Friday Coelacanth

28 09 2007

Courtesy of Peter McGrath of The Beagle Project, a preserved specimen of the extant coelacanth Latimeria chalumnae from the Natural History Museum in London, England;


Photos from the AMNH (yet again)

22 09 2007

Here are a few of the photos I took today during my visit to the AMNH. I decided to be “adventurous” and take exclusively B&W shots, hoping to better convey the mood of some of the fossils (or their replicas) that I was looking at. I’ll leave you to be the judge as to whether any of them succeeded in giving more life to the old bones than I have been able to do with color photography.

The relatively gracile (at least compared to the specimen on the 4th floor, see below), yet dynamic mount of Allosaurus in the Grand Rotunda of the AMNH.

The skull of the 4th floor Allosaurus, the famous mount being bent over the chewed vertebral column of an Apatosaurus.

Skull of the “Bear Dog” Amphicyon, a member of the Carnivora from the 4th floor mammal halls. Notice the big saggital crest, the placement of the cheekbones further out from the head, and lack of bone that (while typically not closed at the back) would normally surround the eye. This creature would have had an incredibly powerful bite.

Indeed, the skull of Amphicyon reminded me of that of the creodont Hyaenodon. Again, notice the sagittal crest, the cheekbones placed further out from the skull, and the near lack of bone that would enclose the eye. While smaller than the “Bear Dog,” I still wouldn’t want to cross a Hyaenodon on a bad day.

Compare both those skulls with that of the nimravid Hoplophoneus and you’ll see what I mean. Hoplophoneus doesn’t have as prominent a sagittal crest, and although it still seemed to have large jaw muscles, there isn’t the same degree of reduction of bone surrounding the eye as is seen in the previous two mammals.

And, if you like, you can compare them further still with this Smilodon that had broken off it’s left canine. Such occurrences were likely painful, debilitating, and possibly even eventually fatal, and it makes me wonder if this one died as a result of it’s wound or if it continued to survive for some time longer (which opens up all sorts of questions).

A close-up of a more intact Smilodon.

Giant Anteater
A stuffed Giant Anteater from the Hall of Biodiversity. I much prefer photographing lives xenarthrans, however.

Apatosaurus is the first sight to grace visitors entering the Hall of Saurischian Dinosaurs.

The robust neck of Apatosaurus looms high above.

Apatosaurus print
Casts of the sauropod footprints R.T. Bird found in Paluxy, TX.

Apatosaurus from the rear.

The head of Barosaurus, held up to (perhaps literally) dizzying heights.

Barosaurus foot
One of the forelimbs of Barosaurus, held out threateningly at the Allosaurus in the first photo.

The head of a mini-reconstruction of Barosaurus.

The juvenile Stegosaurus model was pretty impressive, too.

A skull of Camarasaurus.

One of the largest self-contained “bioshpheres” I have ever seen. The little dots are shrimp.

One of the most wonderfully preserved (and in my opinion, publicly unappreciated) skeletons every found; a complete and articulated Corythosaurus with skin impressions, collected from the Red Deer River region of Canada.

A juvenile hadrosaur, probably either Corythosaurus or Lambeosaurus. I ran back and forth looking at skulls to try and figure it out, but the skull of the juvenile is slightly distorted, so (me being without access and a CAT scan at hand) I wasn’t able to confirm or deny my leaning towards my hypothesis of it being a Corythosaurus.

A reconstruction of a Deinonychus skull. I looked at the forearms of the skeleton for signs of feather attachments (as had just been announced for Velociraptor by AMNH scientists) but I couldn’t see any, nor could I get close enough to get a good look.

Outside, one of it’s distant, extant relatives took a sip from a small puddle.

The skull of the synapsid Edaphosaurus.

The toothy jaws of Elasmosaurus.

Giant Squid
The famous Giant Squid that spreads its tentacles above the Hall of Biodiversity.

The skull of Gorgosaurus, formerly Albertosaurus (although this specimen was first introduced to me as Gorgosaurus in the first place…)

Perspective on a large, iron meteorite.

One of my most favorite mounts in the entire museum; Prestosuchus.

A close-up of Triceratops.

The most popular dinosaur in the museum, Tyrannosaurus rex.

The crushing jaws of Tyrannosaurus.

