Wednesday Wonders: Estemmenosuchus

27 05 2009

Good tidings and well-wishes!

“If you can’t tell what it was used for, attribute it to sexual display”. This is one of the underlying principles of paleontology. When presented with a fossilized beast which sports a bizarre appendage or other osteological anomaly that seems incomparable to any modern creature, most paleontologists will claim that it was utilized for the purposes of procreative attraction. As with any trend, this can certainly go too far, such as arguing that pachycephalosaurids employed their notoriously thick skulls exclusively to catching the eye of a passing female. However, in some cases, it seems quite appropriate. It’s also of great importance to note that many of these features likely served multiple functions. A grand example of this may be found in the famed Parasaurolophus, whose iconic head crest likely worked towards cooling the brain in addition to producing an eerie, horn-like resonating sound.

Given this tendency, it should come as no surprise that when asked to discuss the theoretical function of Estemmenosuchus sp., most paleontologists simply state “sexual display”.

Estemmenosuchus skull.

Estemmenosuchus skull.

 In the compendium “The Age Of Dinosaurs In Mongolia And Russia” (the title of which is fairly ironic considering the fact that Estemmenosuchus and its kin lived from the middle to late Permian in present-day Russia), Bernard Battail and  Mikhail Surkov give the following diagnosis regarding the strange headgear of this massive and highly unorthodox skull:

“Anterior [frontal] parts of nasals forming unpaired boss on dorsal [upper] surface of snout;postorbitals and postfrontals forming pair of short outgrowths; jugal and squamosal forming very massive lateral [facing the side] outgrowth” 

But perhaps what’s even more interesting about this creature (scientifically speaking) are its teeth. When one wishes to recreate the life and times of an extinct vertebrate, few remains prove to be remotely as useful as its teeth. Teeth can determine a creature’s dietary preferences and thus can offer enormous clues regarding its environment and phylogeny (the latter particularly applies to mammals which literally have thousands of tooth varieties). In his recent book “Your Inner Fish: A Journey Into The 3.5-Billion-Year History Of The Human Body” (which I’d highly reccomend to anyone with even the faintest interest in evolution and/or paleontology), Neil Shubin writes “The French anatomist Georges Cuvier once famously boasted that he could reconstruct an animal’s entire skeleton from a single tooth. This is a little over the top, but the general point is valid; teeth are a powerful window into an animal’s lifestyle”.

Allright, enough beating around the bush…back to the animal in question. So what do Estemmenosuchus‘ teeth tell us?

Estemmenosuchus skull profile

Estemmenosuchus skull profile

The creature’s incisors are rather long and curved while the postcanine teeth are noticably small. However, most readers will have had their attention primarily drawn to the beastie’s short, thick canines. Here we have a bit of a dilemma: while the canines suggest a carnivorous preference, the reduction and volume of the postcanines indicate strong herbivorous tendencies. (Several teeth are also visible on the animal’s palate, which are namely vomer, palatine, and pterygoid in nature) 

However, the question of to which fodder the creature was biased is put to rest when one examines Estemmenosuchus‘ bulky body and barrel-like chest, which indicate that the animal was investing a large amount of time digesting plants. Thus, it would appear that the comparatively large anterior teeth gathered the vegetation whilst their posterior brethren kept it within the mouth (the creature likely did little to no chewing). Nonetheless, the Palaeos article on the genera (by the way, if you’re a hard-core paleo-nerd and don’t consult Palaeos on a regular basis, you need to start doing so ASAP, especially if Permian and Triassic critters tickle your fancy) argues that “These animals would nevertheless have taken carrion when they could find it, as the great force exerted by the chisel-like front teeth could cut up meat quite easily”.

