What big teeth you have…

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.

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

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-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.

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;

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.

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.

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.

The skull of Smilodon on display at the AMNH.

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

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

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.

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.

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 fatalis” Journal 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 Spain” Journal 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

Philadelphia Zoo Photos, Pt. II

As promised, here is the second set of the better photos from my trip to the Philadelphia Zoo. I probably should (at the reccomendation of several commentors) register with Flickr and upload the lot of them, but that will have to wait until tomorrow (I’ll also go back and do likewise for the pictures on this computer as time permits). Let’s pick up where we left off, with one of my most favorite of big cats, the Amur Leopard (Panthera pardus orientalis);

There is nothing quite so beautiful as the emerald, fiery stare of an Amur Leopard. The eyes of almost any big cat can be described as intense or as being as intricate as a precious stone, but there is something about the gaze of leopards that strikes me in an entirely different way than that of their cousins…

…yet even the most majestic and feline predators needs to make time for a brief tongue-bath every now and again.

It’s amazing the amount of bravado an inch or so of glass can produce. The object of the leopard’s stare was a child that could not have been more than two years old, being held up to the glass by his parents to get a closer look at the “big kitty.”

At times the leopard seemed just as interested in what I was doing as I was in his activities.

It is sad enough that this leopard is among the last of his kind anywhere in the world, being the most endangered of all the big cats. Why he is left on display in isolation, with not even as much as a plaque explaining what species he is and the problem those still in the wild face, not to mention the (as far as I can ascertain) the lack of a breeding/conservation program, confuses and frustrates me.

The Giant River Otter (Pteronura brasiliensis) were also released just as my wife and I reached their enclosure. They certainly seemed excited to be out in their habitat, full of fish for them to snack on.

At one point something apparently spooked the group, and they engaged in a “mobbing” behavior similar to that seen in the BBC’s Planet Earth series when a group of otters of another species faced a Mugger Crocodile. What the disturbance was, I couldn’t tell, but it seemed to come from the other side of their enclosure.

Unfortunately WordPress was a down for a little while last night so I didn’t get to upload the rest of the pictures, but I will do so during a break between my classes in a few hours. Snuggling Aardvarks, primates (from prosimians through apes), and mammalian herbivores of various description.

Photos from the Philadelphia Zoo, pt. I

As promised, here are some of the better shots from yesterday’s visit to the Philadelphia Zoo. I’m sorry to say that I’m going to soon write up something about the Zoo’s shady dealings involving it’s African Elephants (visit Help Philly Zoo Elephants for a spoiler), but for now I’m going to focus on some of the better photos out of the 500+ I shot yesterday. And away we go…

I absolutely love this fountain.

While not particularly exotic, Scottish Highland Cattle are still pretty neat.

A pair of rare Blue-Eyed Lemur, Eulemur macaco flavifrons. The black one is the male, the blonde the female, and they were very excited at the prospect of a snack (the mangabey next door was getting ded fed at the time)

One of my most favorite of all mammals, the Giant Elephant Shrew (Rhynchocyon petersi).

This, by far, was the thinnest Mara (Dolichotis sp.) I think I have ever seen.

The Galapagos Tortoise (Geochelone nigra) were just beginning to stir when we arrived. They weren’t nearly as randy as they had been during our last visit (I thought I had heard it all until I hear the deep tones of tortoise-lovin’)

An African Elephant (Loxodonta africana) that we were told was named “Petunia” was also up and about. The Philly elephants will soon be moved out of their rather meager accomodations, although it might not necessarily be for the better.

This little male Amur Tiger (Panthera tigris altaica) really loved his tire. He wouldn’t let any of his brothers near it without showing his annoyance.

The strangely white female lions were relaxing in the early-morning shade. I know that their condition is a regional variation, although I forget the details at the moment.

Some of my most favorite Carnivores, White-Nosed Coati (Nasua narica) were scrounging for insects and other morsels when we passed by their enclosure.

And, just for Jeremy, a Red Panda (Ailurus fulgens).