A stuffed Leopard, posed over a peacock. This is another animal I would much rather photograph while living.

And last but not least, my little cat Charlotte, silhouetted against the evening light while she watched the birds outside.

It’s too early for Friday notes, or is it?

21 09 2007

Some time ago I confessed my overall ignorance when it came to pterosaurs, so I was definitely happy when a 1966 reprint of H.G. Seeley’s Dragons of the Air arrived yesterday. Being written in 1901 it’s bound to be a bit dated, and Seeley seems to focus on the European pterosaurs more than anything else, but it’ll make for an interesting and quick read. I hope to finish G.G. Simpson’s Attending Marvels and Simple Curiosity during the course of the weekend as well, which should be an easy task as I’m more than halfway through both.

I do make time for fiction every now and again, though, and I was definitely pleased to find that Terry Pratchett’s newest book, Making Money is now out. Being that Going Postal is my most favorite of the Discworld series to date, I am certainly looking forward to reading of the continuing trials and tribulations of Moist von Lipwig.

Lycaenops at the AMNH

Tomorrow morning I’ll be hopping the train with some Rutgers students to the AMNH to teach them something about Deep Time and paleontology. The Big Bang, stromatolites, fossil horses, and whatever petrified critters they take an interest in will be covered, and I am definitely looking forward to using the 4th floor fossil halls as a sort of classroom. I’ve only got them for about 3 hours, however, so I’ll have ample opportunity to run around on my own for a bit afterwards. I have to start making up my PPT presentation for next week as well, so this weekend will be a busy one. If the weather is good I want to try to visit Haddonfield on Saturday to see the site where Hadrosaurus foulkii was discovered and see if I can’t find the chocolate marl from which it came, but that might have to wait.

Finally, although it only appeared in the news reports for a quick moment, a new paper in Science seems to show evidence of feathers on Velociraptor in the form of quill attachments. Unfortunately I can’t access the journal from home, but I am not glad that I was delayed in writing about another recent feathered dinosaur in the news so I can put them together in one post. Speaking of journals, I finally was able to get someone to sign my membership form for SVP as well, and I am looking forward to receiving the Journal of Vertebrate Paleontology in the mail. My post on “wee little sauropods” is still in the works as well, but I have many more papers to read before I can be sure I’m actually making sense and not just writing fiction myself.

I don’t think muses inspired computer kiosks…

14 09 2007

Me, Edmontosaurus Mummy
The author in front of Charles H. Sternberg’s Edmontosaurus (“Trachodon”) mummy at the AMNH. Sternberg was often hard-pressed for cash, so he packed this specimen up before one of H.F. Osborn’s man-in-the-field could take a look at it. Having purchased quality specimens from Sternberg before and knowing that the specimen could very well go to another museum, Osborn decided to pay Sternberg the sum he asked for, and it proved to be a very wise decision.

“Do you want to go and visit your dinosaurs?” “Are you kidding?” comes my incredulous reply, and my wife and I climb the alternating staircases up to the famed fourth floor of the American Museum of Natural History in New York City. I can scarcely remember the details of my first visits to the museum when I stood little higher than Ornitholestes, taking a cab from Penn Station to the museum with my parents, a poster of a horse skeleton next to a human skeleton in the elevator making quite an impression on me (I recognized the human form, but I had no idea what the other one was). The rest of the museum was interesting, surely, but my young brain was only interested in one thing; dinosaurs. Even to this day, no visit is complete without at least a passing visit among the fossils (or, at least, what look like fossils in some cases), and anyone who has taken a trip to the museum with me knows I am loathe to leave without meandering through the 4th floor pathways.

