Saturday notes

30 06 2007

I’m afraid I probably won’t be writing any long or especially informative posts today. Earlier I visited to zoo where I had a chance to feed the giraffes and see a number of other animals (pictures will be up as soon as I get transfer them to the computer), and I’ve spent my time since trying to finish off A Primate’s Memoir. This evening looks booked up as well, but hopefully tomorrow I’ll get to share a bit of what I learned (or at least transcribe some thoughts about Sapolsky’s excellent book).

My wha?

29 06 2007

Good news everyone! I got the wireless connection to work at the house I’ll be staying in for the next week (+), so you can expect plenty of new material as I try and dig myself out of the avalanche of books I’ve brought upon myself. Tonight, however, I’m going out to see Ratatouille; I can never say no to a Pixar feature.

Two Extinct Birds Seen Again

29 06 2007

Just in case you didn’t get your extinct bird fix from my giant-penguin post, there’s plenty more news to go around. Greg Laden tipped me off to a gorgeous photo of the Recurve-billed Bushbird (Clytoctantes alixii), a bird that was once thought to have gone extinct. According to the National Geographic article, this bird was thought to have died out in 1965, but reappeared in 2004, although it has been seen seldom since. I’ll have to consult my copy of Errol Fuller’s Extinct Birds for more when I get home.

Perhaps even more momentous is the recovery of Dodo (Raphus cucullatus) remains from a cave on Mauritius, perhaps good enough to yield some DNA for study. The skeleton was in relatively good condition, although it doesn’t appear that it will be mounted or put on display (the only known soft tissue remains were saved from destruction in one of the most famous tales of academic heroism, and now reside in the Oxford University Museum of Natural History). Unfortunately Yahoo!News is not well-known for its excellent reporters, so details are scant at best. It’s definitely be something to keep an eye on, though.

Blogging Withdrawl

29 06 2007

For the next 9 days I’ll be petsitting and may or may not have access to the internet during that time, so whether or not I’ll be able to post anything new this weekend is anyone’s guess. You’ve got plenty to digest between giant penguins and deer sexual selection, and I know I usually don’t come up with anything that great on weekends, but I figured I would just let any readers know. It’s really funny how stat counters follow trends, especially in relation to ScienceBlogs (and especially Pharyngula). When SciBlings is having a slow day, I almost always have a slow day as well, and every weekend my stats do a bit of a nosedive only to resurface Monday, keep moving up through Thursday, only to taper off again. I’ve been getting many more visitors over the past few weeks so the counter shows less of a pattern, but previously my stat counter featured a few peaks and troughs of nearly the same amplitude and frequency.

Anyhow, yesterday Feduccia’s The Origin and Evolution of Birds, Romer’s Vertebrate Paleontology, and Quammen’s Song of the Dodo all arrived so I have no reason not to dig into at least one of them (more books probably coming today, and I’m about halfway through A Primate’s Memoir). So much to learn, so little time…


29 06 2007

I always get a little bit antsy when I see morning news reports about a new study appearing in Nature, Science, or some other journal, not having access to the actual paper until sometime later in the day. This past week, however, the mass-media slipped up a bit in this regard; they announced a new paper in the Proceedings of the National Academy of Sciences about two huge, extinct penguins on Tuesday, but the paper itself has only just now become available.

Giant Penguins
Art by Kristin Lamm. From right to left; Icadyptes salasi, Spheniscus humbolti (extant Humbolt Penguin), and Perudyptes devriesi

The reason this particular paper is so significant (other than 5-foot-tall penguins being utterly cool in and of itself) is that the prevailing hypothesis for penguin evolution was that they originated in cooler, southern latitudes and eventually made their way up to warmer areas like Peru, the Galapagos, etc. after temperatures during the Cenozoic began to cool. In fact, the Eocene (the time period in which the two new penguin species pictured above lived) experienced a temperature spike that threw various systems out of whack and contributed to the extinction of many groups of animals, including mammals. At the onset of the Eocene, there was a sharp thermal spike known as the Paleocene-Eocene Thermal Maximum, following by an overall rise in temperature before cooling down, and looking at the overall trend the world was much warmer during the time of the giant penguins than it is now, reversing the notion that penguins could only advance as far north towards the equator as cold temperatures would allow.

Analysis of the two penguins (there are also species yet to be identified from the same site, so expect more from Peru in the future) shows that they are not the ancestors of living penguins, belonging to the Order Sphenisciformes but outside the Family Spheniscidae, the authors citing the radiation that produced living groups taking places approximately eight million years ago during the Miocene. While much of the mass-media has focused on the “giant” size of Icadyptes, it should be noted that Icadyptes is only one of many known large, extinct penguin varieties, the largest yet known being Anthropornis nordenskjoeldi from Seymour Island and New Zealand, other examples being Pachydyptes ponderosus and Palaeeudyptes klekowskii.

