What big teeth you have…

3 10 2007

Smildon

One of Charles R. Knight’s paintings of Smilodon fatalis, this one menacing a giant sloth stuck in tar (off panel).

There are few fossil mammals that are as impressive the saber-toothed cat Smilodon fatalis, but despite it’s fearsome dentition some recent new reports have suggested it was more of a pussycat when it came to bite strength. This seems to be counter-intuitive; how could such an impressive animal be associated with the term “weak”? Part of it has to do with word choice, but the larger issue has to do with the fact that the bite of Smilodon wasn’t as strong as that of some other carnivores (extinct and extant), as well as dentition and feeding ecology. This issue goes far beyond just one genus or species, however, as Smilodon was only one of many genera that bore massive canines. In fact, huge “sabers” have evolved over-and-over again in the mammalian lineage (see this post and also this post for information about the cat-like ones), including the famous fangs of the machairodontine felids (saber-toothed cats) and their look-alike nimravid relatives.

Tusks

Lateral, anterior, and dorsal views of the herbivore Uintatherium (Note the prominent canines). From Marsh, O.C. “The Fossil Mammals of the Order Dinocerata.” The American Naturalist, Vol. 7, No. 3. (Mar., 1873), pp. 146-153

Cope

Skull of another member of the Dinocerata; “Loxolophodon cornutus” (today known as Eobasileus cornutus). Again, note the prominent canine. From Cope, E.D. “The Amblypoda (Continued).” The American Naturalist, Vol. 19, No. 1. (Jan., 1885), pp. 40-55.

Although this post will primarily be concerned with the great “sabercats,” large, dagger-like canine teeth having been evolved multiple times by many different unrelated animals during the course of life on earth. In some herbivorous creatures, like the extinct Uintatherium and even in the extant Musk Deer, the fangs reflect sexual dimorphism and probably sexual selection, but the sharp teeth don’t seem to have a prominent function in mastication or processing of food. Likewise, large canine teeth are present in living baboons (Papio sp.), and the sexual dimorphism exhibited between the dental equipment of the males and the smaller canines of the females has long been noted (males often yawn to show off their canines, the size of their teeth being very intimidating indeed). Do the same considerations of sexual selection and dimorphism hold true for the saber-toothed cats, too? Unfortunately, fossil evidence does not always allow comparisons of the two sexes, but extant big cats and some death-trap sites have provided some information to work with. From Salesa, et al. (2006);

Among the Carnivora, sexual dimorphism is more marked in canine size than in other dental features or skull size, and these differences can be related to the breeding system. Species in which a male defends a group of females tend to be more dimorphic than those with monogamous pairs or groups of males and females. Felids are dimorphic animals, but mainly in reference to body size, with the mane of male lions being a unique example of morphological variation between sexes among the family.

This makes sense; if a male keeps a harem of females and has to defend it from other males, the species is more likely to exhibit sexual dimorphism than not. In cats, however, it seems to be more about body size (and possibly characters that wouldn’t fossilize in extinct species) than about tooth size (which would serve important other functions, so any sexual selection would be mitigated by natural selection), although we can’t be sure of this being that there are no living sabercats to study. Personally, I think there could be a sexual-selection component in some groups, but the saber-canine is so prominent in so many extinct felids and nimravids that it is extremely doubtful that all the lineages converged on similar tooth structures because of sexual selection/dimorphism, the functional advantage of larger teeth likely coming first. A lack of sexual dimorphism when considering morphology as a whole, however, may suggest a more solitary lifestyle where territories may or may not overlap are maintained and direct competition for females is not as fierce, especially since the females move through territories rather than living with a male. Such a strategy may have been employed by the late Micoene sabercat Paramachairodus ogygia. Salesa, et al. (2006), working with an assemblage made up of many of the more basal felids, have even been able to come up with a hypothesis about life history of the ancient animals based upon their finds in Spain;

[T]he probable territorial behaviour for Par. ogygia would be very similar to that of jaguars, in which males defend large, overlapping territories that include smaller territories of several females. This model is similar to that of the leopard, but in this species male territories never overlap, which could explain the different sexual dimorphism index of this species with respect to Par. ogygia and jaguar…

So, if Par. ogygia behaved more like jaguars and leopards than lions, the presence of juveniles in the trap would be highly improbable, as is the case. But in addition to the scarcity of juveniles, the sample from Batallones-1 has another interesting feature: it is mostly composed of young adults, that is, individuals with the complete permanent dentition, but without any trace of wear. These animals, which would have recently become independent of their mothers, would not as yet have had any territory, moving instead through the ranges of other adults and being more easily attracted by an easy meal, such as carrion. This age distribution therefore suggests that the sample of Par. ogygia trapped in Batallones-1 corresponds to that fraction of non-resident young individuals, both males and females, which were in a phase of dispersion. In the case of leopards, such individuals are more daring – or less cautious – than adults, and they have been seen crossing rivers in spate, whereas resident adults only cross at times of lower water. It has also been noticed that among these individuals, males are even more inclined to make these incursions than females, which remain longer with the mother, especially if there is good availability of food. If this pattern of dispersion behaviour applied to the young adults of Par. ogygia, it is likely that they were trapped in Batallones-1 more often than the resident adults.

