse, a subject which he had already written about, based entirely upon European specimens. My own explorations had led me to conclusions quite different from his, and my specimens seemed to me to prove conclusively that the horse originated in the New World and not in the Old, and that its genealogy must be worked out here. With some hesitation, I laid the whole matter frankly before Huxley, and he spent nearly two days going over my specimens with me, and testing each point I made. He then informed me that all this was new to him, and that my facts demonstrated the evolution of the horse beyond question, and for the first time indicated the direct line of descent of an existing animal.

Such interpretations of evolution and the fossil record could only exist within a certain paleontological framework; the more bones that were found from different times and locales the more the old notions would splinter and crack. Vertebrate paleontologists who would succeed Cope and Marsh could not study what they did not have, however, but they still recognized the importance of the horse in showing evolution to be a reality. In 1891 Henry Fairfield Osborn, an independently wealthy Princeton professor and one of E.D. Cope’s friends and supporters during the embroiled Herald fiasco, was appointed the first curator of vertebrate paleontology at the American Museum of Natural History in New York City. The museum was somewhat embarrassed at not possessing any sizable collection of vertebrate fossil material, and even though Cope eventually sold some of his collection to the AMNH for a sum that disappointed the beleaguered Philadelphian, the halls of the great institution were still found wanting of ancient creatures that would bring it notoriety.

Osborn, despite his off-kilter ideas about human evolution that plagued his later years, largely made the AMNH what it is today, having some of the best and brightest collectors and preparators of the 20th century under his employ. While such gems as Barnum Brown’s two Tyrannosaurus rex skeletons, the specimen that remains on display today being Brown’s self-confessed “favorite child,” definitely helped to make the museum famous, some of Osborn’s favorite subjects were the fossil horses. Early on in his career, Osborn attempted to raise $10,000 from museum trustees for a project involving horse evolution, but the appeal was denied. Osborn kept at it and eventually succeeded, however, securing $15,000 from William C. Whitney in 1897, funds used to send collectors and curators like James W. Gidley, Bill Thomson, W.D. Matthew, and Walter Granger out into the field to collect ever more horses from Texas, South Dakota, Colorado, and other locales. Indeed, Osborn soon had many new horse fossils to study and display, creating one of the most notable (and among Biblical fundamentalists, controversial) displays of evolution ever presented to the public.

*(WWII caused the museum to send the first, more incomplete Tyrannosaurus rex skeleton, to the Carnegie Museum out of fear that the museum would be bombed and both would be lost. This may seem like an ill-founded fear, but many fossils like Spinosaurus were lost because German museums were struck with Allied payloads.)

Osborn did much to enhance the AMNH collections during the close of the 19th century, although his rather strange views about mammalian evolution (fueled in part by racism and part by Osborn’s membership in the Presbyterian church) never found wide acceptance. Despite his pet hypotheses, Osborn sent paleontologists far and wide in search of specimens to confirm his ideas, and at least in the case of the Roy Chapman Andrews expeditions during the early 1920’s, unexpected boons abounded. While Marsh held that he had moved horse ancestry out of the Old World and safely into America’s domain, Osborn saw the origin of major placental mammalian groups stemming from Asia (including the origin of humans), the hypothetical five-toed ancestor of the horse remaining elusive in North America because it was “really” buried somewhere in Asia. Osborn described his hypothesis as follows;

In the dispersal center, during the Age of Reptiles and the beginning of the Age of Mammals, there evolved the most remote ancestors of all the higher kinds of mammalian life which exist today, including, for example, the five-toed horses, which have not yet been discovered in either Europe or America. That the very earliest horses known in either Europe or America were four-toed indicates that their ancestors may have lost their fifth toe while still resident in the Asiatic homeland.

Roy Chapman Andrews did not bring Osborn any Asiatic five-toed horses from the expeditions into Mongolia in the early 1920’s, although the mammals Paraceratherium and Andrewsarchus were exciting enough in and of themselves. .

The lack of the most ancestral mammalian fossils did not stop Obsorn from attempting to further his own hypotheses, however, and in order to understand how straight-line evolution may have been presented at the AMNH we need to know how Osborn obfuscated the role of “chance” in evolution (using it almost in the same context as modern creationists do), calling the idea that natural selection works on random variations a “dogma.” Osborn instead preferred an Aristotelian “law,” quoting the philosopher in his 1917 book The Origin and Evolution of Life;

So far as law is concerned, we observe that the evolution of life forms is like that of the stars: their origin and evolution as revealed through palaeontology go to prove that Aristotle was essentially right when he said that “Nature produces those things which, being continually moved by a certain principle contained in themselves, arrive at a certain end.”