We also came across the most evil-looking Caiman I had ever seen (there was no ID plaque, so I’m not sure what species it was).

And the Clouded Leopard (Neofelis nebulosa), as ever, was asleep in it’s hammock. I have never seen this cat move a muscle in my four visits to the Philly Zoo thus far.

Just around the corner, however, was a much more active and curious cat; a male Amur Leopard (Panthera pardus orientalis). He is one of the most beautiful big cats I think I have ever seen, and it’s a shame that he’s essentially “locked up” in his enclosure, and as far as I know the zoo does not keep a female Amur Leopard to run a breeding program for this most critically endangered cat.

I still have at least 25 pictures to share, but you’ll just have to wait a little bit longer for them. Check back later tonight for more of our friend the Amur Leopard, some Giant River Otter, White-Handed Gibbons, and plenty more.

Mine!

My trip to the Philadelphia Zoo this morning presented lots of great photo ops, especially in the morning. I’ll post more of the plethora (500+) of pictures I took tomorrow, but here’s a bit of a teaser. First, the three male Amur Tiger cubs born recently. The one in the middle really loved his tire;

The male Amur Leopard also was very curious about what I was doing on the other side of the glass, being much more active than on previous occasions when I have visited (expect a larger post on Amur Leopards and their plight in the near future);

Thylacoleo carnifex, ancient Australia’s marsupial lion

My home state of New Jersey is the epitome of suburban sprawl, McMansions and cul de sacs being about as common as the White-Tailed Deer that take advantage of the grass and brush on the side of the Garden State Parkway year round. There is seemingly no place you can go in the state where the rumble and roar of traffic cannot be heard, although the sprawling network of impervious surface does allow for easy travel to almost anywhere in the “Garden State.” On these roads, usually on warm summer nights, you’re likely to see what appears to be a large white rat shuffling across the lanes. While there are no hackneyed jokes that I know of about the Virginia Opossum crossing the road (“To eat your garbage” would be the most realistic answer), the critters turn up as roadkill quite often, not a very dignified end for the only marsupial mammal to live north of the Rio Grande in North America. While the scruffy Virginia Opossum represents the whole of marsupial mammals in the U.S., it has many close relatives throughout South America (Order Didelphimorphia), and is a bit more distantly related (but still close) to the Australian “possums” (Suborder Phalangeriformes), the marsupial forms of “the island continent” being perhaps the most familiar and oddly charismatic of any members of the Infraclass Marsupialia.

A Red Kangaroo (Macropus rufus) at the Philadelphia Zoo (taken in February, 2007). The Red Kangaroo is probably the world’s most recognizable living marsupial mammal.

Much like any group of living mammals, however, the fossil record of marsupial mammals is full of bizarre forms that have left no living descendants. We should not regard such lines of extinct fauna as somehow inferior or flawed, however. As famed paleontologist Stephen Jay Gould once wrote in his book Wonderful Life;

First, in an error that I call “life’s little joke”, we are virtually compelled to the stunning mistake of citing unsuccessful lineages as classic “textbook cases” of “evolution.” We do this because we try to extract a single line of advance from the true topology of copious branching. In this misguided effort, we are inevitably drawn to bushes so near the brink of total annihilation that they retain only one surviving twig. We then view this twig as the acme of upward achievement, rather than the probable last gasp of richer ancestry.

I can scarcely think of a better example of this notion of the spectacular diversity of past life than the extinct marsupial Australian Megafauna, and the carnivorous Thylacoleo carnifex would remind any fossilist that just because an animal is extinct, such status does not imply that it was not a terror in its heyday. Deemed the “Marsupial Lion” Thylacoleo carnifex developed many of the predatory adaptations we seen in living big cats (hence the “leo”, meaning “lion”, in the genus name), and despite the superficially rodent-like appearance of it’s front teeth, it was certainly a powerful predator.

