Why do I bother?

5 10 2007

When I was a kid, one of my most-favorite videos was the Christopher Reeve hosted documentary Dinosaur!, a program filled with shots of fossils, interviews with experts, awesome stop-motion animation sequences, and host segments shot in the dim halls of the AMNH. I haven’t seen it in years, but I remember it so fondly that it makes me want to go out and buy a VHS player just so I can watch it again. There have been more recent documentaries that have take a similar strategy, like the Jeff Goldblum-narrated When Dinosaurs Ruled series, but Dinosaur! remains my favorite, and it’s a far cry from modern programming.

“Ooo… At 8 something called ‘The Land of Lost Monsters‘ is on. Do you want to watch it?” my wife asked. I should have said “No” and saved myself the pain. The recent trend in paleo-documentaries has been to use CGI and storytelling as much as possible, pushing the actual science further and further into the background. This trend started with Walking With Dinosaurs, which was alright for what it was, but it has spawned so many clones that I wonder when we’ll be able to actually have dinosaur documentaries be about science and not just CGI critters that don’t look half as good as their big-screen equivalents (i.e. the work of Weta in King Kong [albeit speculative] and Stan Winston’s work on the Jurassic Park series). For those who haven’t had the displeasure of seeing the program, the Land of Lost Monsters is a two-hour program about man vs. beast from the time of Australopithecus africanus to the Pleistocene. Rather than containing any educational content, the show is all about sensationalism, hominids being beset by ravenous monsters throughout history. The treatment of Neanderthals as only cold-loving super-hunters that craved mammoth flesh was enough to make me roll my eyes, and the analogy “Neanderthals were to humans what the saber-tooth tiger was to a housecat” was enough to make me change stations.

What is strange about the current trend in pseudo-scientific television programming is that there are some people who still realize how to make a good documentary, even if it’s not prominently shown on the air. For instance, I didn’t particularly care for Walking With Prehistoric Beasts, but a companion documentary about the science behind the show (featuring interviews with many paleontologists) was fantastic. Likewise, the series Dinosaur Planet featured little “science breaks” here and there giving the audience some clue as what evidence the reconstructions were based upon. The interruptions were far from comprehensive, but there was at least the recognition that scientific reality should be addressed. I won’t go into the Nigel Marvin Chased by… and Prehistoric Park nonsense as I don’t want to go sailing off on a more vicious rant than necessary here.

At this point I should probably mention why I torture myself with shows I know are just going to be repackaged sensationalism with little scientific content. While I am trying to educate myself more and more about the scientific points of paleontology, I also am very much interested in the public perception of dinosaurs and other prehistoric creatures in paintings, drawings, sculpture, television, movies, amusement park rides, etc. All contribute (not always helpfully) to the public understanding of creatures that are no longer around to be viewed, at least not with flesh on. When someone creates a 3-D model of a Tyrannosaurus I am curious as to what it will look like, how it will move, what behavior the producers will make it perform, etc., and I am very concerned with the move towards “edutainment” on many of the “science” networks like TLC, the Discovery Channel, and the National Geographic Channel. Good programming is seemingly few and far between or generally less-promoted than the expensive rubbish that is constantly generated, a good documentary on the juvenile Tyrannosaurus “Jane” and a stunning documentary about lions & buffalo in Botswana (Relentless Enemies, to which there’s a beautiful companion book) receiving much less attention than pure B.S. about Bigfoot and “Hogzilla.”

To sum things up a bit, I feel that current paleo-programming all-too-often cheats the audience by hiding the science (or even distorting it), making it appear that all the problems have been solved and we now know everything about these animals. Documentaries that are supposed to be educational are more like B-grade monster movies, only they’re not nearly as fun to watch. As discussed in the comments of The Ethical Palaeontologist as well, many spectacular paleontological finds that are being published in Nature or Science seem to be little more than brief announcements, and it can only be hoped that the specimens will be more fully studied and described (as is the case with the strange theropod Majungatholus from a few years back). Perhaps I could use these problems as a way to launch into the whole “framing” issue, but I think I’ll leave that sleeping canid lie for the moment, although misrepresentation or oversimplification of paleontology to the public is nothing new.