Saber Tooth Diversity

Saber-Toothed Felid and Nimravid diversity (click for a larger image). From Emerson, S.B., and Radinsky, L. “Functional Analysis of Sabertooth Cranial Morphology.” Paleobiology, Vol. 6, No. 3. (Summer, 1980), pp. 295-312.

While the life histories of extinct mammalian carnivores are interesting in and of themselves, it is the teeth and terrifying bite of the sabercats that we are most concerned with here. Smilodon is the celebrity of saber-toothed cats, but the fossil record preserves a wide diversity of carnivores with large canine teeth, and even within the larger groupings there are even more subdivisions, the skulls of saber-toothed felids being widely variable. As discussed in the background material, nimravids are saber-tooth look-alikes that diverged from a common ancestral line earlier than the carnivores that would give rise to Smilodon, but the two lines are still closely related and have undergone parallel evolution. There is still some reshuffling of taxa going on and the true evolutionary history/affinities of many of the forms is still being worked out, but most forms you’re likely to see grouped together at a museum fall into either the nimravid or felid camps. The focus of this essay, however, will be on felids, and although they are often discussed along with their nimravid cousins the larger amount of work has been done on the felids and so we must leave the nimravids.

With the felids, then, there seem to be three kinds of sabercat that hint at differing predatory tactics, prey, and habitat. Indeed, evolution did not create carbon copies of the same creature, barring life from becoming adapted to varying circumstances; there is more variety than would be first assumed if we based all our research on the presence of prominent canines. Instead, there seem to be three “ways of being” a saber-toothed cat, as outlined by Martin, et al.;

Saber-toothed carnivores… have been divided into two groups: scimitar-toothed cats with shorter, coarsely serrated canines coupled with long legs for fast running, and dirk-toothed cats with more elongate, finely serrated canines coupled to short legs built for power rather than speed. In the Pleistocene of North America, as in Europe, the scimitar-cat was Homotherium; the North American dirk-tooth was Smilodon. We now describe a new sabercat from the Early Pleistocene of Florida [Xenosmilus], combining the scimitar-tooth canine with the short, massive limbs of a dirk-tooth predator. This presents a third way to construct a saber-toothed carnivore.

Three Kinds

Xenosmilus hodsonae, Homotherium cf. crenatidens, and Homotherium serum. From Martin, L.D., Babiarz, J.P., Naples, V.L., and Hearst, J. “Three Ways To Be a Saber-Toothed Cat.” Naturwissenschaften, Vol. 87, No. 1 (Jan. 2000), pp. 41-44

As Martin notes, there appears to be a number of adaptational “trade offs” that sabercats in North America and Europe were subject to; fast-moving gracile forms had shorter sabers, but stouter and more powerful forms had the longer, more laterally flattened canine teeth. The “third way” that combined characters from both groups was exemplified by Xenosmilus (which Martin, et al. say would have seemed more like a bear than a cat, despite actual evolutionary relationships to the contrary). Still, leaving the overall structure of the body aside for a moment, the arrangement and sizing of the teeth of the different groups can be very telling. Martin, et al. again lay out what the usefulness of the differing tooth arrangements;

When biting, the long sabers of dirk-toothed cats may have cut parallel slits for some distance before the relatively smaller incisors could be applied. In scimitar-toothed cats the shorter canines and longer incisors worked more as a unit, first cutting parallel slits with the canines, immediately followed by the incisor arc removing the strip of flesh. Such a large open wound would have bled profusely, traumatizing the victim. If the incisors and canines acted in unison, the torsional forces on individual teeth would have been reduced, resulting in fewer restrictions on bite placement. In felids the size of the sagittal crest is directly proportional to the forces exerted by the temporalis musculature. Scimitar-toothed cats have a sagittal crest that is generally less pronounced than that in their dirk-toothed contemporaries. In a modification of the typical scimitar-tooth condition, the new cat from Florida exhibits both an elongated sagittal crest and an enlarged temporalis muscle that would have permitted a stronger bite.

While such a passage might not seem significant at first, it shows that there is more going on in a sabercat’s skull that is important to biting than just the size or shape of the canines. The placement of the incisors, for instance, seem to make a difference in biting strategy and force, dirk-toothed cats like Smilodon exhibiting a condition where the incisors are out forward of the canines. When this is taken into account, as well as the length of the canines, it seems that the canines would slash for quite some distance before the incisors could be used at all in comparison to the scimitar-toothed sabercats, the placement of the incisors in scimitar-tooths seemingly strengthening the biting teeth at the front of the jaw. The sagittal crests of these creatures should also be taken into account, such structures giving students of paleontology an indication of how carnivores (or herbivores, in the case of gorillas) have been adapted to achieve higher bite forces. Such ridges atop the skull for muscle attachment are not unique to sabercats, however, and there are some animals that have taken the structure to even greater extremes;

Amphicyon

The extinct “bear dog” Amphicyon at the AMNH. Note the size of the sagittal crest, the reduction of the bony enclosure around the eyes, and the large holes on the side of the skull for jaw muscle attachment.

Hyaenodon

The extinct “saber-toothed” creodont Hyaenodon at the AMNH. Again, note the sagittal crest, reduction of bone enclosure around the eye, and the large canines.

