Week Of Wonders: Ophiacodon

18 12 2009

Good tidings and well-wishes!

Longtime readers of ‘The Theatrical Tanystropheus‘ may have observed my general tendency to ignore non-avian dinosaurs within its confines. This trend is largely due to the simple fact that nearly every lay person with whom I become engaged in a discussion concerning paleontology seems to be utterly convinced that the subject should simply be re-named ‘dinosaur-ology’ to disambiguate its intended purpose. In other words, the average person seems to think that either paleo is concerned only with the 165-million year reign of the dinosauria (to the exclusion of their descendants of course) or, worse, that anything which becomes extinct is automatically classified as a ‘dinosaur’ by the scientific community (Zach Miller of ‘When Pigs Fly Returns’ recently created a post through which those of us in the blogosphere can vent our frustrations with this latter aggravating phenomenon).

However, at this time, I feel that it’s necessary to remind everyone precisely whose responsibility it is to remedy this regrettable situation: those of us currently taking residence in the paleontological community. If we cannot bring our own academic fields into the public consciousness, who can?

Since this rant has already taken up too much space, I’ll descend from my soap box and redirect those interested to this exquisite diagnosis of the problem from both perspectives in order to move on to the subject at hand.

Virtually no prehistoric organism of any era is more commonly mistaken for a dinosaur than the infamous Dimetrodon , even though the animal is quite demonstrably more closely akin to us than it is to any ‘terrible lizard’ (which is actually a mis-translation. Check this out!). However, I’d like to dedicate this particular post to an early relative of the famed beastie which was somewhat less showy (though just as interesting) and accordingly receives far less attention from the popular media and scientific community alike: Ophiacodon sp. of the early Permian.

Ophiacodon reconstruction

Ophiacodon was a moderately large (species ranged from 2 to nearly 4 meters in length) pelycosaurs, a wonderfully diverse group of non-mammalian synapsids hailing from the Carboniferous and (mostly) early Permian (though some species held out until the second half of the latter period). The pelycosauria order was among the first group of amniotes to evolve, paving the way for virtually every organism most of us instantly picture when we hear the word ‘animal’, including ourselves.

A trio of Pelycosaurs: Cotylorhynchus in the background, Ophiacodon in the midground, and Varanops in the foreground.

However, most of the scientific community recognizes them for pioneering another characteristic: the ‘synapsid skull’. According to the invaluable ‘palaeos.com’ entry on the pelycosauria:

“[The cranium] features a single, large opening on the side of the skull (the temporal region) behind the orbit (eye socket). This special opening allowed the development of larger and longer jaw muscles, and hence stronger jaws that could be opened wider and closed forcefully, enabling the animal to dispatch struggling or larger prey. It was this simple evolutionary adaptation that gave the pelycosaurs the edge in the struggle for survival. All that was needed was a prolonged period of drought, such as the sudden period of aridity during the Kasimovian Period, to kill off many of the large stem tetrapods that kept the pelycosaurs insignificant, and these creatures were able to emerge as the dominant life-form on Earth during the Permian period, while the captorhinids remained small and relatively insignificant.”

An Ophiacodon skull which exhibits the traits mentioned in the previous paragraph.

Ophiacodon itself was more specifically the name-giving genus of the Ophiacodontidae family, a group from whence the sphenacodontids and edaphosaurids would later emerge. The most obvious traits uniting the family’s members are their disproportionally-large elongate skulls and massively wide shoulder girdles (the latter was almost certainly utilized to help support the former). Their awkward proportions and cone-like teeth have traditionally led most scientists to believe that these were semiaquatic piscivores, however, this interpretation is likely a definitive example of being wrong and right simultaneously.

A collection of Ophiacodon teeth.

Fairly complete Ophiacodon skeletons have revealed that the creature’s wrists and ankles were weakly attatched to their respective limbs, suggesting that the animal’s legs were largely incapable of equipping it with an efficient means of terrestrial locomotion. This fact throws additional weight to the idea of Ophiacodon being an obligate fish-eater, but precisely how the beast captured its scaly prey (fun fact: skin impressions of Ophiacodon and its relatives reveal that these animals were scale-less throughout much of their bodies but nevertheless sported dermal scutes on their bellies)  remains highly debatable.

Ophiacodon skeletal mount.

Many Permian workers have maintained that Ophiacodon may have swung its skull from side to side through a body of water while pursuing fish. However, one huge factor obstructs this view: the skull itself. As the 181st entry of the Carnegie Institute Of Washington’s Publication pointed out in 1913,

“the skull [of Ophiacodon] is remarkably narrow, high, and long. The very small nares [(‘nasal openings’)] are at the extreme front end, the small orbits are far posterior [(‘very far behind them’)]. The upper side is flattened in the frontal and parietal region: it’s greatest width is just behind the orbits… Immdeiately in front of the orbits the upper surface narrows; thence to the nares the border, formed chiefly by the nasals, is gently convex in outline. Doubtless in life the very broad sides of the face were gently convex, but, as preserved, the thin bones forming them are nearly in contact, producing a light concavity between the thickened alveolar border of the maxilla and the thickened nasal border; the bones of this region are scarcely thicker than writing paper for the most part…”

Ophiacodon skull replica in aerial view.

This most certainly is not the skull of an animal which actively pursues fish by laterally swinging its skull as the aforementioned Permian paleontologists have argued because if it’s utilized in this fashion, an immense amount of drag will hinder its progress (try striking a fast moving fish underwater with the broad side of an oar and you’ll see what I mean).

A fishing Ophiacodon reconstruction.

So just how did Ophiacodon and its kin use their bizarre skulls? Recently, the paleontology department of the Houston Museum of Natural Science has put forth the following idea for Dimetrodon’s dietary habits: the creature may have used its massive size to tackle large and cumbersome freshwater sharks (such as Xenacanthus) with whom it shared its semi-aquatic environment. Though Dimetrodon was much more heavily-built than any ophiacodont, this scenario provides an intriguing hypothetical answer to one of the fundamental questions about these latter animals which has plagued the scientific community for several decades.

May the fossil record continue to enchant us all!




2 responses

31 03 2010
Weekly Spotlight: Varanops « The Theatrical Tanystropheus

[…] diverse and unique critters known to science, including the heavily ornamented Estemmenosuchus, the mysterious Ophiacodon, and the eccentric little […]

20 08 2010

my friend looks like the fat dino with the short neck… he’s a real winna

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