Such a notion could be regarded as the “Restless Gene” hypothesis, with what Osborn then referred to as the “hereditary-chromatin” in the animal filling needs as they arose in order to achieve a particular end. Despite his confusion about the role of “law” and “chance” in nature, Osborn did recognize that there were certain ratios in limb structures that were present in animals filling different ecological niches, even closely related ones. In the same book, Osborn writes the following about early horses;

No form of sudden change of character (saltation, mutation of de Vries) or of the chance theory of evolution accounts for such precise steps in mechanical adjustment [as in the limb structure of horses]; because for all the proportional changes, which make up ninety-five percent of mammalian evolution, we must seek a similar cause, namely, the cause of acceleration, balance or persistence, and retardation. This cause may prove to be in the nature of physiochemical interactions regulated by selection. The great importance of selection in the evolution of proportion is demonstrated by the universal law that the limb proportions of mammals are closely adjusted to provide for escape from enemies at each stage in development.

This chain of reasoning, such as it is, nearly works backwards from evolution’s “products” (which it is never done fiddling with), much like the lampoon (which I believe stems from Voltaire, although I have been unable to find the quote) that the nose was placed on the human face to hold up ones glasses.

Equus scotti
Assemblage of bones, illustrated as discovery in situ, of the Pleistocene horse Equus scotti. From Gidley, James Williams. 1900 “A new species of Pleistocene horse from the Staked Plains of Texas“. Bulletin of the AMNH ; v. 13, article 13.

Equus scotti
A mounted skeleton of Equus scotti at the AMNH, constructed out of two skeletons. From Gidley, James Williams. 1901. “Tooth characters and revision of the North American species of the genus Equus.” Bulletin of the AMNH ; v. 14, article 9.

Even though Osborn’s ideas of evolution did not catch on, the idea of horse evolution as a more-or-less straight line was still a popular one, at least in works and representations meant for public consumption. The diversity of fossil horses, thanks to many of the expeditions undertaken by Osborn’s department at the beginning of the 20th century, had considerably expanded, and the idea of an evolutionary “bush” for horses began to take root. Such a representation can be seen in one such generalized and “primitive” bush provided by J.W. Gidley in a 1907 paper on horses from the Miocene and Pliocene of North America. Indeed, the diversity of three-toed forms suggested that ancestry was perhaps more complicated than previously thought, more than one form of horse existing at any one time depending on the available habitats. Osborn noted this in his 1917 book as well, but it seemed to be only a supplementary bit of information behind his ideas of a biogenetic law. One of Osborn’s hires, J.W. Gidley, had a more accurate view of horse evolution, however, and produced the first known branching phylogeny of horses through the Miocene and Pliocene.

Old Horse Evolution Tree
A hypothesis as to the relationships of horse subfamilies by J.W. Gidley in 1907. This is the first known branching diagram for horse evolution. From Gidley, James Williams. 1907. “Revision of the Miocene and Pliocene Equidae of North America.” Bulletin of the AMNH ; v. 23, article 35.

As can be seen from Marsh’s earlier phyletic progression, much of horse evolution seemed to be dictated by features of teeth, the number of toes, and certain aspects of the skull, but as Gidley notes in his paper more material is needed if we are to truly understand the relationships of horses. Indeed, things were not so clean and neat as implied by Marsh’s illustration, even with the inclusion of new taxa. In the summary of the research, Gidley concludes;

As at present understood, the fact seems to be fairly well established that there is a considerable phyletic hiatus between the groups of the Equidae as above subdivided, which are as yet not bridged over by intermediate forms. Such a hiatus seems especially marked between the Anchitheriinae and the Protohippinae, while these groups greatly overlap each other in time. So far as indicated by any known species the Anchitheriinae could not well have stood in direct ancestral line to the latter group or to the Equiinae. There seems also to be almost as decided a gap between the Anchitheriinae and the known species of the older group, the Hyracotheriinie. The Equiinae may well have been derived from some species of the Protohippus division of the Protohippinae.