Icadyptes is notable amongst its nearly equally-sized relatives for another reason; we wouldn’t expect to find such a large penguin in such a warm climate. While a foraminiferan indicative of warm-water has been found in association with the giant Pachydyptes, it was generally assumed that penguins followed “Bergmann’s Rule.” Bergmann’s Rule essentially states that among warm-blooded animals, we should expect body mass to increase with increasing latitude (hence, colder climates). This rule seems to work not only across species, but within species as well, working on the inherent plasticity of the animals to vary their size (i.e. wide-ranging animals are usually larger in the far north or south than close to the equator). Icadyptes gives “the flipper” to Bergmann’s Rule, being a warm-blooded bird in a hot environment of equal size to contemporaries from cooler latitudes, but there are exceptions to every rule.

The general reason why we observe Bergmann’s Rule is because of body heat; if you live in the cold you want to retain it, which large body size allows you to do, and in hot climates you don’t want to overheat, so it behooves you to be small and thus give off plenty of heat. Bob Bakker provides perhaps the best illustration of this in The Dinosaur Heresies; if you have to spend the night in a zoo and want to stay warm, should you snuggled up to one elephant (and remember, elephants are large and do live in hot climates, also “in violation” of the Bergmann’s Rule) or cover yourself with 100 bunny rabbits? The rabbits, although not even coming close to the mass of the elephant, radiate more heat, and while I think 100 is a bit excessive (I don’t want to toast in my sleep), you’ll be far warmer under their mass of fur than up against the wrinkly skin of an elephant. It is therefore apparent that something else is at work with Icadyptes; either there were patterns of upwelling that kept things cool enough for them (as in the case with Galapagos penguins today), or they were somehow otherwise adapted to keep their large body size without overheating in the equatorial region.

Overall, I am probably more excited about this find than I was about Gigantoraptor, and I actually enjoyed reading the PNAS paper (you need to be up on your anatomy to get the most out of the species descriptions, but otherwise it was easily accessible), and it seems to be a rare joy to find a paper that is both important and able to keep me engaged. I can’t wait to see what else has come out of the strata in Peru, and hopefully there can be a greater collaboration between paleoclimatologists, paleontologists, ecologists, and others to find out why there were giant penguins in the very last place we would expect to find them.

Deer Antlers; it’s not all about sex

29 06 2007

Female White-Tailed Deer (Odocoileus virginianus), taken in Hopewell, NJ

July 18th Update: LiveScience has caught onto the Nature paper and has a short article here.

A new Nature paper entitled “Sexually antagonistic genetic variation for fitness
in red deer
” (Foerster, et al., 2007) has some very interesting implications for fitness selection; the most fit males may not produce especially fit female offspring, and the most fit females may not produce especially fit male offspring. While it seems to be “common sense” that the most powerful, impressive male will father the strongest offspring, male and female Red Deer (Cervus elaphus) behave differently, and what makes a fit male does not make a fit female. The authors put it this way in their introduction;

Males compete intensely for matings during the short annual rut but do not invest in offspring care, whereas female maternal investment extends over a long period during each reproductive event. Consequently, male and female life histories are likely to be under divergent selective pressures, and a particular genotype may have very different effects on fitness in males than in females.

Males have to carry around a good deal of weight on their heads and be physically strong (thus the most “masculine” males being favored when it comes to breeding), while females have to raise the young all by themselves, better mothers leaving more offspring. This is not a revelation, but I have to admit that I never really considered the differing selective pressures between males and females in a population.

The primary trend pointed out in the paper is that females who mate with robust males typically produce daughters who do not leave as many offspring; we can’t simply say that the father has “good genes” offspring of both sexes will benefit equally from them. Likewise, it is not apparent if robust fathers leave especially productive sons; the deer are polyandrous, a few males mating with most of the females, and so many (if not most) of the males never successfully mate or leave any offspring.