Hoplophoneus

The skull of the nimravid Hoplophoneus on display at the AMNH. Note the size of the canines and sagittal crest in comparison with Hyaenodon and Amphicyon.

Smilodon

The skull of Smilodon on display at the AMNH.

Thylacoleo

The skull of the marsupial predator Thylacoleo at the AMNH. Note the large openings on either side of the skull for the jaw muscles.

Thylacoleo

Ventral view of the skull of Thylacoleo. From E.D. Cope’s “The Tertiary Marsupialia” in The American Naturalist, Vol. 18, No. 7. (Jul., 1884), pp. 686-697.

Looking at the various groups, all show adaptations that increase the amount of available muscle attachment to achieve more powerful bites, modifying the skull in two ways. First, a sagittal crest (as already discussed) is often present to some degree, often being greater in omnivores or bone-crushing carnivores as they require greater forces to crack hard foods (although recent research by Wroe, et al. suggest that bone crushers like Spotted Hyena might not have the highest bite forces). Likewise, the holes between the skull and cheek bones are often enlarged or widened (the extreme of this group being Thylacoleo), the more muscle that can pass from lower jaw to skull being directly correlated to bite strength. What is interesting about sabercats, when considering these factors, is that they seem to be in the middle. They don’t exhibit adaptations of the skull to the extreme as in Amphicyon or Thylacoleo, but they still exhibit changes allowing for powerful bites (strong enough to kill and consume prey, at least). The trend is obvious and has not been missed by reseachers, and Emerson says the following about it;

With enlargement of upper canines, skulls of paleofelid, neofelid, marsupial and, as far as the record shows, creodont sabertooths were remodeled in similar ways. This evolutionary convergence in cranial morphology is not surprising, since most of the modifications relate to allowing increased gape while retaining bite strength at the carnassial. Those are factors essential for all sabertooths, and the possible ways to achieve them, starting from a generalized mammalian cranial morphology, are limited…

Why did sabertooth specializations evolve so many times? Their multiple evolution, plus the fact that several species of sabertoothed felids existed for most of the history of the family (from about 35 Myr to about 15,000 yr BP) suggest that sabertooth canines provided an effective alternative to the modern carnivore mode of killing prey

Megantereon

The skull of the saber-toothed cat Megantereon. Like in Smilodon, not how the incisors jut out (as well as the overly large nasal opening in this genus).

The basic mechanics of the skull just discussed gives researchers clues as to how sabercats could have killed their prey, but reconstructing ancient predator/prey interactions with no exact modern equivalent is difficult. Indeed, debate has gone on for years as to how sabercats used their teeth to bring down prey (see Simpson’s paper), either by stabbing, cutting, slicing, or even (as silly as it may seem) by crushing. What does seem apparent today, however, is that the canines of the sabercats were relatively delicate, and it would be unwise to fully sink them into a struggling animal as they may easily be broken off. Even if such an attempt to deeply puncture a prey item was not undertaken, biting full-force into bone could have also easily damaged teeth (or even broken them off), making it unlikely that sabercats jumped onto the back of their prey and tried to sink their teeth into the back of the prey’s skull like some modern cats. Recent research has even shown that the skull of Smilodon was ill-suited to handle stresses associated with struggling prey when compared to the skull of a lion, and I wonder how often individual Smilodon perished because of stresses associated with taking down prey if the victim was not brought down and killed quickly. Indeed, it seems that the long teeth were better suited to slicing soft flesh, i.e. cutting open the belly of prey or slicing open the throat, rather than piercing rough hides and ramming through bone.

Saber Tooth

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).

As just discussed in terms of tooth and skull stressed, many factors of life history, behavior, and morphology of extant big cats and sabercats might be similar, but the massive canines of the extinct group seem to infer a different killing strategy, and there is no reason to assume that they were like modern big cats in every respect. Salesa, et al. sums it up this way;

Extant felids kill small animals by biting on the nape or directly on the skull, using their rounded-section canines, but if any sabre-toothed cat tried to do this they would have risked breaking the laterally flattened upper canines. For this reason, it is more probable that they developed some behavioural mechanism to minimize that risk, such as ignoring prey below a given size. It is likely that machairodontines developed this ethological trait early in their evolution, and so narrowed their prey size range in comparison with that of felines, which hunt both large and small animals. This high specialization has been pointed out as one of the possible reasons for the gradual decline and final extinction of the sabre-toothed cats in the Pleistocene… The development of this strategy was probably the key reason for the sabre-tooted cats becoming the dominant predators in the land mammal faunas from the Late Miocene to Late Pleistocene.

It might not immediately make sense that felids with fragile teeth would specialize in eating large prey, but that is whale the fossil evidence (as we currently understand it) infers. While the smallest prey would pose no problems (outside of not being a fully satisfying meal), but medium sized prey with smaller areas of soft flesh (like the stomach and neck) would potentially be more dangerous and a more exact bite would be needed to prevent damage to the teeth and skull. Hence, it seems that the slashing and ripping of soft tissue in larger animals was the main method of killing prey (after it had been brought down or slowed by blood loss), taking hypercarnivory to an even more specialized extent.

Amur Leopard

An Amur Leopard yawns. Note the relatively small (but still fearsome) canines of the upper and lower jaw.