Outside of engaging in a more detailed study, Gidley also made note that various genera of horses overlapped in time with each other. While this does not rule out anagenesis entirely, it is a problem if there is such a large diversity of horses with similar features living alongside each other rather than a few isolated populations moving in a straight-line progression. The overlap was recognized and illustrated by W.D. Matthew almost 20 years after Gidley’s paper, showing where and when fossil horses existed;

Geological and Geographic Range of Equidae
Visual representation of the geological span and geographical ranges of equids through the Cenozoic. Such a representation could easily be misunderstood as endorsing straight-line evolution of horses. From Matthew, W.D. 1926. “The Evolution of the Horse: A Record and Its InterpretationThe Quarterly Review of Biology, Vol. 1, No. 2., pp. 139-185.

While the illustration, if followed closely, does show a branching pattern of evolution, to an untrained eye the evolution of horses through time seems to go in a relatively straight line, the overlap seemingly giving way to an almost orthogenic trend. I doubt that Matthew’s article was regular Sunday night reading for families of the late 1920’s and so I doubt that it contributed directly to mistaken notions of horse evolution, but another illustration from the same paper could more easily cause confusion;

Horse Evolution Simplified
A simplified, “straight-line” version of horse evolution (Click the image for a larger version). This figure was also reproduced in George McCready Price’s The Predicament of Evolution. From Matthew, W.D. 1926. “The Evolution of the Horse: A Record and Its InterpretationThe Quarterly Review of Biology, Vol. 1, No. 2., pp. 139-185.

This model is similar to Marsh’s (see above) in that horses seem to have followed a very simple ancestor/descendant progression through time. While it is true that living horses did have ancestors with multiple toes and we could trace their line backwards through time to the exclusion of other closely related genera, diagrams like this one seem to have “won out” in the public mind over those that more fully encompassed horse diversity. A 1940 paper by R.A. Stirton would be much clearer when it came to the branching horse lineage;

Stirton Horse Phylogeny
From Stirton, R. A. 1940. Phylogeny of North American Equidae. Bull. Dept. Geol. Sci., Univ. California 25(4): 165-198.

Stirton’s illustration is interesting as it shows a fairly straightforward line of descent through Miohippus is the Upper Oligocene, Miohippus giving rise to some side branches that would eventually go extinct before modern times. The radiation of the ancestors and close relatives of modern horses did not start, according to the phylogeny, until the Upper Miocene and Merychippus, Pliohippus eventually giving rise to Equus in the Upper Pliocene. Further, it is interesting to see how close Stirton’s phylogeny is to the work of later researchers, especially that fossil horse authority Bruce McFadden;

McFadden Horse Phylogeny
From MacFadden, Bruce. 1985. “Patterns of Phylogeny and Rates of Evolution in Fossil Horses: Hipparions from the Miocene and Pliocene of North AmericaPaleobiology, Vol. 11, No. 3. (Summer, 1985), pp. 245-257.

The phylogeny is extremely similar to Stirton’s through Parahippus, but the upper branches are a bit more detailed. Instead of having the genus Equus be a descendant of Pliohippus, Pliohippus is relegated to an offshoot that goes extinct before the Pliocene, the genus Dinohippus giving rise to Equus and the recent horses of the New and Old World in that genera. We will come back to the work of MacFadden later, but it is important to note how close the ideas of researchers in decades past were with modern understanding in this area.

Quinn Horse Phylogeny
From Quinn, J. H. 1955. Miocene Equidae of the Texas Gulf Coastal Plain. Bur. Econ. Geol., Univ. Texas Pub. 5516: 102 pp. (Click for larger image)

J.H. Quinn’s 1955 phylogeny of the horses of the Texas Gulf Coastal Plain was even more wildly branching than Stirton’s, and while Quinn’s focus was a bit more narrow, the tree is much more divergent. Other researchers had the genus Equus arising in the late Pliocene (and even as late as the Pleistocene), Quinn’s version has Equus appearing as early as the middle Miocene, Merychippus, again being nominated as the progenitor of all the subsequent forms in the area. While this version of horse evolution has been extensively reshuffled and revised, it is important to note that the idea that horses evolved in a straight line was well out of fashion by the middle of the 20th century at the very latest. Why, then, did it hang on for so long in the public mind?

