STL Science Center

STL Science Center

24 November 2012

To Allosaur or Not To Allosaur?

©Michelle (AKA Mitternacht90)
Saurophaganax, as we briefly discussed yesterday, poses a small problem. Looking at the skeleton, both from yesterday and today, it can be seen to possess many Allosaurid elements, especially in the claws and a vague resemblance in the top of the skull from the nasal back to the parietal; I think this may be an effect produced by the ridges and rugosities seen above the orbital fenestra as Allosaurus species were known to have such formations on their skulls as well. However, many theropods had a set of small nubs of horns or rugosities on the tops of their heads that bear resemblance to these, so we cannot use that as a piece of evidence that undeniably unites the two genera. Chure mentioned tibia characters that had been mentioned prior to his renaming of the genus, and subsequent separation from Allosaurus completely, but noted that these characters did not differentiate the two genera. Instead, he named characters of the neural arches of vertebrae in a sample labeled OMNH 01123 (Oklahoma Museum of Natural History) as a new holotype for Saurophaganax.

©Mineo Shiraishi
When it is fleshed out, however, Saurophaganax certainly resembles an Allosaurus in many ways. Part of the reason that we cannot easily tell the animals apart is due to the fact that the neural arches, which are used by Chure as a holotype and possess the characters used to separate the genera, cannot be seen in a fleshed out animal. What we are left with is a very Allosaurine dinosaur, which makes sense considering that Chure's classification of Saurophaganax still places the genus within the Allosauridae. Saurophaganax, then, would look somewhat like an Allosaurus in the same way that many hadrosaurs have similar characteristics within the same clade. The most notable, when fleshed out using the material available, is the similarity in the claws and those cranial rugosities and ridges. Considering Allosaurus' ability to use its own claws to take down prey it makes sense that a more "technologically advanced" member of the family would retain, and perhaps even fine tune, those weapons. The cranial protuberances were probably for species and individual identification as well as just plain looking beautiful along with that athletic Allosaur-like body.

©Nobu Tamura
This incarnation of Saurophaganax is a little more stylistic and gives us some more differences from Allosaurus. More than anything Tamura has highlighted increases in body size around the base of the skull, the base of the tail, and even given our typically agile looking Allosaurid frame a bit of girth. The size increase between Allosaurus and Saurophaganax, supposedly, was quite significant, and as such the agility of Allosaurus may have been lost to the later Saurophaganax which may have hunted using its sheer size to aid in taking down larger prey that were either slower moving, such as older sauropods, or it may have been more of an ambush predator whereas earlier Allosaurs were thought to have been able to run down some prey items and use their agility. Gigantism to wrestle prey items would not be a new idea in carnivore circles as many other theropod family possess, usually, either earlier or later members that seem to have been designed for that exact purpose (think of Utahraptor, Acrocanthosaurus, and Carnotaurus as examples of bulky wrestler-like theropods). Perhaps this is something that should be considered when thinking of the larger Saurophaganax.

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