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Temporal range: Pennsylvanian-Recent, 299.9–0 Ma
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Eupelycosauria
Clade: Sphenacodontia
Genera and Clades

Sphenacodontia is a stem-based clade of derived synapsids. It was defined by Amson and Laurin (2011) as "the largest clade that includes Haptodus baylei, Haptodus garnettensis and Sphenacodon ferox, but not Edaphosaurus pogonias".[1] They first appear during the Late Pennsylvanian epoch.

Basal Sphenacodontia constitute a transitional evolutionary series from early pelycosaurs to ancestral therapsids (which in turn were the ancestors of more advanced forms and finally the mammals). One might say that the Sphenacodontians are proto-therapsids.


The defining characteristics include a thickening of the maxilla visible on its internal surface, above the large front (caniniform) teeth; and the premaxillary teeth being set in deep sockets. All other (sister group and more primitive) synapsid clades have teeth that are set in shallow sockets.


Haptodus, from Latest Carboniferous to Early Permian
Secodontosaurus, Early Permian

The following taxonomy follows Fröbisch et al. (2011) and Benson (in press) unless otherwise noted.[1][2]

Class Synapsida

See also[edit]


  1. ^ a b Benson, R.J. (2012). "Interrelationships of basal synapsids: cranial and postcranial morphological partitions suggest different topologies". Journal of Systematic Palaeontology. in press. doi:10.1080/14772019.2011.631042. 
  2. ^ Jörg Fröbisch, Rainer R. Schoch, Johannes Müller, Thomas Schindler and Dieter Schweiss (2011). "A new basal sphenacodontid synapsid from the Late Carboniferous of the Saar-Nahe Basin, Germany" (PDF). Acta Palaeontologica Polonica. 56 (1): 113–120. doi:10.4202/app.2010.0039. 

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