Mercyhippus
A mount of Mercyhippus isonesus quintus. From Simpson, George Gaylord. 1932. “Mounted skeletons of Eohippus, Merychippus, and Hesperosiren.” American Museum novitates ; no. 587

Part of the problem with museums is that it takes a lot of time, money, and effort to revise exhibitions, and for some time the American Museum of Natural History horse display (THE display that illustrated horse evolution for many years) followed a progression like that of W.D. Matthew’s simplified diagram (see above). While this was eventually changed when the fossil halls were refurbished, it still seemed to show a straight line of descent, and even the display that stands on the fourth floor of the museum today reflects such a transition. If you read the plaques and take the time to compare the skeletons the branching nature of horse evolution is apparent, but the fossils themselves are arranged from Eohippus to Equus in a two parallel straight lines, showing an overall smaller-to-larger and many-to-one toe progression. Likewise, popular books on evolution and paleontology seemed hard-pressed to let go of straight-line evidence. While it could be said that such books were correct in that we could follow the line of descent from modern horses backwards to the exclusion of other groups, this approach seems to do more harm than good in the long run. Take A.S. Romer’s Man and the Vertebrates: Vol. I, for example. Originally published in 1933, my 1954 Pelican Books paperback edition shows the fossil limbs of Eohippus, Miohippus, Merychippus, and Equus from left to right, once again giving the illusion of a pure line of anagenesis. No hint of a larger diversity is given outside a brief mention of the modern forms of Zebra, Ass, and Prezwalski’s Horse.

Eohippus to Equus
Comparison of Eohippus to Equus. There’s a lot of evolution in that dashed line. From “The Dawn Horse or Eohippus” by Chester Stock (1947).

The 1966 edition of Romer’s Vertebrate Paleontology fairs better overall, but is still found wanting. The same straight-line illustration I just mentioned is found in the section treating perissodactyls as a group, and the skeletons of Eohippus, Mesohippus, and Hippidion are shown left to right across pages 266 and 267. While the text does mention an overall diversity of forms, as well as using certain genera for the “type” from which modern horses evolved, the overall visual impression of simple anagenesis remains. Again, I doubt the casual reader picked up Romer’s book for light nightly reading, but it is strange that the progressive ideas about evolution during that time are so poorly represented.

A similar time-capsule is Edwin Colbert’s Evolution of the Vertebrates, originally printed in 1955. The 1966 edition is the one that I acquired, and it is an interesting contrast to Romer’s book. At first Colbert seems to fall into the same trappings of straight-line evolution, showing a simple progression (in text with arrows) from Hyracotherium (Eohippus) -> Orohippus ->Epihippus -> Mesohippus -> Miohippus, spanning the Lower Eocene to the Upper Oligocene. After this progression, however, Colbert does note that there was a proliferation in forms;

By the end of the Oligocene epoch the horses had through these changes attained the status of advanced browsers, capable of eating leaves and soft plants and able to run fairly rapidly and for sustained periods over hard ground. With the advent of Miocene times there was a branching out of horses along several lines of development, probably as a response to an increase in the variety of environments available to them, and especially because of the spread of early grasses and other flowering plants.

An illustration on page 364 makes something of an attempt to reflect this visually, following the phylogeny of R.A. Stirton (see above) but in a more subdued and compressed manner. Being that only the genus names are mentioned, Colbert’s tree looks especially bare, although it must be conceded that it is a more accurate depiction of horse evolution than Romer’s. The illustration on page 148 of the 1961 paperback edition of G.G. Simpson’s Horses more closely follows Stirton’s phylogeny as well, and the plates likewise show the branching of tooth shapes and other characters rather than grouping forms separated by large expanses of time. The relatively rich fossil record of horses would be important to Simpson in another way as well; in his Neo-Darwinian Synthesis-era work, Tempo and Mode in Evolution (1944), Simpson was able to conclude that horses in general seemed to evolve faster than unrelated groups of animals like ammonites but more slowly than mammals like elephants. Although his hypothesis of a near-constant, albeit accelerated, rate for horse evolution has not held up today, the idea that evolution can occur more quickly or more slowly was a very important idea, an idea that took new form in Eldredge & Gould’s hypothesis of punctuated equilibria decades later.

McFadden Horse Phylogeny
From McFadden, Bruce. 2005. “Fossil Horses – Evidence of Evolution.” Science Vol. 307. no. 5716, pp. 1728 – 1730

So what of our current understanding of horse evolution? As I had mentioned earlier, one of the foremost authorities on the topic is Bruce MacFadden, and in 2005 he authored a straightforward summation of the current state of things in an article entitled “Fossil Horses – Evidence for Evolution.” As MacFadden notes, the overall “look” for the tree, featuring lines that did not leave modern descendants, hasn’t changed much since the time of Stirton and other earlier scientists. There has been much shuffling around and plenty of new discoveries, however, and although the diversity of late horses often gets the most attention it is now being revealed that early members of the horse lineage had a wider diversity as well. It almost seems like there’s an evolutionary bottleneck during the Oligocene, with the beginnings of more diversity in the Miocene, Mercyhippus once again leading the charge on to later forms.