In order to understand why Thylacoleo was such a formidably hunter we first need to understand something about living Carnivora (civets, otters, cats, dogs, bears, etc.) and the way their teeth were arranged. While their have been many large carnivorous mammals since in the past 65 million years, carnivores are set apart by their carnissal, or “scissor”, teeth. If we look at the massive skull of the predatory mesonychid Andrewsarchus of the Eocene, for example, the front teeth appear useful for piercing but the teeth further back in the jaw a large and a bit blunted. While useful in tearing flesh from bone and crushing, they were not especially well-adapted to cutting slicing flesh and such creatures probably ate a fair amount of bone (and possibly had problems with bone splinters in their gastrointestinal tracts) as well.

The only known skull of Andrewsarchus, on display at the American Museum of Natural History in New York City. Note the large, blunted teeth towards the back of the jaw.

The likely ancestors of today’s extant carnivores had their start long before Andrewsarchus was roaming what is present-day Asia. Miacids were weasel-like mammals and are known from the Paleocene and Eocene epochs, and are the first mammal group known to have teeth called “carnissals.” These are the teeth that group all living carnivores together, robust and pointed teeth that seem to be essential to consuming flesh. Another group of mammals, the creodonts (the first of which were discovered by E.D. Cope), also possessed carnissal teeth, but their line died out about 8 million years before the present. Still, the success of the carnivorous mammals seemed to depend on the specialization of the some of the premolar and molar teeth into a sharp, cutting edge, commiting many of the group to a strictly carnivorous lifestyle. Cats are the most specialized today, as they have lost some teeth in the front of their jaw in order to allow their dagger-like canines to have the maximum effectiveness and they no longer have flattened molars at the back of their jaw like canids (dogs) have, allowing those animals a little bit more of a diverse diet in tough times. Indeed, overspecialization in a predatory niche, called “hypercarnivory,” can often put a species at risk if they cannot effectively process other food sources if prey stocks dwindle (such a hypothesis has been put forward about the recent “bone-crunching wolf” discovered in Alaska).

A replica of the skull of Thylacoleo, on display at the American Museum of Natural History.

Thylacoleo, however, was an entirely different branch of the mammalian tree, but it seems that its skull and jaws were adapted to similar ends (although arguably were more extreme in their modifications). As easily seen from the skull of Thylacoleo, this marsupial predator was adapted to have it’s own fearsome shearing teeth. The premolars essentially became laterally-compressed blades, more high-ridged and pointed at the front, yet still sharp all the way down their length. These teeth in the upper and lower jaw even helped to sharpen each other as they slid past, allowed the predator to retain a sharp edge. Flattened teeth that might be useful for grinding or processing other foods are entirely absent behind the premolars, showing the Thylacoleo was a specialist of the highest order, having much more scissor-like teeth than the placental carnivores on other continents. Such a gape would have been absolutely fearsome, as exemplified by this recent reconstruction by Jeanette Muirhead;

Thylacoleo carnifex, used with permission of artist Jeanette Muirhead.

What is even more surprising than the blade-like teeth of Thylacoleo, however, is how strong its jaws were for a creature of its size. A recent study by Wroe, McHenry, and Thomason found that Thylacoleo, a predator that was less than four-feet long and probably weighed only 220 pounds, had the a bite force equivalent to a modern lion twice its size. The unusual dental arrangement of its jaw might have mitigated this somewhat and technical trials still have to be carried out, but if what the researchers found holds then Thylacoleo could probably have preyed upon most animals living in its range up to sub-adult size on its own, perhaps being the fiercest mammalian predator ever known.