My first visits took place during a time when the great fossil halls were divided by time period, the skeletal contents of the halls of Saurischian and Ornithischian dinosaurs jumbled together in the dark, musty halls of Jurassic and Cretaceous dinosaurs. Some non-dinosaurian celebrities appeared through the halls as well, a far wall of the Jurassic hall displaying the ever-impressive Dimetrodon from the Permian of Texas. What I remember most clearly, however, was the imposing form of “Brontosaurus” looming out of the shadows. Long before the renovations of the mid-1990s, the fossil halls were shadowy places, the subdued lighting casting a more “primordial” mood on the hall. I was in awe of that composite skeleton, and even though I knew it was a herbivore, the short head with large blunt teeth made me think twice about whether I would call the dinosaur “harmless” in life. It didn’t matter that the skeleton I was standing beneath did not hold up huge masses of flesh for over 100 million years; I could have sworn that I heard the behemoth breathing in that dark, dusty hall. The trackway that R.T. Bird collected from Glen Rose Texas, positioned just under the feet of the giant, further gave the impression that it had just walked out for its daily viewing, perhaps waddling back into one of the storage rooms where it went to pieces at night. If I had believed in ghosts, I would have sworn that one of the restless spirits had lumbered all the way over from the Howe Quarry assemblage in Wyoming, taking possession of the skeleton but never getting a bite to eat as the paleontologists hadn’t had the presence of mind to bring some “fossil fuel” in the form of petrified leaves and ferns for poor Bronty to eat.

An archival image of “Brontosaurus,” posing in the older fossil halls before the first renovation during the era of R.T. Bird and Barnum Brown. This was the skeleton that so awed me as a child, although the setting in which I first saw it was a bit darker.

I’m sure that I saw the impressive Tyrannosaurus and Triceratops in the Cretaceous hall, and I faintly remember seeing some of Charles R. Knight’s fantastic murals that I had only seen miniaturized in so many children’s books (you really must see them blown up to their true size, or at least in high resolution; so much of the vibrance is lost in many books that have reprinted the paintings), but it was the Jurassic Hall that made the biggest impression on me. The life-size Blue Whale downstairs filled me with a sense of astonishment as well, and it was hard to believe that anything could possibly have been that big or that such creatures still swam in the oceans. Unfortunately, I did not get to visit the museum again until about 2002, mostly because of a general unease about New York City that my parents possessed and subsequently instilled in me as well. The dinosaurs were still there when I returned, even in greater number than before, but things were not how I remembered them.

A crested pterosaur hangs over the distal portion of the Hall of Vertebrate Origins at the AMNH.

The fourth floor of the AMNH, containing its fabulous vertebrate fossil collections, was entirely renovated between 1994 and 1996. In addition to “Brontosaurus” getting a name change, a new head, and an extended tail, the halls were reorganized according to cladistics and opened up to the sunlight, great windows throwing plenty of light on the stark white walls. Indeed, rather than organizing the fossils by time period, as had been the tradition previously (a tradition of grouping by convergent structures being an even older European tradition, as in Cuvier’s museum), the curators and designers decided to group the fossils according to their evolutionary relationships, creating something of a path for visitors to walk through. In addition to this, various computer kiosks featuring video explanations of many of the fossils were installed, adding a new level of “interactivity” to the exhibitions. Despite all this reshuffling of old bones mounted on armatures, however, I can’t say that I especially like the newer layout.

Anyone who regularly visits this blog knows how much I enjoy my visits to the AMNH, but my familiarity with the institution has also made me a bit critical of it as well. While I do have my gripes about the Hall of Biodiversity exhibit and the sorely out-of-date Hall of North American Mammals (it is now so old that I don’t know whether the laugh or cry when I read the labels of many of the animals presented in the dioramas and reflect at the current state of their populations in the wild), the fossil halls do the most to inspire and irk me simultaneously, and much of what I have to relate deals with the great osteological collections.

Note: If you want to follow along, the floor plan is available online.

While I can understand the reasoning behind organizing the exhibits in terms of derived characters, the approach quickly goes to pieces and seems to be above the heads of many of the visitors. The first section of the fourth floor, the Hall of Vertebrate Origins, does an acceptable job at branching off along a main path into different groups of vertebrates, acting something like a progression through time as well (at least until the end where turtles, phytosaurus, crocodilians, mosasaurs, pterosaurs, plesiosaurs, etc. are all grouped closely together). The primary problem I have with this sort of set up (which is the same problem I usually have with cladistic trees) is that everything ends abruptly in a cul-de-sac, giving the viewer no indication of whether the group continued, went extinct, or who the direct ancestors were. Location in terms of both time and place are ignored, and while this may be able to be understood by the more scientifically-informed visitors, I don’t think it presents the best understanding of evolution to those generally unfamiliar with the topic.