What, then, of a smaller living cat, the Clouded Leopard (Neofelis nebulosa and N. diardii), which has been heralded as a modern analog of sabercats? As Christiansen notes, Clouded Leopards are a bit bizarre, and it is incorrect to call them “small” big cats or modern sabercats, the genus showing a number of convergences with extinct forms while remaining distinct from the famed genus Panthera;

The skull morphology of the clouded leopard sets it apart from other extant felids, and in a number of respects it approaches the morphology of primitive sabertooths. This indicates convergence of several characters in machairodontine felids and the clouded leopard, mainly as adaptations for attaining a large gape. This raises doubts about the characters hitherto considered as distinguishing sabertoothed from nonsabertoothed predators…

Clearly, Neofelis and the sabertooths independently evolved a suite of the same specializations for the same overall purpose of attaining a large gape, a prerequisite for efficient jaw mechanics with large canines, but the reasons for evolving these characters need not have been similar. Based on analyses of lower jaw bending moments and inferred resistance to mechanical loadings, Therrien (2005) suggested that Neofelis could be at the beginning of a new sabertooth radiation. Such claims are difficult to test, however, since the extant sister taxon to Neofelis (Panthera) shares none of its sabertoothed characters, and the fossil record provides no clues of felids closer to Neofelis than Panthera. At present, however, there is little evidence to suggest that Neofelis can be regarded as an “extant sabertooth,” although it clearly shares a number of characters with them that are absent in other extant felids. On the other hand, it cannot be regarded as simply an intermediate between large and small felids, as normally assumed. The presence to some extent of characters normally ascribed to sabertooths in Neofelis raises doubts about their functional and evolutionary significance in primitive machairodonts such as Nimravides or Paramachairodus, hitherto the only reasonably well-known primitive machairodont. Such animals need not have shared the presumed functional skull morphology of later, more derived sabertooths and are perhaps not to be regarded as “sabertoothed” at all, if by sabertoothed is implied animals functionally significantly different from extant felids.

Again, this shows a convergence of functional morphology despite existing evolutionary relationships, many felids being adapted in similar ways. As stated previously, the large canines of saber-toothed predators required the animals to open their jaws wide but also narrowed their predatory niche to some extent. Likewise, various tests seem to show that the bite of sabercats like Smilodon was “weak,” with news reports often relating that the terrible felids were more like big housecats when compared to living big cats. This is a mistake (and it would be a grave one for anyone ever to cross a sabercat), born of a lack of recognition that bite forces exist on a continuum and are related to a number of factors and cannot simply be deemed “weak” or “strong” without further comment. Christiansen relates the bite force of Smilodon as such;

[A]lthough large sabertooths such as Smilodon and Homotherium had weaker bite forces than lions or tigers, their bite forces were broadly comparable to those of jaguars and large leopards, and, thus, cannot be claimed to have been “weak”. Lower bite forces at any given body size were probably evolutionarily possible owing to a marked contribution from the upper cervical musculature to the killing bite, which… was absent in Neofelis and primitive machairodonts such as Paramachairodus. Thus, bite force analysis may constitute a hitherto overlooked parameter in evaluating whether or not primitive machairodonts such as Paramachairodus or Nimravides really did employ a canine shear bite with a marked contribution from the cervical muscles to subdue prey, or killed in a manner similar to extant felids, which requires a stronger killing bite…

In many Plio-Pleistocene communities predator competition was more severe than today, and a sabertooth killing mode could be a way of ensuring faster kill rates, since a throat shear-bite most likely would kill prey faster than a throttling throat bite, common in extant pantherines. In lions, it can take up to 13 minutes to kill large prey, and in such cases the prey is frequently killed by disemboweling by other pride members. In the cheetah a suffocation bite can take even longer to kill prey. Carcass theft and feeding competition is very common among extant large, sympatric predators, and a faster kill mode could be a way of reducing the risk of carcass theft from competing predators. In many large predators with sympatric competitors, rapid consumption can be a way of reducing the risk of carcass theft, and this would most likely have been accentuated in past ecosystems with more intense large predator competition. Accordingly, the morphology and behavior of extant predators need not reflect the circumstances to which they became adapted when they evolved. More intense competition could accelerate the evolution of a sabertooth morphology…

This passage reflects the problems with reconstructing bite forces and predation techniques of extinct creatures; more is involved than just the opening and closing of the jaw. The neck muscles of many sabercats (except in some of the more basal members, as noted) likely contributed to the strength of the bite in a way that’s not directly testable today. Likewise, the killing technique of sabercats might not have required a bite as strong as a modern-day tiger, as in a land filled with other predators, it might simply take too long to try and suffocate a prey animal or bite through the back of their skull. Disemboweling or tearing out the throat of the prey item, by contrast, is a much quicker way to do large amounts of damage but it seems that it would require teamwork, solitary extant big cats often opting for a killing neck bite when the prey has been brought down. Even if this is eventually shown to be incorrect, it should be remembered that bite strength is not everything; despite its large size, the Great White Shark (Carcharadon carcharias) has a relatively weak bite, but it makes up for it with heavily serrated teeth, force of impact when attacking prey, and side-to-side head shaking to saw through its food. Crocodilians, by contrast, have very strong bite forces but they don’t saw through prey or chew, the emphasis being holding on to struggling prey and drowning it before ripping it apart. Such considerations bring us to another point mentioned above in our discussion of scimitar-tooths vs. dirk tooths in that the famous dirk-toothed cats like Smilodon were more powerfully built, seemingly focusing on bringing a large animal down to the ground and then delivering devastating bites once the stomach and neck were exposed (a process that would be made easier by groups working together, as seen in modern examples like lions bringing down giraffes or elephants).

