late Carboniferous to Early Permian Period
lowland terrestrial/semi-aquatic pscivores and carnivores
Ophiacodontids include small to very large carnivorous pelycosaurs distinguished by certain specialised cranial features. These were possibly semi-aquatic or fully aquatic animals, appearing early in the Carboniferous coal swamps.
There is a curious tendency to increase in the skull to trunk ratio, larger taxa having unusually large, awkward looking, elongate skulls. These animals also have relatively large, massive shoulder girdles, possibly to provide muscle attachment to support the weight of the huge head.
The modern cladistic paradigm unites ophiacodontids, edaphosaurids, and sphenacodontids by the possession of certain specialised features of the skull. However this is also the oldest family of pelycosaurs, and indeed of Synapsids/Theropsids, with the oldest known pelycosaurs - Protoclepsydrops and Archaeothyris - being included in this family (the former tentatively, the latter definitely).
From an ophiacodont stem pelycosaurs evolved in two directions. One line of pelycosaurian development led to large aggressive, land-living carnivores, the sphenacodontids, the other to large plant -eating forms, the edaphosaurs. The ophaicodonts and edaphosaurs died out with the drying out of their swamp and pond-margin environments during the middle Permian, the sphenacodontids continued on a bit longer.
|Technical Diagnosis of this family|
Ophiacodontidae - genus list
Protoclepsydrops from the Middle Pennsylvanian of Joggins, Nova Scotia has been placed within the Ophiacodontidae, but its identity and taxonomic status is uncertain, partly because the known skeletal remains are fragmentary .
Archaeothyris, from slightly younger sediments near Florence, Nova Scotia, is the oldest known diagnosable ophiacodontid. This was a more advanced animal than the contempporary protorhyridid captorhinomorphs. Its jaws were strong, and could be opened wide and snapped shut. Although its teeth were all the same shape - sharp and pointed - they were of different sizes, including a large pair of canines at the front of the jaws. Such teeth suggest a varied, carnivorous diet, and area distinguishing mark of the carnivorous pelycosaurs.
Ophiacodon, a large Permian reptile commonly 1.5 to 2.5 meters in length, was a specialised member of the Ophaicodontid lineage. It is also the best known member of the family, represented by an extensive fossil record in North America, that has been subdivided, somewhat arbitrarily (based largely on stratigraphic position and size) into six species. The skull was very deep, with long jaws, these being provided with many sharp teeth. It has often been suggested that Ophiacodon was a fish-eating reptile that lived largely along the shores of streams and ponds, although the high narrow skull would seem to mitigate against such a lifestyle.
|some Links and References|
Biology 356 - Major Features of Vertebrate Evolution - Permo-Carboniferous Synapsids - by Dr. Robert Reisz, University of Toronto
Ophiacodontidae - Palaeos - incorporating Toby White's Vertebrate Notes and 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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