An itchy Elk (Cervus canadensis) at New Jersey’s Turtle Back Zoo

Of further interest to us in this topic is another new paper by Jakob Bro-Jørgensen in the journal Evolution, “The Intensity of Sexual Selection Predicts Weapon Size In Male Bovids.” While Bovids are distinct from Cervids (deer) at the Family level, I think it’s important to compare the armaments of deer with those of bovids such as antelope, gazelle, buffalo, etc. The important distinction to make here (at least for our purposes) has to deal with the weapons the males conspicuously carry about; in deer, the males grow a new set of antlers every year, the antlers being made of bone and growing from an attachment to the skull called a pedicle. Horns, on the other hand, are typically hollow, have a covering of keratin, and do not fall off annually. All male deer have antlers, and many male bovids have horns, whether females have horns/antlers or not varying from species to species (i.e. female reindeer and caribou have antlers, but not as impressive at those of males. Even among species where antlers are not a typical female characteristic, some are commonly found to have antlers). All these details, of course, make generalization difficult, but there do seem to be some larger trends at work.

A Mhorr Gazelle (subspecies of Gazella damaAntler Size in Red Deer: Heritability and Selection but No Evolution” appeared in the journal Evolution, and the authors (Kruuk, et. al) found that directional selection for more impressive antlers is not happening because the success of the competing males depends on more than just antler size. Horns and antlers are dangerous things, and at least some weapon-wielding mammalian herbivores make at least some attempt at avoiding violent conflict. A male antelope that is obviously larger and has obviously bigger/longer horns than a rival will likely be able to drive off or otherwise force into submission a rival just because the rival knows he can’t possibly compete with such an impressive specimen, fights occurring more frequently when males are close to be equally matched (although things do not always proceed as orderly as this, some inadequate combatants giving it a go despite their less-impressive characteristics).

If a fight does occur, it’s not all about the antlers or horns; the weapons do not hold any sort of magic power that make their owner necessarily any more adept at fighting or stronger than any given opponent. Imagine, if you will, two men facing off with nearly equal length swords; how well they do while fighting does not so much depend on the blade but how they use it, strength, agility, health, and experience being more important than the weapon itself. Such appears to be the case with the antlers of red deer. While Kruuk’s study found that horns were heritable and did play an important role in sexual selection, how the competing males were doing in terms of health and nutrition mattered just as much (if not more) than antler size, a male will smaller/shorter/less impressive antlers able to beat a male with more robust antlers if he was physically stronger and it better health. Thus, nutrition and health mitigates runaway sexual selection for a dimorphic trait, essentially halting evolution. I especially liked the following quote from the conclusion;

Associations between phenotype and fitness, however appealing, will give a misleading impression of the potential for evolution in a trait if the true target of selection is unmeasured or immeasurable.

Indeed, sexual selection may have played the major role in the development of impressive antlers, but such evolution is not ongoing; there eventually comes a point where the antlers (and even horns or tusks) do not get bigger because the strength of competing individuals makes more of a difference than differences in antler size or shape. This study brought to mind the famous Irish Elk (Megaloceros giganteus), an extinct deer with perhaps the most impressive set of antlers known. There are hefty prices to pay when you have to not only carry such a huge rack about, but also to grow it. While their antlers were the size one would expect for their body size, they were still huge growths of bone, and these features may very well have contributed to its demise. While there does not appear to be any conclusive finding as yet, the size of the antlers may have prohibited the elk from moving through thick vegetation as climate and local ecology changed, or even suffered from various disorders/diseases as the nutrients in the soil needed to grow so much bone began to disappear. For now all we can do is look for more evidence to confirm or refute these hypotheses, but if either were true then natural selection would push against body form generated by sexual selection, showing us that we should be careful not to be become so enthralled with just one feature of an animal that we overlook all else.

If nothing else, the studies I’ve mentioned show us that there is certainly more to consider when it comes to sexual selection, reproduction, and evolution than the “most fit” males getting together with the “most fit” females and continuing the species; a more integrated approach is needed if we’re going to truly understand what’s going on and why the evolution of certain structures (especially those influenced by sexual selection) can come to a halt.


28 06 2007

Regarding “Lucy” going on tour, PZ writes the following;

Just a thought, but the creationists have got it all wrong. They think we worship Charles Darwin, but actually, if there are any objects of reverence among evolutionary biologists, it would be the evidence — the bones of Lucy, of Archaeopteryx, of Tiktaalik, the little trilobite in shale that I keep by my hand at my office desk.

Some days I swear that if I hear the word “Darwinism” or “Darwinist” one more time I’m going to scream; Charles Darwin was an exceptionally smart and unusual man, but I do not keep a little shrine next to my bed with a copy of On the Origin of Species that I read passages from every night before going to bed or anything of that sort. If there is anything that I truly have come to love and cherish in terms of evolution, it has been seeing the various forms of life that attest to it. The Berlin Archaeopteryx specimen is finer than any work of art, an Amur tiger roaring on a cold February morning more impressive than any poem… there is simply no way for me to look at the various life on earth, past and present, and think that they are not united by ancient ancestry and divided by processes that continually provide new reasons for excitement.