A head-on view of the reproduction of Deinonychus in the Hall of Saurischian Dinosaurs.

Things start to get shakier once we leave the Vertebrate Origins hall. Although I don’t usually follow this route, the path directs the visitor towards the Saurischian Dinosaurs, the theropods Tyrannosaurus and Allosaurus dominating this hall. Apatosaurus is sequestered (even coralled) up against the wall, still frozen in its tracks, but visitors can not get anywhere as close to it as I could in earlier years. This hall leads the visitor to the Ornithischian dinosaurs, Stegosaurus, Triceratops, and Anatotitan giving their imposing presence to the hall. These dinosaurs didn’t seem to get the same refurbishment as the Saurischians; poor Triceratops is still holding its front limbs out at 90 degree angles in a “super sprawl” pose, and the Anatotitan pair still have tails that would have had to be broken in order to make them droop in the manner that they do.

The Ornithischian dinosaurs give way to “Primitive Mammals,” although Dimetrodon, Edaphosaurus, Lycaenops, and other Permian forms are the main representatives in the first half of the hall, the second half being a mish-mash of various unrelated genera and xenarthrans like giant ground sloths and glyptodonts. The Milstein Hall of Advanced Mammals follows, starting off with early primates like Notharctos to the right, saber-toothed cats and other unrelated convergent forms to the left, the pathway proceeding through titanotheres, sirenians, and other groups before culminating in the impressive mammoth and mastodon skeletons at the end (be sure to look carefully around the feet of the mammoth; there is quite a surprising specimen of a baby mammoth’s skin in a glass case).

Barnum Brown T rex
“Mr. Bones”, Barnum Brown, posing with his “favorite child” in the old Cretaceous Dinosaur hall at the AMNH.

The chief problem of the plan for the 4th floor is that the the layout of the museum does not allow for a neat phylogentic layout, barring the proper grouping of the vertebrates. The four halls create a square around the central area, and the visitors has to walk through various groups before coming to the next-of-kin in terms of evolution, the halls still giving the visitor the impression of moving through time (especially since most, if not all, the mammals exhibited lived after the demise of the dinosaurs). I think it would have been much better to stick to the old system of time periods but to somehow code or tag each group (maybe by putting them in corresponding sections of each other) so that visitors could follow who was related to who through time. Regardless of how it is done, however, the set up will be tricky as the fourth floor currently occupies all the space it is ever going to have, and being that it is already so densely packed with skeletons it is hard to conceive how future renovations might bring in new specimens while keeping the “classics.”

The feel of the exhibits is also different from how I remembered them. Originally there was a more relaxed tone, visitors being allowed to get very close to the specimens, giving you the feeling that you were really under the feet of dinosaurs. I can see how this can be a problem for security/safety/janitorial reasons (lots of garbage and debris often ends up under the mounts), but now visitors are kept at arms length from specimens by glass or other barriers. It no longer feels like the fossils are part of a common heritage, something that everyone has a right to observe and learn from. Instead, it feels like we’re being allowed a look at the fossils, specimens that we have no claim to. This correlates with a major shift in paleontology that has taken place in the last 50-75 years; fossil studies have increasingly come into the fold of “good” science, and it is doubtful if the bone sharps of old could have contributed what they did to science if they were born today. Where amateur collectors and those who possessed an interest and passion for fossils once built up the fossil halls and the science of paleontology, non-professional workers are often scorned or looked down upon today, and there are often battles between what is publicly owned, what is privately owned, and what should be done with fossils that are not in the hands of museums or universities. Regardless of where you stand on this issue, the AMNH halls reflect a step away from public access, I feel, making the bones some more cold and distant, objects to be studied but not really appreciated. The lighting probably affects this more than anything else from my perspective; the lack of contrast and shadow removes much of the mood, and it is harder to imagine the animals as they would have been in life when harsh light is thrown upon them. I much prefer the set up of the Royal Tyrell Museum near Alberta, Canada, the dinosaurs there taking on a life of their own in the shadows (click here and view the see two virtual tours to see what I mean).

