| Sphenacodontia | |
|---|---|
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| 3D restoration ofDimetrodon grandis, asphenacodontid | |
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| Restoration of a pair ofAlopecognathus angusticeps, atherocephaliantherapsid | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Synapsida |
| Clade: | Sphenacomorpha |
| Clade: | Sphenacodontia Romer &Price, 1940 |
| Subgroups | |
Sphenacodontia is astem-basedclade of derivedsynapsids. It was defined by Amson and Laurin (2011) as "the largest clade that includesHaptodus baylei,Haptodus garnettensis andSphenacodon ferox, but notEdaphosaurus pogonias".[4] They first appear during theLate Pennsylvanian (Upper Carboniferous) epoch. From the end of theCarboniferous to the end of thePermian, most of them remained large, with only some secondarily becoming small in size.
Basal Sphenacodontia constitute atransitionalevolutionary series from earlypelycosaurs to ancestraltherapsids (which in turn were the ancestors ofmore advanced forms and finally themammals). One might say that the sphenacodontians are proto-therapsids (even though there is almost a 30-million-years gap between the separation of the ancestors of therapsids from other sphenacodontians and the first appearance of therapsids in the fossil record).
Thedefining characteristics include a thickening of themaxilla visible on its internal surface, above the large front (caniniform) teeth; and thepremaxillary teeth being set in deep sockets. All other (sister group and more primitive) synapsid clades have teeth that are set in shallow sockets.
The following taxonomy follows Fröbischet al. (2011), Benson (2012) and Spinder (2016) unless otherwise noted.[3][4][5]
ClassSynapsida
Sphenacodontia in acladogram after Fröbischet al., 2011:[5]
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