Even if certain fossils or organisms lose their privileged status as ancestors to other forms (and especially to us), they are no less amazing or beautiful. They are all complete in their own time, never quite finished in geologic time, “endless forms most beautiful” without question. I hate to make the religious analogy, but if I had my own place of worship it would be the fourth floor of the American Museum of Natural History. While many of the original fossils have been replaced with sturdy fiberglass replicas, a number of the real skeletons are still on display, the bones of creatures long-gone towering over the heads of all. Walking amongst the monstrous and terrible forms, I can’t help but sport a smile; I am among giants otherwise separated from me by a gulf of over 65 million years. Their bones correspond to my bones; we may have missed each other by a long shot, but we share a relative that provided us both with a wonderful body plan that has been carried through the rise and fall of many an evolutionary dynasty.

While it was remodeled in the mid-1990’s and will likely undergo future changes and renovations, I will never forget my first visit to the great Dinosaur Halls, awkwardly craning my head back to get a full view of animals that my imagination could not have conceived on its own. Without this love, this amazement when confronted so forcefully with what evolution has produced, I would make a rather poor scientist indeed. Writing papers in the passive voice, making tentative qualifications about hypotheses, and spending hours pouring through technical articles may be important to the academic advancement and standardization of science, but without the inner desire to discover more about nature, what good is all that? Without at least some amount of childlike enthusiasm, how can we ever hope to continue our enterprise or even interest others in it? While paleontology is the most famous discipline in which adults are supposedly paid to act like children, I think the sometimes near-inexhaustible inquisitiveness is an important part of what makes any good scientists; without it, it’s all just another job.

Just what is a Nimravid, anyway?

28 06 2007

Holophoneus Skull
Hoplophoneus sp. via Wikipedia

The saber-toothed cat is one of the most famous of prehistoric icons, but perhaps one of the most neglected when it comes to public understanding. While we know dinosaurs by their genus names (names like Tyrannosaurus, Apatosaurus, and Ankylosaurus are easily come to mind), few people are familiar with saber-toothed cat genera like Smilodon, Metailurus, Dinofelis, or Xenosmilus (and there are many more). What’s even more confusing is that what we often call a saber-toothed cat is not really a cat at all, but a related carnivore called a nimravid that was molded by a striking trend in parallel evolution.

Up until a few months ago, I have never even heard of the term “nimravid”, and I was quite surprised to find out that Barbourofelis and Hoplophoneus, two creatures I had always assumed were just another kind of saber-toothed cat, could not be called true cats at all. Skulls of these two genera (or manufactured facsimiles) usually sit in the same displays as those of Smilodon and other more-familiar saber-tooths, and I never thought twice to look for differences. How careless I was not to pay attention, and how careless of museums to keep lumping the remains of these separate lineages together with minimal comment.

Part of the problem with tracing the evolutionary history of mammalian carnivores is that they have generated an amazing amount of different forms; there is much diversity and plenty of branches, so every new fossil certainly can shake the tree. To keep things simple, however, all living carnivores evolved from a line of primitive carnivorous mammals called Miacids, with the Order Carnivora first becoming recognizable sometime during the Eocene (approx. 56-34 million years ago), the groups giving rise to modern dogs (Family Canidae) and cats (Family Felidae) diverging about 43 million years ago. Not all the groups that arose from the first true carnivores left living descendants, however, and such is the case with the nimravids.

Hoplophoneus mentalis via Wikipedia

So, what makes a nimravid a nimravid? They look awfully like cats, so why aren’t they lumped into the Family Felidae? What makes such distinctions so difficult is that those looking upon the skull of Smilodon and Eusmilus would have to be relatively well-versed in scientific jargon and anatomy in order to point out the most important differences. While some nimravids (like Eusmilus) had large canines, their teeth alone are not diagnostic, and the original factors used by E.D. Cope that differentiated these animals from “true” cats were the “alisphenoid canal, postglenoid foramen, carotid, posterior lacerate, and condyloid foramina, postparietal foramina” in the skull (Hunt, 1987). The various canals and foramina listed dictate the paths of various nerves and blood vessels in the skull, and the arrangement in nimravid skulls seem to be more primitive compared with true felids. Likewise, nimravids lack a two-chambered auditory bulla, which is a rounded bit of bone associated with the ear which true cats have (here’s a diagram of a dog skull pointing out the location of the bulla).