A group of lions brings down a giraffe.

A group of lions brings down an elephant.

A new paper, just out in PNAS, does take the powerful neck muscles of Smilodon into account, however, and the information from the new models appear to corraborate the modern understanding of a felid that captured and killed prey in a way quite different from Panthera. From McHenry, et al.;

Our results demonstrate that bite force driven by jaw muscles was relatively weak in S. fatalis, one-third that of a lion (Panthera leo) of comparable size, and its skull was poorly optimized to resist the extrinsic loadings generated by struggling prey. Its skull is better optimized for bites on restrained prey where the bite is augmented by force from the cervical musculature. We conclude that prey were brought to ground and restrained before a killing bite, driven in large part by powerful cervical musculature. Because large prey is easier to restrain if its head is secured, the killing bite was most likely directed to the neck. We suggest that the more powerful jaw muscles of P. leo may be required for extended, asphyxiating bites and that the relatively low bite forces in S. fatalis might reflect its ability to kill large prey more quickly, avoiding the need for prolonged bites.

Hunting isn’t the only aspect of sabercat predation that seems to have differed from modern carnivores; they way they ate (and what they ate) is somewhat at variance with modern forms, as well. As is apparent at this point, the contact of the canines with bones would have been avoided, and it seems that the hard parts of the skeleton would have been avoided when a sabercat was consuming it. This could differ among different groups (perhaps some of the shorter-toothed forms not being so finicky about bone), but research into microwear patterns on teeth of Smilodon don’t seem to match with wear patterns of any living carnivores, suggesting a different dietary preference. It could be hypothesized, then, that creatures like Smilodon primarily consumed the soft parts of the carcass or what could be removed without too much damage to the teeth, and it should be remembered that living big cats often do not eat every part of the skeleton. Some, like cougars, have favored parts that they eat but end up leaving as much as 40% of the carcass behind. Other predators, especially bone-crushing ones, could take advantage of the leftovers, although the felids might have had to eat quickly as some of their osteophagus competitors may not have been patient (and, in fact, lions and hyenas often fight over kills and steal them from each other today).

Given all the prior considerations, it now seems that sabercats specialized in bringing down relatively large prey down quickly (some likely working in groups to do so), killing the victims by slashing open their stomachs or slicing through the blood vessels of the neck. This would be a much messier, but quicker, method than employed by living big cats, although the limitation of food sources likely caused in the eventual downfall of sabercats. Hypercarnivory can be a dangerous adaptive path to go down, and cats are clearly the most meat-dependant of the Carnivora, but it seems that extinct forms took their dental and dietary specialization above and beyond what is seen today. The price paid for such adaptations ended up being extinction, but given how many times they have shown up in the history of life on this planet, someday there may again be a saber-toothed predator stalking the shadows.

References;

Anyonge, W. “Microwear on Canines and Killing Behavior in Large Carnivores: Saber Function in Smilodon fatalisJournal of Mammalogy, Vol. 77, No. 4 (Nov., 1996), pp. 1059-1067

Christiansen, P. “Canine morphology in the larger Felidae: implications for feeding ecology.” Biological Journal of the Linnean Society. Vol. 91, No. 4 (Aug., 2007), pp. 573-592

Christiansen, P. “Sabertooth characters in the clouded leopard (Neofelis nebulosa Griffiths 1821).” Journal of Morphology, Vol. 267, No. 10 (Jul., 2006), pp. 1186 – 1198

Christiansen, P. and Wroe, S. “Bite Forces and Evolutionary Adaptations to Feeding Ecology in Carnivores.” Ecology, Vol. 88, No. 2 (Feb., 2007), pp. 347–358

Cope, E.D. “The Amblypoda (Continued).” The American Naturalist, Vol. 19, No. 1. (Jan., 1885), pp. 40-55.

Cope, E.D. “The Tertiary Marsupialia.” The American Naturalist, Vol. 18, No. 7. (Jul., 1884), pp. 686-697.

Emerson, S.B., and Radinsky, L. “Functional Analysis of Sabertooth Cranial Morphology.” Paleobiology, Vol. 6, No. 3. (Summer, 1980), pp. 295-312.

