Therocephalia
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| Therocephalia | |
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| Suborder: | Therocephalia
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The Therocephalia ("Beast Head") are at least as ancient as the Gorgonopsians, which they resemble, and in fact outlasted, making it through to the Early Triassic period. The earlier therocephalians were in many respects as primitive as the gorgonopsians, but they did show certain advances such as the enlargement of the temporal opening, for a lighter skull and mopre efficent muscle attachment, and reduction of the phalanges - finger and toe bones to the mammalian formula. The later therocephalians included the advanced bauriamorphs, which carried some theriodont characters to a high degree of specialization. For instance, in Bauria there was no bar of bone separating the orbit from the temporal opening; a condition typical for primitive mammals. These and other advanced features led to the long-held opinion, now rejected, that the Ictidosaurs and even some early mammals arose from a bauriamorph stem. Rather, the situation seems to be that mammalian characteristics evolved in parallel among a number of different groups. It is not surprising that several therocephalian groups, like the Lycosuchidae and the Scaleposauridae, have turned out to be artificial, the former based on skulls which retain an extra set of canines, and the latter based on mostly juvenile charcteristics.