Weekly Wonders: Ulemosaurus

4 09 2009

Good tidings and well-wishes!

When it comes to diversity, few groups of Permian amniotes can hold a candle up to the dinocephalia, which sports such oddities as the ornately-horned hippo-like Estemmenosuchus, the predatory Titanophoneus, and the bizarre sexually-dimorphic Struthiocephalus (to which I must dedicate a post if I’m ever able to locate enough information). The latter creature hails from what is arguably the suborder’s most recognizable and interesting family: the thick-skull-ed, heavily-built Tapinocephalidae. Though by a wide margin the family’s most well-known and recognizable member is the South African Moschops,  for the purposes of this post, the spotlight will shift towards its somewhat more primitive Russian relative, Ulemosaurus svijagensis.

As always, before covering the anatomy and functional morphology of the animal itself, some taxonomic explanation is in order. The Tapinocephalidae belongs to the Tapinocephalia superfamily which also contains the mysterious Styracocephalus and the Titanosuchidae family (which harbors such eccentric members as Jonkeria and, unsurprisingly, Titanosuchus). Its members are defined by attention-grabbing tabular bosses (projections situated on the back of the skull) which point posteriorly, relatively weak and conical incisors & canines, a lengthy series of post-canine teeth, and well-developed palatal teeth (even on the vomer).  The group is otherwise notable for the fact that while other Dinocephalian clades (namely the Anteosauriaand the Estemmenosuchids) are known primarily from Russian deposits, the Titanosuchidae is chiefly composed of African genera.

Ulemosaurus skull replica.

Ulemosaurus skull replica.

According to Bernard Battail and M.V. Surkov in “The Age Of Dinosaurs In Russia And Mongolia” (which, as I’ve said before, is a vital resource for anyone interested in Permian amniotes despite its title) the Tapinocephalidae is recognized for

“Extensive cranial pachyostosis, leading to reduction in size of temporal fenestrae, jaw hinge displaced forward, incisors with well developed heels, canines reduced, [and] teeth interdigitating [(interlocked like the fingers on folded hands)].”

Ulemosaurusitself is currently represented by three skulls (which generally reach around .3 meters in length) and some very incomplete postcranial material which includes most of a shoulder girdle, a humerus, a radius, an ulna, and a few cervical & dorsal vertebrae. The creature (according once again to Battal and Surkov) is defined by the following characteristics:

“Very large [overall size]; snout narrow and tapering; skull wide and very high in postorbital region [(it gets wide and tall behind the eyes)]; thick cranial roof; strongly developed pachyostosis of dorsal border of orbit [(on the upper border of the eye socket)]; broad postorbital bar; temporal opening relatively large for a tapinocephalid, and, hence, relatively narrow intertemporal region; large incisors; medium-sized canines; anterior postcanine teeth much larger than posterior ones.”

Initially, the beast was thought to have been merely a new species of Moschops, however, most Permian workers now consider it to be far too archaic in comparison to be lumped together with its Southern relative.

Ulemosaurus reconstruction

Ulemosaurus reconstruction

Right then, on to the fun part: the functional morphology of Ulemosaurus. Palaeos.com has an excellent article on this subject, the author of which maintains that the Tapinocephalidae is burdened by controversy and misinformation. For instance,

“There is some disagreement over whether these animals lived in dry upland environments (Colbert), swamps, or either, depending on the species or tribe.  There is no doubt that the Tapinocephalidae occupied different ecological niches. However, the tendency of earlier writers… to consider them semi-aquatic wallowers is reminiscent of the old fable of the sauropods consigned to the swamps because their limbs were too clumsy and their bodies too heavy for them to exist on dry land.”

Such a lifestyle would seem viciously at odds with one of the more widely-accepted behavioral concepts attributed to the animals: a propensity for head-butting.

An illustration of the aforementioned hypothetical head-butting activity in Moschops.

An illustration of the aforementioned hypothetical head-butting activity in Moschops.

“The tapinocephalid skull is massively constructed, and either long-snouted (e.g. Struthiocephalus) or high and short (e.g. Moschops). Very often the top of the head is rounded, and the bones of the forehead are elevated into a sort of dome or boss, in the middle of which is a large pineal opening.  In some specimens this boss is of only moderate thickness, while in others it has become greatly thickened into a huge mass of bone (pachyostosis). It has been suggested that these animals engaged in intra-specific head-butting behavior, presumably for territory or mates. A similar thickening of the skull occurs in pachycephalosaurian (“boneheaded”) dinosaurs, and it is speculated that all of these animals practiced head-butting behavior like modern goats and bighorn sheep.”

Though I fully realize that the traditional reconstructions of head-butting pachycephalosaurids are somewhat controversial at present, I also think it’s fair to assert that the heavily built skulls of these critters were designed for something a wee bit more intense than mere sexual display.

Tapinocephalids are also well-known for their unorthodox posture: while the forelimbs splayed out to their sides in an almost lizard-like fashion, their hindlimbs were held directly beneath the hips. And finally, this post wouldn’t be complete without giving a mention to the dietary habits of Ulemosaurusand its kin. The fact that the shoulders of these animals were held significantly higher than their pelvises is indicative of a sloping, giraffe-like posture which in turn suggests that they were predominantly browsers. Some have also argued that their dentition supports the idea of omnivorous habits. Though their barrel-like chest supports the idea of a strong bias towards herbivory, the fact that “true” carnivores and herbivores are rarely found in the world of amniotes (eg: hippos will eat carrion, deer will eat baby birds and eggs, lions will eat vegetation, and crocodilians will eat fruit) encourages us to entertain the possibility of occasional animal consumption in Tapinocephalids.

May the fossil record continue to enchant us all!

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4 responses

4 09 2009
Zach Miller

Oh man, I love these critters! Thank you for profiling them–information is hard to find. And “Age of Dinosaurs…” is an excellent book. There’s a copy at the library and I’m almost positive nobody ever reads it. I should ask if I can take it off their hands. 😉

6 09 2009
tanystropheus

I can totally relate to your point about the book’s popularity in most libraries: I’m pretty sure that I’m the only person to have ever checked out the MCC copy.

8 09 2009
Brian Beatty

These are among the taxa that got me seriously interested in becoming a paleontologist as a kid and in high school. My first email address ever was synapsid@ufl.edu, because I always thought I’d run off to the Karoo and work on mammal-like reptiles, or Mesozoic mammals. Funny enough, right now I’m working on a Mesozoic mammal, though I primarily consider myself a marine mammal sort.
Thanks for posting this – Zach’s right, info on these guys is hard to find on the web, and you’re doing a great service by profiling rarely glorified taxa such as this.
Thanks,
Brian

8 09 2009
tanystropheus

I can relate, Brian! For quite a while, I was dead-set on the idea of becoming a non-mammalian synapsid specialist. However, the unfortunate fact that very few paleo programs sport professors who so much as work with them makes this a somewhat unrealistic proposition.
As for info being devilishly tricky to locate on-line, quite a bit on Permian tetrapods is available via Russian websites. But because few Western paleontologists can read the language, its largely inaccessible to those of us who live outside the country.

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