Leutenegger, W., and Kelly, J.T. “Relationship of sexual dimorphism in canine size and body size to social, behavioral, and ecological correlates in anthropoid primates.” Primates, Vol. 18, No. 1 (Jan., 1977), pp. 117-136

Lucas, P.W., Corlett, R.T., and Luke, D.A. “Sexual dimorphism of tooth size in anthropoids.” Human Evolution Vol. 1, No. 1 (Feb., 1986), pp. 23-39

Marsh, O.C. “The Fossil Mammals of the Order Dinocerata.” The American Naturalist, Vol. 7, No. 3. (Mar., 1873), pp. 146-153

Martin, L.D., Babiarz, J.P., Naples, V.L., and Hearst, J. “Three Ways To Be a Saber-Toothed Cat.” Naturwissenschaften, Vol. 87, No. 1 (Jan. 2000), pp. 41-44

McHenry, C.R., et al. “Supermodeled sabercat, predatory behavior in Smilodon fatalis revealed by high-resolution 3D computer simulation.” PNAS, Published online before print October 2, 2007

Salesa, M.J., et al. “Aspects of the functional morphology in the cranial and cervical skeleton of the sabre-toothed cat Paramachairodus ogygia (Kaup, 1832) (Felidae, Machairodontinae) from the Late Miocene of Spain: implications for the origins of the machairodont killing bite.” Zoological Journal of the Linnean Society, Vol. 144, No. 3, (Jul., 2005) pp. 363-377

Salesa, M.J., et al. “Inferred behaviour and ecology of the primitive sabre-toothed cat Paramachairodus ogygia (Felidae, Machairodontinae) from the Late Miocene of SpainJournal of Zoology, Vol. 268, No. 3 (Mar., 2006), pp. 243-254

Simpson, G.G. “The Function of Saber-Like Canines in Carnivorous Mammals.” American Museum Novitiates, August 4, 1941

Therrian, F. “Mandibular force profiles of extant carnivorans and implications for the feeding behaviour of extinct predators.” Journal of Zoology, Vol. 276, No. 3 (Nov., 2005), pp. 249-270

Therrian, F. “Feeding behaviour and bite force of sabretoothed predators.” Zoological Journal of the Linnean Society, Vol. 145, No. 3 (Nov., 2005), pp. 393-426

Van Valkenburgh, B., and Molnar, R.E. “Dinosaurian and mammalian predators compared.” Paleobiology, Vol. 28, No. 4 (Dec., 2002), pp. 527–543

Walker, Alan. “Mechanisms of honing in the male baboon canine.” American Journal of Physical Anthropology, Vol. 65, No. 1 (?, 1984), pp. 47 – 60

Wroe, S., McHenry, C., and Thomason, Jeffery. “Bite club: comparative bite force in big biting mammals and the prediction of predatory behaviour in fossil taxa.” Proceedings of the Royal Society B, Vol. 272, No. 1563 (Mar., 2005), pp. 619-625





The Chimpanzees of Mt. Assirik

25 09 2007

When chimpanzees (Pan troglodytes) appear in documentaries they are often shown inhabiting relatively dense tropical forest, their lives taking place within the green refuge of the forests. As with any other species that is spread over a considerable distance, however, different populations of chimpanzees have different habits, and one of the most remarkable populations are those around Mt. Assirik. Located in the southeastern part of the Parc National du Niokolo-Koba in Senegal, the chimpanzees in this area have to deal with a local ecology that is drier and more open than some of their relatives elsewhere, and their behavioral adaptations to the environment is of great interest to those study human origins.

The Mt. Assirik study area is remarkable in that 55% of the habitat is open grassland, only about 37% being woodland of varying density and only 3% being more dense forest (the remaining area being made up of bamboo forest and isolated trees). Such open spaces allow some of the major Carnivora of Africa to live in close proximity to the chimpanzees; Lions (Panthera leo), Leopards (Panthera pardus), Wild Dogs (Lycaon pictus), and Spotted Hyenas (Crocuta crocuta) are all frequently seen in the area. As if having so many predators at their doorstep were not enough, the Mt. Assirik area seems to have fluctuations of food that aren’t correlated with seasonal changes, and in the dry season water is the most prized of any resource. The apes are not entirely helpless in the face of such pressures, however, and they’ve been behaviorally adapted in some very interesting ways.

Given a choice, the Mt. Assirik chimpanzees prefer to spend their time in the denser areas of forest, but shifting food resources sometimes require them to move across large expanses of open grassland in order to find nourishment. Wandering out onto the open plains alone is so dangerous as to nearly be suicidal, and the apes form large mixed groups when they have to move across the plains. During this time they are at their most vulnerable, especially since they would be unlikely to outrun any of the major predators (especially those that hunt in packs), and they are extremely alert when undertaking such a journey. What is perhaps most striking of all, hearkening back to Raymond Dart’s “Savanna Hypothesis,” is the fact that the chimpanzees sometimes stand up to get a better look at their surroundings, potentially spotting predators before they get too close, although such an observation should not be taken as a sweeping vindication of Dart’s ideas of human evolution.

The presence of just one tree or a few trees spaced far apart doesn’t help the chimpanzees much either; mothers with children and individuals spent much less time in the sparser woodland areas than in the forest, mixed groups seemingly having to issues with the woodlands. Why should this be so? Well, leopards can climb trees (and often do so to stash their kills), as well as lions, and so simply climbing a tree does not equal escape. Lone chimpanzees are far more comfortable in a habitat where they can climb a tree and move through the canopy out of reach of their assailants, something that is not possible in woodlands. The predators may also have another effect on the diet of the chimpanzees; the Mt. Assirik chimps do not seem to eat young ungulates or monkeys, although such behaviors have been made famous where it has been observed (i.e. Gombe). This may be due to some competition, but it may also be due to the restricted forested habitat and the fact that chimpanzees would have to enter the habitat of the carnivores in order to capture young ungulates, predators being likely to quickly learn about any kills that had been made.