So to recap, here we have a large, cumbersome-looking, barrel-chested animal with dentition capable of processing both meat and vegetable matter and a body which suggests a strong morphological prejudice towards the latter. Other than that, the creature is known primarily from channel flood deposits, which suggests a semi-aquatic lifestyle or at least a niche in close association to bodies of water. Hmm, what sort of modern analogue could one come up with?…

This analogy is fairly widespread, as many authors have compared Estemmenosuchusto a Permian hippo, resulting in reconstructions like the following courtesy of Wikipedia (I couldn’t locate the artist’s name):

 While the functional morphology of Estemmenosuchus is indeed fascinating, it’s high time for some taxonomy which, in this animal’s case, is both intriguing and controversial.

Estemmenosuchusis the name-giving genus of the family Estemmenosuchidae, which is distinguished by the presence of teeth on vomers and a pachyostosed skull. In addition to the two known species of Estemmenosuchus known to science (E. uralensis, andE. mirabilis), the genera Molybdopygus, Anoplosuchus and Zopherosuchushave also been atributed to this group (for more information on these beasts, see the link to the Palaeos article I posted earlier). These creatures were members of the Therapsidaorder, which includes mammals. Most Permian workers also place the Estemmenosuchidae within the Dinocephalia suborder, however, according to Battail and Surkov:

“Recently, Ivakhneko has expressed the view that the Estemmenosuchidae should be excluded from the Dinocephalia and brought together with the Eotitanosuchidae.”

Additionally, those authors who continue to place the Estemmenosuchidae within the Dinocephalia often disagree about the family’s specific place within the suborder. Some have suggested that its members bear a striking resemblance to Styracocephalus (go herefor more information about this genus). However, as the aforementioned Palaeos entry points out:

“Connections [to the Estemmenosuchidae] are sometimes suggested with Styracocephalus, but in the estemmenosuchids the ‘horns’ are situated on the frontals and directed dorsally. In Styracocephalus the ‘horns’ are formed by the tabularand directed posteriorly. Otherwise their features very similar to those of Styracocephalus. It is not possible to say therefore whether the relationship is one of ancestor- descendent or simply evolutionary convergence due to similar lifestyle, although difference in the bones forming the horns would suggest the latter”.

Regardless of its taxonomic placement, Estemmenosuchus is but one of a host of fascinating yet strangely understudied non-mammalian synapsid genera of the Permian. Hopefully, further research will unveil more about these amazing beasts in the future.

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5 responses

27 05 2009
Zach Miller

Ah, an old favorite of mine. Wonderful post! I wonder about the joint flexibility of Estemmenosuchus‘ jaw–could it grind its food somehow? Straight chewing is out, given the weak postcanine teeth. However, Edaphosaurus developed an interesting grinding mechanism: it developed tooth plates on the palatte and along the inner sides of the mandible, and used its tongue to move plant material across the grinding surface and shred it up.

I wonder if Estemmenosuchus did the same thing?

28 05 2009
tanystropheus

It’s possible…Estemmenosuchus did have several teeth on its palate, though I’m unaware of any on the mandible. Judging from everything I’ve read on the animal, it looks like any sort of traditional mastication is out as you’ve noted. I suspect that it may have relied heavily on gastroliths to this end, though probably not to the extent of sauropods.

I’d never read about this mechanism in Edaphosaurus of which you speak, though it seems quite efficient. Is there any way to test for the presence of such a heavy-duty tongue to do the job?

28 05 2009
Zach Miller

Robust hyoid bones would do the trick, but hyoids are ridiculously rare given their relative lightness and the fact that they don’t articulate with anything–they are held in place by soft tissue alone, so they’d be the first to go in a streambed or lake.

What’s more, the hyoid apparatus is made up of three main bones, and THEY are held together by cartilage.

But hyoids anchor the tongue (in most animals) and support the soft tissue of the lower jaw. They also provide some support for the trachea (I think). The bigger the tongue, the more robust the hyoids.

4 09 2009
Weekly Wonders: Ulemosaurus « The Theatrical Tanystropheus

[…] 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 (which I’ll […]

31 03 2010
Weekly Spotlight: Varanops « The Theatrical Tanystropheus

[…] stretch of time boasts some of the most diverse and unique critters known to science, including the heavily ornamented Estemmenosuchus, the mysterious Ophiacodon, and the eccentric little […]

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