So what of the computer kiosks? The fourth floor has a few kiosks here and there with a guide-ball and computer screen, users being able to click on various creatures or nodes on a cladogram to get more information. This is not a bad idea in and of itself, allowing those who are interested to learn something more, but it doesn’t seem to be a big hit. Children often think the screens should allow them to play some sort of computer game, and I have seen far more rapid and irritated clicking than attentiveness whenever a child has used one of the computers. The computers are also relatively slow, taking a good amount of patience, and when they’re working it is sometimes hard to hear what the person on the video screen is saying. I’ve learned a thing or two from the video kiosks, but overall they were not very exciting or interesting, and I don’t think they appeal the younger audiences at all (and if you’re talking about dinosaurs and can’t interest kids, the adults probably won’t be any more intrigued by a discussion of why theropods have so many holes in their skulls).

I had mentioned games just a moment ago, and from what I have seen from my last visit to the Philadelphia Zoo, educational games seem to work better to interest visitors to an extent. The game I checked out myself, which seemed to be fairly popular, was one at the Big Cat Falls exhibit, the user playing a Jaguar in the southwest of the United States. The goal was to direct the Jaguar step by step to migrating across an area while eating food but not getting shot by ranchers, each step taking a moment to explain why the big cats are rare in the U.S. Not everyone will stop and play, and it’s not the ultimate answer (I am somewhat ill-at-ease with the concept of children coming to a natural history institution to play video games), but it is still better than many other displays that I’ve seen.

Part of the problem is that “interactivity” has typically translated to “computers” for many museum designers, while I think the best answers as to how to get guests involved are far more low-tech. I recently had a discussion with a friend of mine who is working with a museum on an exhibition, and she had proposed setting up a battery of microscopes in order to allow children to look at various specimens first hand. This was shot down as being too risky/expensive because someone would have to be there supervising the children. Another idea of having a visible chick incubator so that children could see the animals being born was rejected as well, and giving children little cups with some seed so they could grow a plant at home was also turned down. As my friend and I agreed, these were the sort of things that drew us into science when we were young, being direct observers to something amazing that cannot be reproduced by computers.

Even beyond the aspect of computers, I am a bit saddened to see so many artifacts and fossils on display that are replicas rather than the genuine articles. Early exhibitors did a lot of damage to wonderful specimens by drilling holes in them in order to fit them onto metal armatures, but I feel like my experience has been cheapened when I look at a skeleton and I know that it’s only a replica. Great care should be given to the bones and they belong to the generations after me as well (it would do us little good if putting something on display helped cause its destruction), but I know I’m not alone in this sentiment. In fact, this is likely part of the reason why “Lucy” is touring the U.S.; almost every major museum has a cast or replica of the famous australopithecene, but the actual skeleton that came out of the ground is something of a scientific sacred relic, and I know that when Lucy is in New York I’ll “pay my respects.”

Bones don’t even have to be put permanently on display in order to make an impression; the Page Museum, which handles the La Brea Tar Pit fossils, has a lab with a panoramic window that lets visitors see what the researchers are doing. This is a very simple thing, but I think that every major museum should have a similar facility that lets visitors look in on the work being done, and if workers can take some time out to answer questions or give a little talk, all the better. (The Academy of Natural Sciences in Philadelphia has a smaller, but far more cozy open fossil workbench, too). Open labs allow the public an look into what paleontologists really do, and I really feel that it is a shame that more museums do not scientifically open themselves up to the public in a similar way.

Everything is not as harmonious behind the scenes as one might be led to surmise, as well. Often curators bang heads with designers, mini-battles being fought over what to include and what to leave out, exhibits being subject to an editing process just like films or books. Author Stephen Asma, in the book Stuffed Animals and Pickled Heads, relates such an experience through a conversation with Dr. Eric Gyllenhaal of Chicago’s Field Museum as he tried to design the Life Over Time exhibit;

“…I have to say I’m not really impressed with having the scientists in on weekly meetings, because an inevitable part of any exhibit is that you have to trim the content down to what people will actually look at in the time that they have available to go through the entire museum. But this trimming is a very painful process for the scientists, and they tend to obstruct the process; and I say this even though I myself have a Ph.D. in geology. There are limits to what you can accomplish within a museum exhibit if you’re thinking about what you can accomplish with a normal visitor. The scientists wants to have way too much information included; it’s overkill.”