How did Thylacoleo attain such high bite forces? The answer might have to do with the brain and skull differences between marsupials and placental mammals. Many carnivores have relatively large brains in comparison with marsupials, lessening the amount of bone they can devote to massive muscle attachments to enhance bite force. Thylacoleo, by contrast, seems to have had stronger muscle attachments and a smaller brain, and it’s skull superficially resembles that of a big cat. While canids often have elongated skulls, cats have foreshortened ones, and oddly enough Wrote and his colleagues seem to have found that carnivorous mammals that are known to be bone crunchers (primarily dogs or dog-like carnivores) appeared to have overall weaker bite forces than those that did not have the same osteophagous tendencies. This may have to do with the actual killing of prey, big cats and similarly-designed predators depending on strong bite forces in order to choke their prey to death or tear out a large chunk of the prey’s neck with a jugular bite. There are exceptions to this, the bite of saber-toothed cats often being calculated as relatively weak, but overall it seems that a shorter skull with a deep mouth is better of achieving high bite forces than a longer and narrower one. Hence, Thylacoleo actually is not a bad name for the “pouched lion”; it seems to share a large amount of convergences with its modern-day namesake, although it may have been less bright (and less sociable) with a more powerful bite.

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.

The predatory affinities of this animal did not always seem so obvious, however. Paleontologist E.D. Cope, in a paper entitled “The Tertiary Marsupiala,” recaps some of the controversy about the feeding habits of Thylacoleo that formed in the late 1800’s;

The discussion between Professor Owen on the one side, and Messrs. Falconer, Krefft and Flower on the other, as to the nature of the food of Thylacoleo, is known to paleontologists. From the form of the teeth alone, Professor Owen inferred the carnivorous nature of the food of this genus, while his opponents inferred a herbivorous diet from the resemblance between the dentition and that of the herbivorous Hypsiprymnus. I have pointed out that the comparison of Thylacoleo with Hypsiprirnnus is weakened by two considerations :

First, the cutting teeth in the two genera are not homologous ; second, the grinding series of molars, complete in Hypsiprymnus, is almost wanting in Thylacoleo. It evidently does not follow that because Hypsiprymnus is herbivorous Thylacoleo is so also. Professor Flower refers to the reduction of the molars in Thylacoleo as slightly complicating the problem, and concludes that the food of that animal may have been fruit or juicy roots, or even meat. It is difficult to imagine what kind of vegetable food could have been appropriated by such a dentition as that of Ptilodus and Thylacoleo. The sharp, thin, serrate or smooth edges are adapted for making cuts and dividing food into pieces. That these pieces were swallowed whole is indicated by the small size and weak structure of the molar teeth, which are not adapted for crushing or grinding anything but very small and soft bodies. It is not necessary to suppose that the dentition was used on the same kind of food in the large and the small species… In Thylacoleo carnifex it might have been larger eggs, as those of the crocodiles, or even the weaker living animals. The objection to the supposition that the food consisted of vegetables, is found in the necessity of swallowing the pieces without mastication. In case it should have been of a vegetable character the peculiar premolar teeth would cut off pieces of fruits and other soft parts as suggested by Professor Flower, but that these genera could have been herbivorous in the manner of the existing kangaroos, with their full series of molars in both jaws, is clearly an inadmissible supposition.

I have to agree with Cope; it is hard to imagine what sort of vegetable matter Thylacoleo would be eating with its specialized dentition. It would have been able to chop plants, surely, but whatever food was not inside the mouth would fall into the ground, that inside the mouth would have to be swallowed whole. This would results in Thylacoleo chewing much more low-quality plant food than other animals with teeth adapted to herbivory, and I doubt that Thylacoleo had a caecum or a habit of swalling smooth stones to aid in the digestion of the hypothetical greenery. Even in 1969, however, there seemed to be some doubt as to whether Thylacoleo was a herbivore, an omniovore, a carnivore, or a hypercarnivore. Leigh Van Valen, in the paper “Evolution of Dental Growth and Adaptation in Mammalian Carnivores”, wrote;

The jaw musculature of Thylacoleo was generally similar to but more powerful than that of Trichosurus, but whether all this increase was an adaptation to greater size is unknown. The question of the diet of Thylacoleo is unresolved. If Thylacoleo was carnivorous, it was in several respects a relatively inefficient carnivore. However, large carnivores were rare in Australia, and the condition of Thylacoleo is what would be expected if a Trichosurus-like phalanger became carnivorous. But the herbivorous diet advocated especially by Flower, Krefft, Lydekker, Charles Anderson, and Gregory remains a real possibility. A decision on this matter will probably not be possible until there is adequate knowledge of the appendicular skeleton.