There are a few more obvious giveaways when dealing with some nimravids, however. Nimravids equipped with long canines often have more cone-shaped canines than saber-toothed cat canines (which are flatter in cross-section), and many have bony “sheaths” extending from the lower jaw into which the massive teeth fit. Perhaps the most famous example of this kind of arrangement is the genus Barbourofelis, an animal that has actually been assigned to its own family as it is likely more closely related to true cats than nimravids (Barbourofelis was previously classified as a nimravid). Because of this (and the fact that another cat-like offshoot, the marsupial Thylacosmilus) the tooth-sheath shouldn’t be considered diagnostic of nimravids only, but it does give you a substantial clue that you’re probably not dealing with an actual saber-toothed felid.

Skulls (mandibles not pictured) of 4 “saber-toothed” mammals from “The Function of Saber-Like Canines in Carnivorous Mammals” by G.G. Simpson, American Museum Novitiates, August 4, 1941. Pictured are A) Machairodus (felid), B) Hoplophoneus (nimravid), C) Smilodon (felid), and D) Thylacosmilus (marsupial).

You can see how complicated things can get; three different groups of animals arriving on the same body form from the same group of ancestors within a short amount of time. Indeed, saber-teeth seem to be a very common consequence for carnivores in this particular group, and oddly enough some living herbivores like the Musk Deer have impressive fangs as well. I’m not well-versed in evo-devo, but perhaps studying why musk deer develop such impressive teeth might give us some clues as to how it happened in these extinct cats, despite different ancestry. I should also perhaps mention that I’m curious about any sexual dimorphism between male and female saber-bearers; could sexual selection had a role in the extension of these massive canines? I don’t think it’s unreasonable to think so, especially if (as we’ll discuss) they were so long that they seemed to make these carnivores even more specialized in hunting, feeding, and social behavior than living carnivores.

Given the prevalence of massive canines amongst extinct felids and other groups, it’s a wonder why there are none living today (it should be noted, however, the Clouded Leopards have very long and impressive canines, even though they don’t peek out of their mouths when closed). It should also be noted that I have essentially left out a number of other, more distantly related saber-toothed carnivorous mammals called creodonts, which held saber-toothed hyenas like Hyaenodon in its ranks. For a time, it must have seemed like everyone and their mother had impressive fangs, and I can only wonder as to how these impressive structures became so-widespread.

It is not enough to merely say that nimravids are different, however; if they are not true saber-toothed felids, how closely are the groups related? Initially, some scientists thought that nimravids were ancestral to true cats based upon their more-primitive skull structure. As more fossils came out of the ground, the hypothesis that nimravids are closely related to true cats without being ancestral to them became favored, but this was overturned by the idea that nimravids and true cats are not very closely related, the nimravids diverging from the line that led to cats much earlier. This third view seems to make the most sense given the current fossil evidence, but I have to wonder how the reassignment of Barbourofelis will affect things, especially if it’s considered to be closer to felids than nimravids.

Here is a visual representation of the three hypotheses (which could be entitled “I can has MS Paint?”), after Hunt’s diagram in his 1987 paper;

Nimravid/Felid evolution

I included the “ancestral line” label in order to enforce the changing ideas about how evolution works, as well. In the first example the animals just kept evolving in the same line (they were the same genetic line, just with different species names as we came across them in the fossil record), but the third diagram shows that just because a new branch emerges does not mean that the ancestral line stops immediately. I have omitted Thylacosmilus and Barbourofelis as to keep things as simple as possible, and the fact that whatever I came up with would merely be a guess. I would also be remiss if I did not point this fact; while true saber-toothed cats do belong to the Family Felidae, they are all grouped together in the Subfamily Machairodontinae and do not have any living descendants. They diverged fairly early during felid evolution, ultimately becoming extinct, and I have hence tried to avoid the term “saber-toothed tiger” as much as possible. Because I’m trying to focus on nimravids for this entry I will keep the designation of “felids” for true saber-toothed cats, and hopefully I’ll eventually write a piece with more detail about the more well-known carnivores.

The big question involving these animals, however, is “How in the hell did they actually use those teeth?” Given that saber-toothed mammalian predators evolved three times in a geologically short time in three separate groups of predators suggests that they were useful for something, but how do you bite with teeth that extend past your lower jaw? In considering this question, it’s important to remember that when biting only the lower jaw is actually moving, so if a saber-toothed mammal wanted to impale a prey item with its long canines, it would have to throw its neck around with considerable force to achieve that end. In fact, this kind of action has already been proposed by some, the dynamics of felid saber-tooth skulls making it difficult to conceive how such huge canines could be used to effectively bite prey.

