latest Carboniferous to Late Permian Period
lowland to upland terrestrial carnivores
Of all the pelycosaurs, the varanopseids in appearance most resemble large modern varanid (monitor) lizards. None developed the distinctive sail that distinguished many pelycosaur groups. All are of small to medium size (none more than about 1.5 meters), with slender, lightly built skulls and a slender, very typically lizard-like body, fairly slender limbs, and a long tail. In fact, we might say that the varanopseids were lizardlike in its general aspect, though this must not be taken as an indication of any close relationships with the lizards.
In the skull Varanosaurus showed certain specializations that were the beginnings of some definite evolutionary trends typical of the more advanced pelycosaurs. For instance, the skull was rather narrow, deep, and elongated, with the eyes set far back. The jaws were very long, and the teeth were numerous and sharp. There was no indication of an otic notch (to support an eardrum), and the ear was located in the vicinity of the jaw articulation.
All varanopseids have specialized marginal dentition, and flattened curved teeth with anterior and posterior cutting edges. The skull, as mentioned above, is light, the temporal fenestra being enlarged and the lower jaw slender. The postcranial skeleton is also lightly built, giving varanopseids a sleek appearance, superficially similar to modern monitor lizards. The varanopseids were probably the most agile predators of their time. These successful animals outlasted all other carnivorous pelycosaurs as highly specialized lizard-like insectvores and small carnivores, and survived as late as the early late Permian (Capitanian epoch). The last forms were all small, and in the end they were probably outcompeted by the even more lizard-like Younginiforme diapsids
Varanopseids retain several primitive skull and skeletal features that indicate they are more primitive than other Pelycosaurs apart from the Eothyridids. For this reason modern cladistic paleontogists reject the opinions of earlier workers like Romer and Price (1940) who associated varanopseids with the advanced sphenacodontid family, and even suggested that Varanops, may have been closed to the ancestry of sphenacodontids. The most recent hypothesis places varanopseids within the Eupelycosauria, as its most primitive member, and close to the ancestral linneage from which the more advanced ophiacodontids, edaphosaurs, and sphenacodontids evolved.
Unfortunately the evidence of the fossil record contradicts this hypothesis. All of the really early pelycosaurs belong to the supposedly advanced ophiacodontid family. Rather then erect numerous "ghost lineages" to fill in the gaps, I would suggest instead that the Varanopseids, like the Eothyridids represent a secondarily primitive lineage that had lost certain specialised features. It is likely that both these groups evolved from Ophaicodontids during the great drought of the Kasimovian epoch, when the long period of aridity proved favourable to the reptiles, and not so good for the big amphibians of the coal swamps. No doubt future discoveries will no doubt determine which theory is the correct one.
|Technical Diagnosis of this family|
Varanopseidae - list of genera
Mycterosaurus longiceps is the most primitive member of the family. This small pelycosaur has the typical varanopseid features, but lacks several characteristics of the advanced members of this family.
Varanosaurus was a contemporary of Ophiacodon , and probably competed with it for fish in the same swamps. Its skull was also deep and narrow, the jaws somewhat elongated and armed with small, spiky teeth. It had the build of a modern monitor lizard, but lacked the specialisations of the typical varanopseids
The larger varanopseids, Varanops, Aerosaurus, and Varanodon (above) are all characterized by certain common characteristics of the skull, and are obviously closely related. Varanodon is also one of the youngest known pelycosaurs,
|some Links and References|
Biology 356 - Major Features of Vertebrate Evolution - Permo-Carboniferous Synapsids - by Dr. Robert Reisz, University of Toronto
Varanopseidae - Palaeos - Vertebrates - Toby White's excellent technical summary, lots of links. Also incorporates material from these pages
Romer, A.S. and Price, L.I. Review of the Pelycosauria, Geological Society of America Special Papers,. no.28,
Robert R. Reisz, Pelycosauria, Encylopedia of Paleoherpetology, Part 17A, 1986, Gustav Fischer Verlag, Stuttgart and New York
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