MacFadden also takes a moment to correct a common misconception about horse evolution; there was no unalterable progression from small to large consonant with Cope’s Rule;

Although the 55-My old fossil horse sequence has been used as a classic example of Cope’s rule, this notion is now known to be incorrect. Rather than a linear progression toward larger body size, fossil horse macroevolution is characterized by two distinctly different phases. From 55 to 20 Ma, primitive horses had estimated body sizes between ~10 and 50 kg. In contrast, from 20 Ma until the present, fossil horses were more diverse in their body sizes. Some clades became larger (like those that gave rise to Equus), others remained relatively static in body size, and others became smaller over time.

Still, our current understanding is incomplete, and further fossil finds will continue to rustle the branches of the evolutionary bush. In fact, I would not be surprised if more early forms came to light, and I would be especially interested to see if the “Oligocene Bottleneck” is real or merely a factor of fossil collecting bias. There should be no mistake about the amazing entanglement of branches horses represent, however, and it is somewhat surprising that the public does not often hear about the true form of horse phylogeny. While I did not do an in-depth study of how horse evolution was portrayed in the popular media, from what I have seen it seems that past scientists and authors have often opted for simplicity, getting the public to accept evolution has occurred being more important than giving them an accurate depiction of how evolution works. This is a harsh lesson that we are still learning, as inaccuracies in books, museum displays, and other outlets can leave the door open for creationists to spread distrust of science. It is not enough to merely present someone who is unfamiliar with evolution with our “best” example of anagenesis; if we do, it should be in context with the larger theme of unity and diversity of forms, not a throw-away that is supposed to dazzle in and of itself. The evolution of the horse, in fact, is a perfect example of evolution and can be an extremely powerful tool in education if used properly, but for whatever reason the common theme so far has been for many popular science writers and educators to fall out of the saddle.

Evolution is truly an amazing phenomenon; who would have ever conceived of a small, four-toed animal giving rise to Black Beauty? Our overall conception of “more” being better may even make such a move from four toes to one seem counterintuitive, yet the evidence (from fossils to that of development) is clear in its implications. Horses did not spring up out of the ground from the dust, nor were they “spoken into being” by an omnipotent power that decided that Adam should have a faithful steed. Every bone in their body cries out as to their past, and we are all the more enriched to understand that just like the horse, Homo sapiens is a still-changing product of a long and rich evolutionary history, too.





Mega-Post Preview

11 09 2007

I’ve been working on a brand new historical/evolutionary review post all day, and I’m sad to say it’s not yet completed. I was expecting a finished product by now, so as a substitute, here’s the first few paragraphs of the post that should give you some clues as to what I’ll be covering. I haven’t gone back to fully edit yet so please excuse any errors. I hope to have the whole thing finished tomorrow (it’s currently a little more than halfway done);

Eohippus
One of Charles R. Knight’s interpretations of Eohippus

When the name of O.C. Marsh is invoked, it is often to tell of his participation in the great “Bone Wars” of the late 19th century, sparring with fellow osteophile E.D. Cope in the pages of the New York Herald. Twisted tales of deceit and sabotage were promulgated in the sensationalist paper, and while both men helped to bring about an American revolution in vertebrate paleontology, the scars of their bitter squabbling have yet to fully heal. Such scientific in-fighting might seem worthy only of a historical footnote or an introduction to the stereotyped image of “smash-and-grab” paleontology of the time which is almost romantically referred to, but the truth of the matter goes far deeper than the public beard-pulling that is so often remembered.

The tiff between Cope and Marsh is strange in that is seems to exist in the popular literature out of time, removed from the context in which it had originally existed. Charles Darwin had published his earth-shaking work On the Origin of Species by Natural Selection a scant 31 years before the ink almost ran red with rage on the pages of the Herald, the question of evolution being of far more importance in the public consciousness than dinosaurs. The full establishment of the dinosaur as a cultural (and dare I say, mythical) creature in the mind of the American public only seemed to take place after the Bone Wars, the appointment of Henry Fairfield Osborn to the American Museum of Natural History (specifically hired to establish a vertebrate paleontology program) and the popular reports of the dinosaur that carried the namesake of Andrew Carnegie, Diplodocus carnegei, being the more immediate beginnings of the public’s love affair with the extinct creatures. Before Brontosaurus and Tyrannosaurus became household names, the public eye was focused upon horses and birds.