The initial descriptions of Thylacoleo by Richard Owen were more certain of the carnivorous habits of the marsupial, however. One December 16, 1858, Owen’s paper “On the Fossil Mammals of Australia. Part I. Description of a Mutilated Skull of a Large Marsupial Carnivore (Thylacoleo carnifex, Owen), from a Calcareous Conglomerate Stratum, Eighty Miles S. W. of Melbourne, Victoria” was read before the Royal Society. It states;

The evidence of a large carnivorous marsupial, from pliocene formations in Australia, reached me not many years after my determination of the still larger herbivorous marsupial, Diprotodon australis, which first suggested the idea of the coexistence. The evidence was received in the year 1846…

The fragmentary skull of Thylacoleo from Owen’s paper “On the Fossil Mammals of Australia. Part I. …”

The initial fragmented skull of Thylacoleo carnifex (Owen), pictured above, was obtained and sent to the great naturalist by Dr. Hobson of Melbourne. Upon receiving the fossils, it seems that Owen almost immediately recognized the convergences in the skull with modern carnivores, the extant lion (Panthera leo) being his foil for the characters in the new skull. Owen describes the deterministic state and characters of the skull as follows;

The ‘skull’ consisted of the cranial part, similar in size and in the development of the temporal ridges and fossae to that of a Lion. The ‘incisor’ was a large tooth with a trenchant or incisive crown, implanted, with a small tubercular tooth, in a portion of the right superior maxillary bone, including part of the orbit and lacrymal bone. The latter specimen gave decisive confirmation of the carnivorous character of the fossil, the ‘incisor’ tooth answering in shape and function to the great sectorial or ‘carnassial’ and the tubercular tooth to the small tubercular molar of the Lion; being situated, as in that animal, on the inner side of the back part of the sectorial tooth.

Indeed, the bladelike teeth alone were enough to convince Owen of the ferocious nature such an animal must have possessed, writing;

In existing carnivorous mammals the ferocity of the species is in the ratio of the ‘carnassiality’ of the sectorial molar, i. e, of the predominance of the ‘blade’ over the ‘tubercle;’ and this ratio is shown more particularly in the upper sectorial, in which, as the tubercular part enlarges, the species becomes more of a mixed feeder, and is less devoted to the destruction of living prey. From the size and form of the carnassials of Thylacoleo, especially of the upper one, we may infer that it was one of the fellest and most destructive of predatory beasts.

A second, more complete skull of Thylacoleo carnifex, from Owen’s paper “On the Fossil Mammals of Australia. Part II. Description of an Almost Entire Skull of the Thylacoleo carnifex, Owen, from a Freshwater Deposit, Darling Downs, Queensland”

Owen’s assertions did not go unchallenged, however. In a later 1886 paper “Additional Evidence of the Affinities of the Extinct Marsupial Quadruped Thylacoleo carnifex (OWEN),” the anatomist includes a quite humorous remark in response to one of his critics. As noted before, some scientists believed that Thylacoleo was essentially a living Cuisinart specializing in cutting up fruit, no more terrifying than some of the arboreal relatives of the Virginia Opossum noted above. Owen, in classic style, writes;

These eminent authors received the support, in reference to objections to my conclusions, of the (then) Curator of the Australian Museum, Sydney, Mr. GERARD KREFFT, who, in his contribution to the ‘Annals and Magazine of Natural History,’ series 3, vol. 18, 1866, p. 148, records his opinion that “the famous marsupial Lion was not much more carnivorous than the Phalangers of the present time.”

The species of carnivorous Phalanger is not named. No evidence of such by fossil specimens has reached me, nor have I found such exceptional habit of an existing species of Phalangista elsewhere noted.

