Good tidings and well-wishes!
One can easily recognize when a prehistoric creature has made its way into the public consciousness by observing how frequently vaguely similar extinct organisms are mistaken for it. Anyone who’s ever attempted to give a tour of a natural history museum or present a paleontology lecture to a high school audience is acutely aware of such a group’s propensity for identifying any large theropod as a “T. rex“, any small one as a “Velociraptor“, any hairy proboscidean as a “Woolly Mammoth”, and any extinct mammal with enlarged canines as a “Saber Toothed Cat”. To this end, it would appear that despite (or perhaps because of) its incessant misidentification as a dinosaur, the non-mammalian synapsid Dimetrodon has become one of these relatively well-known beasts in light of the fact that nearly every layman I’ve encountered proclaims that any extinct quadrupedal tetrapod with a sail is a member of the genus. However, it’s no secret that Dimetrodon certainly didn’t have a monopoly on this description, as many of its contemporaries such as Edaphosaurus and the eccentric Secodontosaurus fit the bill quite nicely as well (to say nothing of the Triassic Arizonasaurus). But perhaps the most interesting of these look-alikes wasn’t even a synapsid or amniote at all: instead, one could easily make the case that this critter was in fact the temnospondyl Platyhystrix rugosus.
The temnospondyli order was arguably the most successful group of non-amniotic terrestrial vertebrates to have ever existed and as such, was far too large and diverse to allow the constraints of this particular blog entry to boast adequate coverage of the congregation as a whole (for a nice introduction, do go here). For our purposes, we need only to concentrate upon the dissorophidae superfamily: a clade which has acquired a decent amount of attention due to its inclusion of Doleserpeton which may have been related to the ancestor modern frogs and other lissamphibians. The most obvious feature which unites this superfamily is the presence of bony plates which were either fused to the neural spines or lying just above them. Additional characteristics include long, slender limb elements and relatively large orbits (‘eye sockets’). For the full list, check out the Palaeos entry. Dissorophids made their grand debut in the late Carboniferous (aka: ‘the Pennsylvanian’ for my fellow American paleo-nerds) and persisted onwards throughout much of North America and Europe until at least the late Permian, although some authors contend that Micropholis of the early Triassic may have belonged to the group.
Right then, now that we’re taxonomically up to speed, let’s have a look at Platyhystrix itself. In his exquisite new book “The Rise Of Amphibians: 365 Million Years Of Evolution”, Robert Carroll writes:
“Isolated pieces of laterally compressed and ornamented neural spines have long been recognized from Lower Permian and even Upper Carboniferous sites in North America, but rarely with even fragments of the skull or appendicular skeleton…the most complete sequence of neural spines, showing a pattern broadly resembling the ‘sail’ of edaphosaur pelycosaurs, from the area of the atlas arch to the 15th dorsal vertebra…Subsequently, [a skull was prepared in 1981], originally collected by David Baldwin in 1881 from the lower Permian Cutler Formation in New Mexico, which showed an extremely rugose texture, closely associated with spines initially attributed to Aspidosaurus. The lateral edges of the skull table are ridged as in Broiliellus and Dissorophus. Comparable neural spines designated Astreptorhachis ohioensis, from the Upper Pennsylvanian Conemaugh Group of Ohio, support the earlier divergence of this group, near the time of emergence of the amphibamids.”
This essentially wraps up all known information about Platyhystrix as of this writing, excluding the rather amusing fact that the genus literally means ‘flat porcupine’ (also, the critter would have been approximately 1 meter long in life). However, the animal does warrant further consideration due to its role in one of the most interesting riddles paleobiology has yet to definitively solve: the enigma of ‘sail-backed’ prehistoric faunas.
(Click here to see the original post containing the above illustration)
For those significantly less nerdy than yours truly, this mystery stems from the fact that those long-extinct vertebrates which sport massive sails running down their backs are almost invariably found in either the same or nearby deposits as contemporary species with roughly the same feature. The most famous example of this is manifested by the case of Ouranosaurus and the ever-popular Spinosaurus. Although the two dinosaurs have to the best of my knowledge never been found within the same deposits, they nonetheless lived at roughly the same period of time and at similar locales (approximately 110 million years ago in Northern Africa). The situation is made more interesting, however, by the fact that the lower Permian of Texas and New Mexico has yielded not only Platyhystrix, but Dimetrodon, Edaphosaurus, and Secodontosaurus as well, all of which are easily recognized by their prominent dorsal ‘fins’. These latter beasts exhibit far more diversity, for while Spinosaurus and Ouranosaurus each have relatively broad and laterally-compressed neural spines, only those of Platyhystrix are even roughly comparable. Dimetrodon and Secodontosaurus each had fairly rod-like structures while the sail of certain Edaphosaurus species was riddled with horizontal bars. Although both groups of vertebrates are united in the fact that their respective habitats were most likely warm, wet swamps, it’s difficult to see just how this sort of environment would have produced such extravagant animals. Hopefully, additional information on these curious organisms and the ancient terrains which housed them will shed light on this most intriguing of questions.
May the fossil record continue to enchant us all!