The latter half of the 19th century was a stirring time for biological science, especially involving the new areas of vertebrate paleontology and evolution, the august authorities in England keeping on eye on the up-and-comers starting their own careers in the states. Early on, paleontologist E.D. Cope impressed T.H. Huxley with his 1866 discovery of Laelaps aquilunguis, but in a paleontological clean-sweep Marsh would eventually have his name attached to Cope’s dinosaur and the admiration of not only T.H. Huxley, but Charles Darwin himself. As for the renaming of Laelaps, Marsh found that the name was already taken by a genus of mite, renaming the New Jersey greensand dinosaur Dryptosaurus in 1877 (although Cope, throughout the rest of his career, called the dinosaur Laelaps). It would take more than some taxonomic shuffling to impress the eminent British anatomists and paleontologists, however, and Marsh’s ticket into Huxley’s good graces came in the form of toothed Cretaceous birds like Hesperornis (Marsh, 1872).





There is a grandeur in this view of life…

7 09 2007

Gorilla
A female gorilla at the Bronx Zoo.

It is often all-too-easy to forget about the wonder that is in nature when one becomes embroiled in the culture war surrounding evolution and creationism. The battles are fought in public classrooms, sundry media outlets, and (perhaps most of all) the internet, but those who do recognize the intricacy and beauty of evolution should not forget to step back every once in a while and look at what so-inspired Darwin in the first place. Nature offers up more treasures and wonders than I could ever fully appreciate during my short tenure on this planet, and without this sense of unity and amazement science can quickly turn into a rather dry and forbidding set of mental exercises.

Aldo Leopold recognized this problem all too well. In his essay “Song of the Gavilan”, collected in the A Sand County Almanac (which should be required reading for any naturalist), Leopold tells of how bright minds are often told to ignore the “music” of nature;

There are men charged with the duty of examining the construction of the plants, animals, and soils which are the instruments of the great orchestra. These men are called professors. Each selects one instrument and spends his life taking it apart and describing its strings and sounding boards. This process of dismemberment is called research. The place for the dismemberment is called a university.

A professor may pluck the strings of this own instrument, but never that of another, and if he listens for music he must never admit it to his fellows or to his students. For all are restrained by an ironbound taboo which decrees that the construction of instruments is the domain of science, while the detection of harmony is the domain of poets.

Professors serve science and science serves progress. It serves progress so well that many of the more intricate instruments are stepped upon and broken in the rush to spread progress to all backward lands. One by one the parts are thus stricken from the songs of songs. If the professor is able to classify each instrument before it is broken, he is well content.

Science contributes moral as well as material blessings to the world. The great moral contribution is objectivity, or the scientific point of view. This means doubting everything except facts; it means hewing to the facts, let the chips fall where they may. One of the facts hewn to by science is that every river needs more people, and all people need more inventions, and hence more science; the good life depends on the indefinite extension of this chain of logic. That the good life on any river may likewise depend on the perception of its music, and the preservation of some music to perceive, is a form of doubt not yet entertained by science.

It would be a mistake to paint all practicing scientists with such a broad brush, but the danger of becoming so objective that the melodies of songbirds and the soft rushing of streams become muted is a very real one. This is strange, especially because it was from wonder that science was born, an attempt to explain what had hitherto been subjugated beneath superstition and religion as it exists, not how we may wish it to be. Still, despite the move away from superstition and natural theology, especially since the writings of Darwin came crashing into the public consciousness, religion attempts to retain a hold on “the birds of the air,” “the beasts of the field,” and “every thing that creepeth upon the earth.” In a recent post on the evolution/creationism debate, the author of the blog Doxoblogy opined;

I’ve got only this to say…looking at creation will inevitably point you to an ‘eternal power and divine nature’ that exists beyond us. Looking in Scripture will introduce this ‘eternal power and divine nature’ to you as the Creator God to whom we owe our love and worship (Romans 1:16-2:11). The God of creation is also the God of Scripture and He has a Son, Jesus.

