of Sphenacodontidae and Therapsida and all their descendants, and is defined by certain features of the skull. See also Evolution of mammals References Carroll, R. L. (1988), Vertebrate Paleontology and Evolution, WH Freeman & Co. Colbert, E. H., (1969), Evolution of the Vertebrates, John Wiley & Sons Inc (2nd ed.) Laurin, M. and Reisz, R. R., 1997, Autapomorphies of the main clades of synapsids Reisz, R. R., 1986, Handbuch der Paläoherpetologie – Encyclopedia of Paleoherpetology, Part 17A Pelycosauria Verlag Dr. Friedrich Pfeil, Romer, A. S., (1947, revised ed. 1966) Vertebrate Paleontology, University of Chicago Press, Chicago Romer, A. S. and Price, L. I., (1940), Review of the Pelycosauria, Geological Society of America Special Papers, No 28 External links Synapsida: Sphenacodontia Deuterostoma/Chordata/Synapsida/Pelycosauria/Sphenacodontidae.htm Sphenacodontidae - list of species Prehistoric synapsid families Pennsylvanian first appearances Guadalupian extinctions Taxa named by Othniel Charles Marsh