Lower jaw (outside view) of Thylacoleo carnifex, as seen in Plate I of Owen’s “Additional Evidence of the Affinities of the Extinct Marsupial Quadruped Thylacoleo carnifex (OWEN)”

Indeed, armed with a more complete lower jaw of the animal, Owen even further extrapolated its carnivorous habits, postulating that it had been the “check” on the large herbivores known from the same period in Australia. All the large forms, in Owen’s view, ceased to exist when “bimanous” forms came to the continent, either eliminating Thylacoleo or putting it out of a job through competition, although the wholesale slaughter of Australia’s megafauna by the people who would become the Aborigines is not an open and shut case. Even beyond the skull, Owen was provided with a claw complete with retractable teeth, now known to occupy the “thumb” position of this carnivore. Some have speculated that its size, ferocity, and retractable claw allowed it to climb trees like a leopard, although others have doubted this an account of how robust Thylacoleo probably was (being twice the weight of modern leopards), which 1) would have made it difficult to climb trees, and 2) would have allowed it to chase off most of the competing predators/scavengers of it’s day. I doubt that there were many creatures that would have crossed the path of Thylacoleo and survived if the “pouched lion” was hungry or territorial.

Despite it’s fearsome reputation, Thylacoleo seems to have disappeared from the land “down under” around 40,000 years ago, probably the very last of its lineage. Indeed, while I have primarily focused on Owen’s T. carnifex here, there were many other earlier species and related genera, each showing different aspects of the skull and form. Why these bizarre creatures, once so prominently disputed, have disappeared from the public understanding of paleontology I cannot say, but it is probably to the relief of living kangaroos and other Australian fauna that they are long gone.

Partial skull elements, most notably the incisors, from Owen’s paper “On the Fossil Mammals of Australia. Part IV. Dentition and Mandible of Thylacoleo carnifex, with Remarks on the Arguments for Its Herbivority”

Photo of the Day: Cold Cougar

I originally posted this photo last January, way back when I had all of two readers, so I thought I would bring it back up front. This is one of the cougars at the Philadelphia Zoo’s “Big Cat Falls” exhibit, and the three cougars in the exhibit seem to love to hang out right in front of the glass. If you can get there early on a cold day when the glare isn’t so bad, the photo opportunities can be fantastic.

Finally, a story about “real” tigers

Zeff, a 13-year-old Amur (Siberian) Tiger at the Bronx Zoo (Taken February 2007)

A zoo in Romania is now home to two new tiger cubs, Lenuta and Costel, and it appears that their mother is caring for them. This story reminded me that the Philadelphia Zoo recently had some luck with its tiger-breeding program as well, with three tiger cubs being born this past spring as well (you can read more at the zoo’s official blog).

Rasi, one of the cheetah trio at the Philadelphia Zoo (taken January 2007)

There may be some cheetah cubs on the way at the zoo soon too, the brothers Micah, Rasi, and Spidi getting some female companionship in the near future. I haven’t been back to the Philly Zoo since February so I don’t know if the female has arrived or picked her mate yet, but I’ll definitely keep my eyes open for any news.

Splitting lumps, lumping splits, and other taxonomic shenanigans

This past March I blogged about a Nature article in the special “Linnaeus issue” involving the problem with determining what actually constitutes a species. In fact, the very same day I also mentioned that a new species of Clouded Leopard (Neofelis diardi)was recognized in Indonesia, on which Darren of Tetrapod Zoology provided a much more thorough history. Now, as Rich at evolgen points out, a new PLoS editorial is suggesting that we take greater care in name (or renaming as the case may be) mammalian species.

Bornean clouded leopard (Neofelis diardi)
Kalimantan (Indonesian Borneo), Indonesia.
CREDIT: (c) WWF-Canon / Alain COMPOST
IMAGE No.: 112939

The authors of the opinion piece, Meiri and Mace, criticize biologists who split species because two or more populations of one species simply do not overlap (either caused by some barrier separating them over a distance or ranges abutting without overlapping). Regarding the caramel-colored clouded leopard, they write;

In resurrecting N. diardi, Kitchener et al. are relying on the phylogenetic species concept whereby species are defined as groups that share at least one uniquely derived character. They distinguish two clouded leopard “species” solely on the basis of pelage (fur color and pattern) characteristics, despite the fact that differences in hair color often reflect minor geographical varieties in many mammals. Borneo and the Malay Peninsula differ in several biotic and abiotic factors. Thus genetic and morphological differences between populations of the 144 mammalian species they share are to be expected, and there could potentially be equivalent evidence to merit specific status for all of these; an outcome that would certainly be unjustified.