Eric started laughing and impersonating the curators. “‘You can’t leave that out, you can’t leave this out,’ or ‘This is too important an idea, you’ll be confusing people by leaving it out’-that kind of thing is endless. The scientists who consulted with us on ‘Life over Time’ for example, browbeat us with their buzzword, content. ‘You’re leaving out the content,’ they would shriek. And, of course, the content tends to be what people fill textbooks with, and textbooks these days are a thousand pages long. We like to pretend that students read these information-overload textbooks and get something out of it, but, you know, it doesn’t really happen that way. Even in college! But even though many of these curator-scientists have taught college, they haven’t caught on to this fact.”

Not everything is the fault of museum curators or designers, however. Those who visit natural history museums are responsible for their own education (or lack thereof) too, and you will only get out of a museum what you put into it in terms of attentiveness and a thirst for knowledge. Much like zoos, however, natural history museums are primarily a visual feast, a place to go and look more than anything else. David Quammen describes such a role succinctly in his essay “The White Tigers of Cincinnati”;

What is a zoo? Most essentially, it’s an arena of the visual. It’s a place to see wonders. The act of seeing is the primary zoo experience – whereas learning, thinking, and emoting are dimensions of encounter that come secondarily, if at all. We go there to look; in passing, we read a few labels and placards, of which the information content is low.

If you sit long enough to “people watch” at a museum (or a zoo), Quammen’s thesis seems all too apt. People go to see dinosaurs and move along without reading much because they already “know” what dinosaurs are; they’ve heard about them in school, seen them “come to life” in movies, bought models and toys, etc. The visit to the museum is a trip to see the animal life size, as close as we’re likely to get, and unless there’s a deeper desire for more knowledge “looking” is as far as it often goes. For now I’ll bypass the idea that dinosaurs are somehow childish and do not merit more comprehensive understanding by “proper” adults, but natural museums should appeal to the inquisitive child in all of us if they are to be effective at all.

Such desire for understanding is not always encouraged or rewarded, however, especially in a hustle-and-bustle world of deadlines and field trips. If you watch any group of schoolchildren visit the fourth floor of the museum, you’ll usually see one or two who are inordinately fond of the skeletons on display. They are not allowed to linger to indulge their curiosity, however, as they are told to keep up with the class, bumping into their classmates because they’re continually looking over their shoulders as they leave the museum. Indeed, it seems like curiosity is only allowed as long as it does not interfere with itineraries and the projected lesson plan. This is sad, especially because as the children get older and can move off on their own through the museum (typically in high school) they will probably show less interest in the things that so enthralled them when they were younger.

Museum shops can do some damage as well, and I am often surprised at the inaccurate models and toys being sold to children by various establishments. I have a Tyrannosaurus bobble-head on my desk that appears to be plantigrade, with a tail that for some reason is drooping onto the ground, and a head held up like that of a startled chicken. This is not the image of the carnivorous dinosaur depicted in the fossil hall, so why is it fit to pass off to children? Other souvenirs feature dinosaurs from all different time periods lumped together as if Jurassic Park had just let out for the weekend, and while I might seem like a crank in complaining about this, I wonder what sort of message it sends about 1) the role of scientific accuracy in museums, and 2) marketing in museums. Almost any item even bearing the image of a dinosaur is bound to bought by someone, and it often seems like the more dinosaurs there are on a product the better. Given that the most famous ones live in entirely different time periods, the presence of the dino-celebrities is more important than reflecting the ecology of one time period or another.

I really do worry about the present state of natural history museums. When I walk the 4th floor of the AMNH, I usually have a general idea of who dug up what and when, being able to spot what has changed since the displays were put up and what is still accurate. Most people don’t have the same background as I do, though, and I can only imagine what they’re getting out of the displays. We all bring out our understanding of nature to natural history museums, our prior knowledge directly influencing our experience. Last February, for instance, I stood in front of an ungulate bone bed section, a jumbled mass of mammal bones preserved under glass. The woman next to me said to her companion “Oh, I’ve heard about this. This is evidence for The Flood, right?” before moving off. She didn’t read the placard, nor did she study the assemblage; all she did was recognize a potential example of something she heard or read at one point or another and moved on. Maybe it’s because I’m a pessimist, but I feel that many visitors to natural history museums do the same thing, merely taking in the familiar but paying little attention to detail.