Indeed, the Mt. Assirik population is remarkable in that it often moves long distances in order to obtain food as it becomes available, relying on numbers and vigilance to protect itself from predators when it’s habitat only offers a few isolated islands of relief. Although humans did not evolve from modern chimpanzees, this population may give researchers some idea of the behavior patterns of our ancestors when faced with similar constraints when forests became sparser and the plains were filled with predators. Such social behavior is not the only thing that makes the Mt. Assirik chimpanzees stand out, however; they also make use of Baobab trees in a very interesting way.

By now many people are familiar with the ability of chimpanzees to use a piece of wood as a hammer to break a nut placed upon an “anvil” of rock or tree root; such footage has been shown in television programs again and again. Such behavior did not come out of nowhere, however, and the way Mt. Assirik chimpanzees open nuts may represent a stage of tool use that precedes the hammer-and-anvil technology. While it had been disputed for some time whether the Mt. Assirik population used hammers and anvils or just anvils, recent studies have shown that they are cracking open the hard nuts of the tree on branches and not using a hammer. While we might think of an “anvil” as something that can only be used in conjunction with a hammer, mechanically this isn’t necessarily so, and the Mt. Assirik chimpanzees bang the hard nuts they collect on the branches of the tree (therefore staying aloft, not coming down to use stones or the roots of the tree), the tree itself being the anvil.

Given the basal usage of anvils by the Mt. Assirik chimps and the use of hammers and anvils elsewhere, it becomes possible to hypothesize about the evolution of stone tool use in our own ancestors. The starting point was likely similar to what is exhibited by the Mt. Assirik chimpanzees, banging hard nuts on trees or rocks in order to open them (thus preventing damage to the teeth, if it even would be possible to open the nuts using their jaws). The next step would be adding a hammer, possibly wooden (as seen in some groups today) or possibly stone. At this stage any combination of wood or stone hammers and anvils could be used, but tool use would probably not progress until a population was using stone hammers and stone anvils to open foods. In such a scenario, the apes would sometimes miss their targets and flake off bits of stone, an accident that would shape the tools. When a certain cognitive leap was made, the apes could then move from accidentally flaking their tools to doing it intentionally to truly be making tools rather than making use of naturally occurring bits of wood and stone. The reality of the situation may be forever lost to us, ancient tool use before the knapping of stone became prevalent being notoriously hard to discern, but such a line of behavioral descent is not unreasonable and seems to allow further development merely by chance combinations of naturally occurring resources.

Such a discussion is only a brief sketch based upon what I have only recently learned myself, but I hope that it has been at least somewhat informative. Different populations of chimpanzees show different behaviors and live in differing ecologies, and it would be a mistake to assume what the famous Gombe chimpanzees are doing holds true for all the other populations. Another population that I soon intend to write about spends time in caves, probes trees for bush babies, and may even have the beginnings of a fire culture; others do not show the same exact behaviors, but they have their own cultures and reactions to the local ecology. While we should be careful in analyzing the living populations of chimpanzees and their perceived similarities to humans, it would be foolish to think that they can tell us nothing of our own past, and if very well may be that some of traits (behavioral or otherwise) they now exhibit were present in our own lineage, vignettes of evolutionary history being replayed with different actors in our own time.





Of feathers, nests, and dinosaurs

24 09 2007

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

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

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

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

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

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

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


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

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

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

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

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

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

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

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

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

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

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

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


Dromeosaur Phylogeny

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

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

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

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

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

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

References;

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

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

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

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

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

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

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

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

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

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

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





From the mind of G.G. Simpson

20 09 2007

George Gaylord Simpson is one of my most favorite scientists, and I think that only Stephen Jay Gould has had a larger impact on my intellectual evolution. Indeed, not only was Simpson a brilliant scientist, but he was a fantastic writer as well, and even though many of his books are no longer entirely accurate they are still a pleasure to read (his first book, Attending Marvels: A Patagonian Journal, is especially good). Given Simpson’s influence and accomplishments, it is of little surprise then that Leo F. Laporte has been considerable time researching the scientist, and in 1987 a selection of Simpson’s letters to his family was published under the title Simple Curiosity. While I have yet to finish the book, I found the following passage, from a letter to George’s sister Marthe dated Jan. 25th, 1926, especially interesting, and have reproduced the relevant parts of it here;

The reconstruction of the past, even so great a past as that which lies before me here, can add only a melancholy significance to the fact which we know but dare not realize that the present must become as truly past and perhaps even more irrevocably. As for science, one who is not engaged in it can hardly realize to what extent petty motives dominate even here. The highest possible scientific motive is simple curiosity and from there they run on down to ones as sordid as you like. And all our scientific interpretations and theories are simply meaningless. There are facts, of course, in any workable use of the term facts, but with us as with artists and other impractical people here facts are considered as only so much mud and straw unless they can be piled up into a hypothesis, gaily stuccoed and concealed with theory. And like other futile edifices of man these are inhabited for a brief space giving glory to the proprietor of the most unusual or striking and then left to melt back to dust and be forgotten, or worse yet, to become curiosities for generations with other “latests”.