Indeed, populations of one species existing in relative isolation from each other is not enough to gain a new species status (if that were true, we’d have many more species of White-Tailed Deer and Cougars throughout the Americas at the moment), but such differences do lead to allopatric speciation events, regional differences showing up over time as local ecologies become more distinct from each other. Such considerations, however, would essentially negate designation of new species by skin/feather/hair color alone, being that the colors or patterns of a particular species can vary without there being any other distinctive features (while perhaps still meeting the requirement of one “derived” character).

Species designation is not all about being objective, however, the designations of species and subspecies inflating or deflating the raw numbers of local biodiversity and having an impact on endangered species status. If, for example, an island is deemed not to have just one large population of a particular species but two populations of two slightly distinct species, then the overall numbers for these organisms fall and may incite groups to try and protect them. A subspecies or local variation is far less likely to gain protection than a distinct species, so splitting is a way in which some people could possibly ramp up the overall biodiversity count (therefore reducing the number of individuals in populations), in turn receiving more aid than others. I have heard this charge made many times, although I have not seen much actual evidence that this is the case (see this opinion piece from the April 2004 edition of Current Science).

So what about the renamed Clouded Leopard Neofelis diardi? What differentiates it from the species to which it previously belonged, Neofelis nebulosa? Fortunately, I was able to access the article “Geographical Variation in the Clouded Leopard, Neofelis nebulosa, Reveals Two Species” (available here)to have a look at the data myself. The researchers, using skins primarily from museums (2 being from private collections) comparing the pelage patterns of 57 clouded leopards (skulls were typically not associated with the skins, if available at all) in order to determine if there was some sort of geographical difference. The primary differences the researchers observed were described this way;

In summary, clouded leopards with large clouds (Neofelis nebulosa) tend to have fewer, often faint, spots within the cloud markings, and they are lighter in color, with a tendency toward tawny-colored fur and a partial double dorsal stripe, whereas clouded leopards with small clouds (Neofelis diardi) tend to have many distinct spots within the cloud markings, greyer fur, and a double dorsal stripe.

The reason for the striking difference in coat pattern may be due, the researchers hypothesize, to the Isthmus of Kra acting as a biogeographical barrier, essentially isolating the two groups of clouded leopards from each other. The differences don’t merely reflect inconsequential differences in variation (i.e. the authors of the PloS cite Merriam going overboard splitting bear species based upon the smallest differences), but rather a split that has caused a good amount of differentiation in the appearance of the Indonesian leopards. Hair color is not the only evidence backing up the split, however, mitochondrial DNA analysis (the research appearing in the same issue of Current Biology as the pelage paper) showing that the greatest genetic difference between the clouded leopards is that between the “mainland” species & subspecies and Neofelis diardi. What’s more, the difference between the two different clouded leopard species appears to be equal to or greater than the differences between other cat species, further supporting the differentiation of these leopards. The authors do admit, however, that their sample size was rather small and more study needs to be done, but the results we have as of now strongly suggest that there are two separate species of clouded leopard living in southeast Asia.

While Neofelis diardi is not yet officially recognized as a species (at least to my knowledge), I do side with those who regard it as a distinct species. Suggesting that the authors of the pelage study merely looked at a few coats and said “Gee, these look different” and attempted to create a new species is a bit disingenuous, and the current PLoS editorial does not address the genetic studies of Buckley-Beason, et al. other than to say they were carried out. Their point about taking great care to accurately distinguish species is well-taken, but they did little more than make a caricature of the Neofelis diardi studies, and they probably could have picked a better example (although the overall attention the clouded leopard story got would make it an obvious choice because of its visibility).

