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Gorgodon
''Gorgodon'' is an extinct genus of basal synapsid. The genus is monotypic, known only from the type species ''Gorgodon minutus'' from the Early Permian of the southwestern United States. The only known remains of ''Gorgodon'' are two fossils consisting of fragments of the skull. ''Gorgodon'' was described and named by paleontologist Everett C. Olson in 1962 from the San Angelo Formation in Knox County, Texas. Based on what is known of ''Gorgodon'' — the squamosal, quadrate, and pterygoid bones of the back of the skull, the maxilla and premaxilla bones that make up the front of the skull, and several teeth — ''Gorgodon'' had a relatively large temporal fenestra and a pair large, conical caniniform teeth at the front of the jaw. Other distinguishing features of ''Gorgodon'' include the fused connection between the quadrate and squamosal bones and a long transverse process of the pterygoid (a projection extending from the pterygoid bone on the underside of the skull).
Olson classified ''Gorgodon'' as a very early therapsid because it had a heterodont dentition and large temporal fenestra not seen in the most basal synapsids but present in therapsids. He placed it in the family Phthinosuchidae because its teeth seemed similar to those of ''Phthinosaurus'', an enigmatic therapsid from the Middle Permian of Russia that is most likely a dinocephalian. However, the only known teeth of ''Phthinosaurus'' are from its lower jaw and the known teeth of ''Gorgodon'' are from its upper jaw. Olson reasoned that the shape of the teeth of ''Gorgodon'' match what would be expected for the upper teeth of ''Phthinosaurus'' even though there are no homologous features between the two taxa that would support such a relationship. Olson thought that ''Gorgodon'' was more primitive than ''Phthinosaurus'', and that both were ancestors of a group of therapsids called gorgonopsids.
Sidor and Hopson (1995) proposed that ''Gorgodon'' and several other early therapsids that Olson described from the San Angelo Formation were instead the crushed remains of sphenacodontids. Sphenacodontids are a group of non-therapsid synapsids that were common in what is now the southwestern United States during the Early Permian. Although ''Gorgodon'' is most likely a non-therapsid synapsid, its relationship to other synapsids has not been assessed due to its lack of distinguishing anatomical features.
==References==
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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