Clearly there is a sense of awe operating here, and there are seemingly countless flash-animated greeting cards, books, videos, and other resources enforcing the notion that every aggregate of soil, blade of grass, or molecule of water practically screams that life was created by the Judeo-Christian God of the Bible. Such arguments have even become politically fashionable, allowing current presidential candidate John McCain, in an attempt to eat his cake and have it too, to say “I believe in evolution. But I also believe, when I hike the Grand Canyon and see it at sunset, that the hand of God is there also” when asked if he “believed” in evolution. Such a notion clearly points to subjective notions of beauty, as McCain did not say “When I look at a lamprey or a hagfish, I see the hand of God at work.” The overall association of God with the aesthetically pleasing could explain why Thomas Kinkade paintings, which differ so little that I can scarcely tell one from another, as a staple in evangelical Christian households. Perhaps there are some on the fringe that would prefer to think of a tapeworm or liver fluke when contemplating the glory of God, but the vast majority of creeping, crawling, sucking, oozing, and pulsating things on the planet are not generally thought of as being “first in the ways of God.” Even Darwin expressed his doubts about a Creator that was seemingly so cruel. In a famous letter to the American botanist Asa Gray, Darwin confided;

I am bewildered. I had no intention to write atheistically. But I own that I cannot see as plainly as others do, and as I should wish to do, evidence of design and beneficence on all sides of us. There seems to me too much misery in the world. I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae [parasitic wasps] with the express intention of their [larvae] feeding within the living bodies of Caterpillars, or that a cat should play with mice.

While generally forgotten today, the view that nature is filled with goodness or pleasurable things was, as far as I currently understand, put forth by William Paley in Natural Theology, one of Paley’s core beliefs being that the ability to feel pleasure (and not just pain) was evidence of a beneficent Creator. Still, the understanding that Darwin helped usher humanity, albeit kicking and screaming, into was an understanding of nature that is neither inherently good nor evil. The world is not “for” mankind just as it is not expressly for the benefit of water beetles, Cape Buffalo, or the Northern Flicker. If it were otherwise the world could perhaps divided into creatures that were “good” and others that were “evil,” but no clear distinction exists nor has it ever; attributing such labels to the world around us only speaks to our own ignorance and hubris.

Sometimes I have to wonder if those who propose to have seen God in nature have truly spent any time out in nature or studying its diversity. A poster of some far-flung locale at sunset with one of the Psalm’s printed on the bottom is not understanding nature, a motley organization of life that (try as we might) we are still very much a part of, and even the most repulsive or disgusting of creatures has a worth that does not rely on our “refined” tastes. When an animal dies, insects and bacteria take advantage of the bonanza, putrefying and decomposing the body , beginning the process that will return the creature to the earth. If special circumstances occur, it may well see the light of day again as a fossil, but more likely than not it was be completely broken up, the accumulation of energy and elements in its body being transferred into other organisms and into the ground, allowing different forms of life to flourish. This does not make a maggoty, decomposing carcass any more attractive (or smell any more fragrant), but if we divorce it from our rather superficial requirements of beauty, we can gain an understanding of nature that previously eluded us.

Perhaps my words are only those of a young man, “green” in terms of experience and landlocked in a land of impervious surface and strip malls. Such inexperience may hinder my perceptions, but when I look closely at nature I see neither angels nor demons, God and the Devil being absent from the crashing of the waves along the shore or the lighting strikes of a late-August thunderstorm. This does not mean, however, that I view nature divorced from any sense of awe or deeper emotional feeling, and I would imagine that many of my readers here would tell you the same. When I was covered in wet muck of the Inversand Marl Pit, my heart skipped a beat as a pulled out a chocolate-colored bone fragment that had been kept snug in the greensand for at least 65 million years; my mind reeled at what I could have discovered (and what else might remain buried), and I had to hold back my excitement as I asked my professor if I had really found bone or not. Any book describing the adventures and work of a more professional and seasoned paleontologist or field scientist will reveal much the same thing; objectivity is necessary for the sake of accuracy, but it often comes after a rush of excitement or amazement at a new observation or discovery.

This post is a bit of a throw-away, however, as Charles Darwin long-ago succinctly summed up the thesis of my long argument;

There is grandeur in this view of life, with its several powers, having originally been breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved. – Charles Darwin, On the Origin of Species by Natural Selection

Gorillas
A female gorilla and two babies at the Bronx Zoo








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