This post shouldn’t be taken as a cranky call to return to some of the methods of paleo-documentaries of the 80′s and 90′s, however, even though I wonder what a modern day equivalent of “Mesozoic Mind” would look like (hat-tip to Neil for unearthing the video);

And while we’re at it, here’s another video that’ll probably bring back memories for some readers, and see this previous post for even more;





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 Boneyard #6

1 10 2007

The 6th edition of The Boneyard is now up at Fish Feet for your enjoyment. It’ll be back again in two weeks over at microecos, so keep your eyes peeled for great paleo-posts over the next two weeks.





Friday Morning Notes

28 09 2007

The amount of reading I normally am able to get accomplished has suffered greatly this week; I’ve read bits and pieces of a few different books but I haven’t been able to rip through works at my usual pace. This is probably just as well, however, as many of the books I was reading were more important to me in a historical sense (understanding what scientists thought about paleontology in the past), and most of the information was already familiar. Then, yesterday afternoon, Phil Currie/Kevin Padian’s Encyclopedia of Dinosaurs arrived, and it’s proven to be a very refreshing read. As is apparent to many readers of this blog, I definitely need to work on my anatomical understanding of dinosaurs (and tetrapods in general), and I have been learning a lot from what I was able to read last night (I read all the entries for “A” and “B”). Some of the entries are fairly technical and proved how much I still have to learn (like Currie’s entry on braincases), but others were more plainly written and I had a lot of “Aha! So that’s what that is” sort of moments. Such an entry was John Hutchinson and Kevin Padian’s entry for the clade Arctometatarsalia, and I definitely came away that entry with a more refined understanding of the arrangement of metatarsals and ankles in theropods. Spencer Lucas’ entry on Biostratigraphy was also very helpful, and so clearly written that I think nearly any reader would be able to understand it.

Given that the book is a amalgamation of work from various researchers and authorities, some entries are a little better than others, although so far I don’t have much to complain about. I know the book is a little dated (1997), but I’ve tried to keep recent changes I know of in mind as I read along. Although I am learning more about anatomy slowly but surely, I know that I’m now at the point where I really do have to get a textbook or other resource on skeletal anatomy (and I’m still waiting for the day when I can afford to purchase Romer’s Osteology of the Reptiles). Still, as I noted before, it’s refreshing to dive into a more technical scientific work and be able to get something out of it, and even though it might seem like a Herculean task I’m going to try and read the encyclopedia from cover-to-cover. After that I’ll probably take a “break” with something shorter, but I also want to try and read the whole of the 2nd edition of The Dinosauria, being that I’ve only been referring to it now and again when necessary. Once I’ve been able to do those maybe I’ll be able to move on to Gould’s 2,000+ page The Structure of Evolutionary Theory, but that might have to wait until winter break. Of course I’m saying all this now, not knowing what my life will be like in the coming weeks and months, but I think that I can do it (and I think I’ll greatly benefit from such an undertaking). The more I learn, the more I get sucked in, and I’m trying to teach myself as best as I possibly can.

I’ll be away for much of this weekend as well, my wife’s birthing falling on the 30th, and her chosen activity being camping up in New York. I’ll still write today and on Sunday when I get back, but on Saturday I belong to Tracey. There will still be plenty to enjoy in terms of paleo-blogging, however, with The Boneyard coming up at Fish Feet tomorrow, although I’m hoping my recent reading will help me in construction a better juvenile sauropod post when I get back.





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





8 things about me[me] returns

23 09 2007

Mark, of The Divine Afflatus fame, is back, and upon the occasion of his triumphant return has tagged me with the “8 Random Facts” meme. Although I was tagged by Bora back in June, I figured I might as well give it another go, especially since I would hope that there are least 8 more things of potential interest about me.

1) My wife and I drove down to Haddonfield, NJ today to visit the site where Hadrosaurus foulkii was discovered. I’m planning an uber-post about it’s discovery so I won’t go into those details here, but I have to say I was extremely disappointed with the “park.” After driving about an hour, we made our way through the suburban sprawl to a dead end, a commemorative plaque plastered to a rock sitting right across the street from a newly-built house. Thinking there must be something more to see, Tracey and I made our way down the embankment to the fetid, mosquito-infested and trash-ridden streambed below. While the Cretaceous marl was easy to locate, the only thing of note we found was a discarded Sears credit card. Further exploration was blocked by vast pools of stagnant water and the fact that the “park” was a patch of land surrounded by private property, the monotonous whir of a nearby lawnmower letting us know we were practically in someone’s backyard. Rather unfitting, overall, for one of the most important sites in the history of paleontology.