Part of the problem with having saber-teeth is that you need to open your jaw exceedingly wide in order to get food in your mouth. The oft-cited measurement for the gape of the felid Smilodon is 120 degrees (no source I’ve seen references where this measurement came from), and even if this is wrong we know that in order to get food into their mouths, many of the hyper-saber-toothed mammals would need to open their jaws to a 90 degree angle or more, otherwise they would not be able to get food in their mouths. What this means, as far as muscle strength is concerned, is that the muscles would not be as strong as in other cats, getting the mouth open being more important to a strong bite, so saber-toothed mammals would not have the crushing power of modern tigers or lions. Likewise, owning saber-teeth can make hunting difficult; if you stick your teeth into a live animal and it struggles, you could very well lose a tooth. Likewise the teeth would be more fragile, so putting extreme stresses on them (like crushing bone) would largely be out of the question too; it would be more effective and safe to attack soft parts of an animal than to try for the take-down neck-bites that modern cats employ.

We should be careful in our assumptions, however; we’re dealing with extinct animals, and their method of capturing/subduing prey may have differed significantly from any living carnivore. While I just mentioned that saber-toothed mammals likely had weak jaws, a 2005 study suggests that they had jaws as strong or stronger than living big cats, with different killing strategies depending on the overall durability/robustness of the saber-teeth. Likewise, an earlier study (1996) based upon tooth wear in Smilodon was unable to match wear indicative of bone crushing/chewing/abrasion with living hyenas, canids, and cats, suggesting that Smilodon may have avoided contact with bone as much as possible. Indeed, even though all these animals had impressive canines, not all their canines were equal, and some would be better suited to dealing with stresses involved with prey capture than others. Still, I would regard many of these teeth as delicate, and I can only imagine the pain these mammals must have endured when one of them broke.

Other hypotheses about how these animals employed their teeth involves the white shark-like tactic of disemboweling the softer underbelly of prey, then waiting for the eviscerated creature to die. This would be a rather risky move, the predator essentially sticking its head right between both sets of sharp hooves (assuming the prey was an ungulate). What seems more reasonable would be a strategy based upon cooperation, much like modern lions taking down huge water buffalo. If the group could bring down the prey with their claws, one animal could deliver the killing bite to the neck, minimizing the amount of potential harm to itself. This hypothesis, however, requires the study of behavior that we are no longer privy to, and it would be unreasonable to infer such a pattern on all saber-toothed mammals as the rule.

In his own paper studying the various methods of attack saber-toothed mammals could have used, G.G. Simpson concluded that they were best adapted for stabbing, not as much for slicing (although he conceded that they likely did this as well), the dentition of these animals showing their predatory habits (it had been hypothesized earlier that these animals may have been scavengers). Simpson’s study is interesting, but prey is generally not taken into account; only the effectiveness of different strategies for ripping up the assumed prey. While it certainly serves as a good reference point from a mechanical point of view, the skulls of the animals are considered out of context, and so the major mysteries of these animals remain unsolved.

Ultimately, all the known saber-toothed predators died out, regardless of their affinities. One of the most popular views (which I am surprised to still hear) is that the teeth of these animals simply became so huge that they could not properly open and close their mouths, driving the species to extinction. If there are urban legends in paleontology, surely this is one of the most annoying and persistent. G.G. Simpson refutes this idea in his popular work The Meaning of Evolution, published more than 30 years before I had heard it from various documentaries claiming scientific accuracy;

The sabertooth is one of the most famous of animals just because it is often innocently supposed to be an indisputable example of an inadaptive trend. In fields far remote from paleontology the poor sabertooth has some to figure as a horrible example, a pathetic case history of evolution gone wrong. Its supposed evidence is thus characteristically summarized in a book on (human) personality: “The long canine tooth of the saber-toothed tiger grew more and more into an impossible occlusion. Finally, it was so long that the tiger could not bite effectively, and the animal became extinct.” Now, like so many things that everyone seems to know, this is not true… Throughout their history the size of sabertooth canines varied considerably from one group to another but varied about a fairly constant average size, which is exactly what would be expected if the size were adaptive at all times and there were no secular trend in adaptive advantage but only local and temporary differences in its details. The biting mechanism in the last sabertooths was still perfectly effective, no less and probably no more so than in the Oligocene. To characterize a finally ineffective a mechanism that persisted without essential change in a group abundant and obviously highly successful for some 40,000,000 years seems quaintly illogical! In short, the “inadaptive trend” of the sabertooth is a mere fairy tale, or more fairly, it was an error based on too facile conclusion from imperfect information and it has since been perpetuated as a scientific legend.