Don’t think I am bitter or unhappy about my work. I like it very much and get pleasure out of it. I am also achieving considerable success. [emphasis mine]

As a friend and teacher once told me, science is continually undertaken for the next generation. While some researchers may have the pleasure of having their hypothesis accepted (or even vindicated) in their own lifetime, it is the next generation of scientists who will look at the information from a different standpoint, hopefully freer of the motives or trains of thoughts of those that trained them. In a moment of melancholy, this can be an awfully depressing thought, while in truth it is an amazing and liberating thing to know that even if hypotheses or ideas eventually die away, what each scientist brings to their discipline might be useful to later generations on inching towards the reality of the workings of nature. As Leo Laporte suggests in the introduction of the book, however, Simpson seems to have outlived his own influence, his fears of 1926 of being forgotten in favor of “the latest” being somewhat realized. In fact, it was not so much that his ideas were discarded, but rather that what he had done became so accepted that it was almost taken for granted, nearly divorced from Simpson himself (especially Simpson’s contributions to combating notions like vitalism, finalism, orthogenesis, and aristogenesis in evolution).

This particular letter also reflects worries that would haunt Simpson for the rest of his life; the fear of not being able to contribute to science, not receiving recognition for his work, and being forgotten as if he had never even existed. Such worries are perhaps most poignantly reflected in a book that G.G. never intended to be published; The Dechronization of Sam Magruder. The absolutely wonderful work, a short novella about the titular character cast back into the Cretaceous, allows as much insight into the scientist as any of his more straightforward letters, and in the Afterword Stephen Jay Gould (who knew Simpson personally) reveals that the lonely Sam Magruder is G.G. Simpson. Gould writes;

I knew Simpson during the last fifteen years of his life, when he was the most honored and the most revered paleontologist in the world. Yet I never encountered a man so apparently lonely (save for the comfort of immediate family), so dissatisfied, so craving so recognition, yet so incapable of satisfaction. I wanted to shake him (or hug him, if he would have permitted either) – and tell him how much we all loved him, how his work had been our chief joy and inspiration. But no one could find a middle ground to please him. One either spoke truly and therefore had, at least on occasion, to express some disagreement with something he had once said – and this he could not bear. Or else one played the toady and agreed with everything he said – and this he could bear even less, for his fierce intellectual honesty could not tolerate false ingratiation. And so, one of the world’s most honored scientists wallowed in a miasma of doubt and anger, always fearing that future generations would ignore him and that all his work would ultimately go for naught.

While I do not wish to “[wallow] in a miasma of doubt and anger” as I proceed through my intellectual evolution, whatever form it eventually takes as the years tick on, I can relate to Simpson’s worries. The more I seen to take in, the less I seem to understand (and the more questions seem to remain). Even though I continually try to take in more information about nature and how it works, my grasp of it is tenuous at best, although I can’t think of any more enjoyable pursuit than those that I engage myself in whenever time permits. As I had mentioned before, however, one can look at the ever-changing body of knowledge of science with disappointment and disdain, or with hope that what we do today will allow future generations to come that much closer to understanding. In Quest for the African Dinosaurs, paleontologist Louis Jacobs is frank about his own doubts involving his discoveries in Malawi & Cameroon; he has opened up new areas for exploration, but his particular analysis of the finds may or may not last. Before describing his last day in Malawi, Jacobs concludes that there is still a great need for scientists to study the ancient world he helped to uncover;

All of the studies done thus far are preliminary. More work needs to be done on everything. The frogs are unstudied, the mammallike croc is not yet named, nor are the Malawi-saurus [later officially named Malawisaurus] or our new species of diplodocid formally named. The stegosaur and theropods need detailed examination. What will they tell us? The questions go on and on. It will be years before the final reports are completed. It will be years before Elizabeth has turned in her finished dissertation and returned to her country to undertake new investigations in Malawi’s fossil beds. Even after that has happened, scholars will forever employ the specimens collected in our Malwai expeditions, and those from Cameroon, just as they use books in a library, for their own research purposes. Ideas will constantly be revised, eternally updated, never static. What we think now about Malawi-saurus and the other fossils from Africa is sure to change in the future. In one sense the means that what is being said today is sure to be wrong, or at best, not completely right; in a more important sense it means that what is being said now will help us be closer to the truth next time.

While the ultimate satisfaction of having a hypothesis vindicated (or the frustration of a beloved one being struck down) may escape many scientists for many years, there is satisfaction in contributing to science even if the analysis is incorrect. Perhaps this is why it is so enjoyable to be paleontologist, and why so many bone sharps like R.T. Bird could find in fossil hunting so much enjoyment without overly worrying about the more academic aspects of the field; even if an analysis is wrong, every bone that comes out of the ground helps to further the understanding of vanished worlds, the ever greater accumulation of material allowing each new generation of scientists to notice new ideas, refine old ones, and become ever more accurate if freedom of thought and inquisitiveness are allowed to persist. For my own part, I can’t think of any other line of inquiry I’d rather associate myself with, nor any other that sparks my imagination in quite the same way. If I ever will contribute to this science (or any other) will remain to be seen, but I am sure the feelings that I have expressed are not unique.





Amalgamated Anthro News

19 09 2007

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

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

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

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

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

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

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

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

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

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

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





A peek at my homework

19 09 2007

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

Summary

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

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

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

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

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

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





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

17 09 2007

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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