How can we save our natural history museums? Times are pretty tough right now, staff layoffs being common and some museums, like the aforementioned Academy of Natural Sciences, which recently sold off parts of its mineral collections in order to keep the doors open. The famous and nearly-complete Tyrannosaurus “Sue” was purchased by the Field Museum in Chicago for $7.6 million dollars after it went up for auction, but not without help from the California State University system, Walt Disney Parks and Resorts, McDonald’s, Ronald McDonald House Charities, and a few donors, part of the deal being a McDonald’s being placed in the museum (as well as the fossil prep lab being called the “McDonald’s Fossil Preparation Lab”), a cast being made for Walt Disney World’s Animal Kingdom Park, and two more casts going on a traveling tour put on by McDonald’s. Even beyond such deals, corporate logos are starting to sneak into natural history institutions, the big cat exhibit at the Philadelphia Zoo being named the “Bank of America’s Big Cat Falls” with a big Bank of America logo at the entrance, whereas previously corporations were relegated to a name on a list of donors made available to those inquisitive enough to ask for the list. As some have predicted, I have the feeling the corporate sponsorship (even ownership) of natural history museums will become a bigger problem in the coming years, and museums may go from research institutions to huge curiosity cabinets, being more about displays and making money than learning. Such an event occurred just recently in my own state, in fact, the New Jersey Aquarium in Camden changing over into private hands and becoming a for-profit institution under the new moniker of Adventure Aquarium, education being secondary to sensationalism.

I sincerely hope that we do not lose our natural history museums. Speaking for myself, I know I probably would not be as interested in evolution and paleontology if it was not for early visits to the AMNH, and I know there have been many much more intelligent and prominent scientists like Stephen Jay Gould who can trace back their own feelings of wonder to the 4th floor fossil halls. Small, home-grown institutions like the Museum of Osteology and the Black Hills Museum of Natural History offer some hope, continuing a tradition put forth by many paleontologists from the turn of the 20th century, but such institutions are usually small and difficult to reach. Even if the larger natural history museums never fully decline and the great dinosaur skeletons remain, we should work hard to promote responsible, accurate, and interesting representations of the history of life on earth, as it is possible for the history of an institution to overtake its intellectual mission of enlightenment, towering masses of bones collecting dust and being petrified in the position of their last revision from ages before.

[The preceding rant was inspired by this rant]

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.

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.'”

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?

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.

Love/Hate relationship with the AMNH

12 09 2007

I’m still picking away at fossil horses in the hope that I’ll be able to get something up tonight, but in the meantime check out Matt’s post on Natural History museums (and all the “interactive” doodads that are all the rage in major institutions these days). As is easily apparent from this blog, I absolutely love natural history museums, but there often seems to be as much that annoys me about them as attracts me to them.

Tyrannosaur Teaser

4 09 2007

I know pickings have been a bit slim here over the past few days; I’ve been in a bit of an intellectual funk (especially yesterday) and have been wrapped up with the beginning of the semester. Still, I am still writing, and I’ve got something good cooking that I think many of my readers will enjoy quite a bit. Here’s the preliminary introductoray paragraph from a forthcoming monster post about one of my most favorite Cretaceous carnivores;

Tyrannosaurus AMNH

Never has there been a more frightening visage to grace the hallowed halls of the 4th floor of the American Museum of Natural History than that of Tyrannosaurus rex. I could not help but be awed and terrified by the post mortem articulation of bones of the what seemed to be the apex of dinosaur evolution during my first visit to the great fossil gallery. It didn’t matter that the monster was standing upright, dragging its tail along the ground and dangling its dainty arms feebly in the air, the long-dead dinosaur seemed as alert and ferocious as it must have been in life, as if it was rearing up to its full height in search of small, warm-blooded, 10-year-old Homo sapiens for a snack. Mouth agape, serrated fangs glistening in the sunlight filtering in through the dusty windows, it was hard to turn away from the remains of the last great predator of the Mesozoic, partially out of awe, partially out of an overactive imagination that saw the bones removing themselves from their metal supports to start stomping down the walkway towards scores of hapless visitors. Staring at the magnificently grotesque form I realized that my parents had lied to me; monsters were real, even if the gulf of time kept me safe from their bone-crunching maws.


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