Why saber-teeth seemed to be so trendy among predatory mammals, only to disappear entirely, I have no idea. Obviously they must have been good for something, some common developmental, ecological, or other trend driving canines to be longer, only to (perhaps) cause the animals to be so specialized that they could no longer compete with other carnivores who did not have to be so concerned about their teeth. At the very least, however, I hope this post have served to bring to attention a group generally overlooked, often mistaken for their cousins, when they have a rich evolutionary history of their own.


Hunt, R.M. 1987. “Evolution of the Aeluroid Camivora:Significance of Auditory Structure in the Nimravid Cat Dinictis“, American Museum Novitiates, Number 2886, pp. 1-74

Simpson, G.G. 1941. “The Function of Saber-Like Canines in Carnivorous Mammals“, American Museum Novitiates, Number 1130

Further Reading;

The Big Cats and their Fossil Relatives by Turner and Anton

The Velvet Claw by MacDonald

Evolving Eden by Turner and Anton

Fatalis by Rovin (fiction)

Wild Cats of the World by Sunquist

Excellent book: The Dechronization of Sam Magruder

28 06 2007

I’m not a huge sci-fi fan, but I have to say that G.G.Simpson’s novel The Dechronization of Sam Magruder is one of the most enjoyable works of fiction I’ve ever read. I’ll get to my take on who the narrator and Sam Magruder actually are and why this matters, but first I wanted to share this particular passage dealing with evolution;

It has been said by some theorists that cases like that of the crocodile, virtually unchanged for 100 million years and more, represent a failure of the evolutionary force, a blind alley, or a long senescence. As I gazed at my antagonist, it occurred to me how false this is. Here was no failure but an adaptation so successful, so perfect that once developed it has never needed to change. Is it, perhaps, not the success but the failure of adaptation that has forced evolving life onward to what we, at least, consider higher levels? The crocodile in his sluggish waters had perfectly mastered life in an unchanging environment. No challenge arose. Our ancestors lived in a more evanescent world, where what was adaptation at one time became an inadaptive burden in 100,000, 1,000,000, or 10 million years. For them, their adaptation was always a blind struggle to keep up, to face new conditions, to exploit new opportunities. Only changing races met that challenge. Of the others, those to whom chance close the adaptive avenue of change, the unlucky became extinct and the lucky, like the crocodile, found and settled into some way of life where the challenge was absent, and there they stagnated.

Indeed, crocodiles are fortunate; adaptation and evolution has perfected them to exist in a niche that does not require major changes provided that conditions don’t drastically change overnight. Even before there were actual crocodiles, there were tetrapods essentially filling the same niche of aquatic ambush predator, and for one reason or another crocodiles beat them all out, so well-adapted to their role in the ecosystem that there hasn’t been much need for big-time evolutionary change. If there was anything like a communal memory of crocodiles, there wouldn’t be a memory of a time when there was not water to conceal themselves in, and they have been preying upon the various creatures that have visited the water’s edge the whole time. While there was once a greater diversity of crocodiles in type and habit, they have dominated their niche for so long that there is seemingly nothing they cannot handle.

This passage also speaks to what wrote in popular works like The Meaning of Evolution, in which he refutes the idea that life has some sort of vital force pushing it forward to be constantly evolving (or the idea that species, like individuals, had lifespans of birth, growth, and “senescence”), nor does evolution strive toward one perfect, unchangeable end (although crocodiles probably fooled many in this regard). While crocodiles will continue to change little by little through time, I can’t think of a reason why they should not continue to persist much as they are now for many millions of years to come.

As for the book itself, I feel that our protagonist Sam Magruder and the narrator are dual-voices of G.G. Simpson. Magruder, a scientist who is utterly lonely and stuck in a world where he feels he cannot make any lasting contribution to science, is the most powerful voice in the story, but I feel the narrator tells us quite about Simpson as well. Magruder’s story is told via 8 stone tablets that Magruder inscribed and buried, but not all the content of the slabs is shared with the reader; the academics who are disseminating the information have edited it, inserting lengthy footnotes, snide remarks, and editing what they deem to be distasteful. One such example is Magruder’s discussion of his sexual frustration, no female of his species existing for more than 65 million years into the future, but the editors decide this discussion is too frank and omit it from the public’s copy. Likewise, the narrator makes mention of, but omits, various footnotes of academics apologizing for Magruder’s behavior (such as using a colloquialism, which is apparently unbecoming of a scientist) and his ignorance of a topic (such as when sauropods became extinct in North America). These were Simpson’s little jabs at academia, perhaps venting his own frustration at fellow scientists who lacked imagination or developed a “holier-than-thou” attitude over the years.