2) I heard the New Found Glory cover of Go West’s “King of Wishful Thinking” yesterday and I can’t get it out of my head (trust me, the NFG version is much improved over the original). The song can be found on the band’s new album From the Screen to Your Stereo II.

3) Although I would have normally waited for the paperback, I purchased the newest Terry Pratchett book, Making Money on Friday and have been reading it aloud to my wife. Although we somewhat fell out of the tradition, for the first 6 months or so of our marriage I’d read some Terry Pratchett to her every night before bed.

4) When I was in preschool I once played a Stegosaurus pitched in battle with Allosaurus during the ever-popular “Dinosaur Night.” While I was expected to lose, at the close of the confrontation I pleaded my case to the parents on scientific grounds that Allosaurus wouldn’t dare try and take down such a large and spiny critter, but my protest ended up being in vain. At least I got some dinosaur-shaped cereal out of it. (My later high school stage appearances included Eugene in Grease!, Mr. Kraler in the Diary of Anne Frank, and Father Drobney in Don’t Drink the Water).

5) Many people once had imaginary friends, but I had an imaginary enemy. Named “Snuff,” he was a demonic, shortened version of Sesame Street’s Mr. Snuffleupagus, and if touched by his trunk you would become paralyzed (and subsequently eaten). You know that high pitched whine you sometimes hear when a television is on even if you can’t see it? I thought that was the sound of his impending arrival, and I once heard it while riding my tricycle in the driveway. I abandoned my vehicle, which my mother ran over while backing out of the driveway, and although I did get in a bit of trouble spare parts were found and all ended well.

6) During the last year of high school and the first years of college I used to frequent the local clubs, seeing a punk/emo/ska band just about every other weekend. The first show I ever went to was for a local group called Shades Apart (they had a song, “Stranger by the Day,” on the American Pie soundtrack), although they are long defunct. The place that I saw them and many other bands, The Birch Hill, was torn down a few years ago, and now most of the shows are at The Starland Ballroom (although I haven’t been there in at least a year and a half).

7) Up until recently I wanted to study marine ecology at Rutgers, specifically what was happening to sharks off the NJ coast (no one seemed to be studying it, given the funding cuts to the EPA, DEP, and Fish & Wildlife in the state). When I told one of my professors about this he replied “What are you ever going to do with that? No one studies sharks” (which was the entire point, from my perspective). Frustrated with the academic wall I kept running into, I ended up taking a course in paleontology & “evolution and geologic time,” which definitely helped establish my current line of interest. Overall, I think I’m better for it.

8 ) This blog, as you and I know it, will soon become extinct. I know I’m using on of the oldest tricks in the book and that I’m terrible because I’m going to leave you all hanging (at least for a little while), but some big changes will soon be going into effect. I think you all will be pleasantly surprised, but for now mum’s the word. In time all will be revealed, but I’ll still be writing regularly until I can divulge the secrets in my possession.

So there you have it, 8 little tidbits of information that may or may not have replaced something more important that you were supposed to remember (i.e. the location of the car keys). Everyone who immediately comes to mind as far as tagging goes has already been tagged previously, so I’ll leave this one open ended; if you feel compelled to write, just leave a comment and I’ll set up the links. And now to finish up the scraps of reading I have left over…





Photos from the AMNH (yet again)

22 09 2007

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

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

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

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

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

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

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

Smilodon
A close-up of a more intact Smilodon.

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

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

Apatosaurus
The robust neck of Apatosaurus looms high above.

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

Apatosaurus
Apatosaurus from the rear.

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

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

Barosaurus
The head of a mini-reconstruction of Barosaurus.

Stegosaurus
The juvenile Stegosaurus model was pretty impressive, too.

Camarasaurus
A skull of Camarasaurus.

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

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

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

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

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

Edaphosaurus
The skull of the synapsid Edaphosaurus.

Elasmosaurus
The toothy jaws of Elasmosaurus.

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

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

Meteor
Perspective on a large, iron meteorite.

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

Triceratops
A close-up of Triceratops.

Tyrannosaurus
The most popular dinosaur in the museum, Tyrannosaurus rex.

Tyrannosaurus
The crushing jaws of Tyrannosaurus.

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

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








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