Given the complexity and diversity of species concepts, there will likely always be disagreements and arguments. Indeed, if we look at the history of life on earth, it’s probably a good thing the fossil record is fragmentary; if we had all the organisms that ever lived and could line them up according to direct ancestor/descendant relationships from the first life form to us, we’d probably have a hell of a time determining when to make a species division. In essence, we have given ourselves a designation of Homo sapiens, but millions of years ago, billions of years ago, our direct ancestors looked quite different than us and would receive very different names. Indeed, as much as taxonomy is helpful, sometimes I wonder if designations of extant species sometimes conflates the evolution issue, suggesting that “species” are end-products of evolution that do not continue to evolve (and if we have no close ancestors, that they came out of nowhere). How this could be helped/fixed, I do not presently know, at least outside of serious contemplation and study of the history of life on earth.

Photos from Cape May, NJ

Yesterday, my wife and I left at 3 AM to arrive at the most southern point/beach in New Jersey, arriving just after the sun began to rise.

And here is my lovely wife in the early morning light;

We also encountered some local wildlife before even setting foot on the beach or pathways along the dunes. Many birds rested in their large birdhouses, and a small toad sat on the bench outside the restrooms;

Once we set foot on the beach, there were already plenty of Laughing Gulls skittering about on the sand and trying to snatch some bait from early-bird fishermen;

Tracey and I also noted a strange blob bobbing about in the surf. It turned out to be a dead jellyfish;

We saw many more of the decomposing cnidarians on the beach that morning;

After taking a little snooze on the beach, we took a short walk on a path behind the dunes, watching an immature Great Blue Heron and an egret try to catch their breakfast;

Small rabbits also abounded along the shore, and we saw many over the course of the day;

Being that it was too early to head over to the docks for our whale watching tour, we stopped by the Nature Conservancy migratory bird refuge. While most of the birds were too far away or simply not present during our visit, I did spot a number of Red-Winged Blackbirds, and this particular fellow was especially robust and colorful;

This bright flower also caught our eye;

By the time was had walked the trail it was time for our cruise, although nothing much happened for the first hour or so (outside of being followed by some laughing gulls);

The whole trip did not turn out to be a wash, however, as we came across a rather large pod of Bottlenose Dolphins (15-20 individuals) feeding close to shore, right in front of one of John Wyland’s famous “Whaling Walls” (depicting a Humpback Whale, amongst other marine life);

After the overall mediocre cruise and stopping for lunch, we headed to the Cape May Zoo, where I finally got to see some live Pronghorns (previously the only ones I had seen were the stuffed ones at the AMNH);

And, of course, no zoo trip would be complete without seeing a Muntjac;

While I had seen Capybara in zoos before, I at long last got to see one swimming, as well;

As would be expected, the American Alligators were also cooling off in the water, albeit in a more stagnant pool;

The weather was rather hot, so the big cats (lion, cheetah, tiger) mostly stayed out of the sun (and therefore impossible to photograph). I did manage to get a few shots of the leopard and ocelot, however;

The animals in the African plains enclosures were a bit more active, however, including the Reticulated Giraffes and Grey’s Zebra (previously I had only seen Grevy’s Zebras);

While not as exotic, the raccoons and swift fox the zoo kept provided me with some decent shots as well;

Before leaving, we also stopped into the “World of Birds,” where I encountered this strange species with yellow waddles (and showed no fear or concern that I was photographing it from so close a range);

Not long afterwards, we ate our dinner and headed for home, overall being a good day in Cape May. I also wanted to include this picture of a deer I got a few weeks ago in Pennington, NJ, where I was petsitting;

Photo of the Day: Chilled Cheetah

This is one of a male coalition of three cheetahs at the Philadelphia Zoo, this photo being taken in the early afternoon on a cold January day. A female cheetah is going to be introduced to the zoo soon, so there may very well be baby cheetahs in Philadelphia soon.