While I did not know this about Simpson, the afterword by Stephen Jay Gould makes it clear that Simpson was a very lonely man despite his accomplishment. This was not for lack of company, but Simpson wanted so much to contribute something lasting to paleontology that he could seemingly could not bear much criticism or brown-nosing (which was worse), and the book makes it apparent that he was worried he would be forgotten. While Magruder buried his slabs, never knowing whether someone would find them (he’d be dead for at least 65 million years when they did), Simpson seemingly buried this bit of fiction, which did not come to light after his death. At the end of his life, perhaps Simpson felt like Magruder; contributing much to our understanding, but isolated from anyone who would study his work in the years to come, isolated from satisfaction and afraid that his work would be left to collect dust on a shelf somewhere. What gratification he might have gotten from people like me who are still impressed by his work, I don’t know, but it seems that intellectually Simpson felt he was stuck in the Cretaceous, never knowing what would become of the messages he left to future generations.

If you enjoy science fiction at all, and especially if you like tales about dinosaurs, I highly recommend this book; it can be read cover-to-cover in less than an evening and gives us a very personal look at one of the greatest paleontologists ever to have lived. Immediately after I closed Simpson’s book, I picked up Sapolsky’s A Primate’s Memoir, and it only furthered my enjoyment for the evening. I have absolutely loved the first 60 pages of Sapolsky’s book, and I can’t wait to get to the rest of it; it is another must-read if you’re looking for good books this summer.

In the field with Barnum Brown

28 06 2007

Lilian MacLaughlin Brown’s Bring ’em Back Petrified was an interesting read as it provided a look at one of the world’s greatest fossil hunters looking for his quarry in one of the hardest locales to tackle; the jungle. While Barnum’s wife doesn’t seem nearly as interested in fossils as being a sort of housewife in the field, she does prove some interesting (if short) accounts of work in the field.

He hitched up his pants, spat on his hands, stepped forward and brought his pick down like a sledge hammer, shattering the limestone rock. He picked up a fragment. Out of his pocket came the hand lens, and, training it on the specimen, he squinted down into the glass. Rufio and Lolo stood a few paces behind, exchanging looks and whispers. There are times when Barnum is as finicky about noise as a golf champion on the green. This was one of them. Now an irritate cough hinted that his concentration was being disturbed by the men’s whisphering. They took the hint. We all stood like statuary – waiting.

At last he came to life with a, “hmmmmmm,” which I recognized as a good sign – particularly when he followed this by pulling out his pipe and tobacco pouch. Barnum always pulls out his pipe when he prepares to develop a dig. It’s an English briar, a smelly thing he latched onto sometime before we were married, and so heavy he has to rest his jaws between puffs. Why he keeps it is a mystery, although it does make him look a little like Sherlock Holmes.

I had to nudge him with a questioning, “Yes-s-s?” before bringing him entirely out of his trance. Even then he filled and lit his pipe before favoring me with a smiling,
“It’s our sea-bed alright, Pixie.”
Picking up another rock fragment, he examined it through the lens, then suddenly emitted a jubilant,
“FORAMINIFERA! Stand back, everyone. Nobody touch the rock. We’ve got foraminifera!”
Lolo threw Rufio a look of alarm. “Is this bad? Are we get a sickness?”
“No,” said Rufio, “I think it is something scientific. And many times,” he added, in a whisper, “that not so good either.”

Both turned to me for enlightenment but I could only shake my head and nod towards Barnum. No scientist is in an explanatory mood when he has just made a discovery. Having prospected the rocks for his information, he himself must be prospected if one is to pry that information loose. Only one doesn’t do it with his pick. One wheedles-particularly at night when a scientist’s defenses are down. Since this was daytime, I decided on the direct approach. Barnum was hunkered down working his pick point carefully over the rock.
“what,” I asked, giving the question a casual twist, “is foarminifera?”

The pick halted in mid-air. His head and neck took on a peculiar rigidity. Turning slowly, he eyed me in such a “violent” manner that Rufio stepped gallantly forward to my defense.
“Señor, we only like to know-”
“You stay out of it, Rufio,” Barnum barked. “This is a family affair.”

Although I soon caught the melodramatic undertone, for an instant indignation welled up in me.
“Can’t a person even…?” I began.
It was Barnum’s clue to clap a hand to his forehead, actor-like, and go on with the melodrama:

“That a woman of mine should ask what a foraminifera is!” he orated. “A woman who was with me when I dug up the Colossochelys atlas in India; who watched me unearth the Samotherium and Sivatherium; who helped me with my Wyoming sauropods; who…” He broke off his act, and laughed at the blank look on the men’s faces.

I laughed. The men laughed. The Señor Doctor was loosening up.