- Sphenacodontidae
Taxobox
name = Sphenacodontidae
fossil_range = LatestCarboniferous - MiddlePermian
image_width = 250px
image_caption = "Palaeohatteria ".
regnum =Animal ia
phylum = Chordata
classis =Synapsid a
ordo =Pelycosaur ia
unranked_familia =Eupelycosauria
familia = Sphenacodontidae
familia_authority = Marsh,1878
subdivision_ranks = Genera & Clade
subdivision = "Ctenorhachis "
"Sphenacodontinae"
*"Ctenospondylus "
*"Dimetrodon "
*"Neosaurus "
*"Secodontosaurus "
*"Sphenacodon "
*"Steppesaurus "The Sphenacodontidae are a family of small to large, advanced, carnivorous,
Late Pennsylvanian to middle Permianpelycosaur s. Primitive forms ("Haptodus ", etc) were generally small in size (60 cm to 1 meter), but during the later part of the early Permian these animals grew progressively larger (up to 3 meters or more), to become the top predators of their environments.The skull is long, deep and narrow, an adaptation for strong jaw muscles. The front teeth are large and dagger-like, whereas the teeth in the sides and rear of the jaw are much smaller. (hence the name of the well-known genus "
Dimetrodon " - "two-measure teeth", although all members of the family have this attribute).Several large (c. 3 meters) and advanced members of this group ("
Secodontosaurus ", "Ctenospondylus ", "Dimetrodon ") are distinguished by a tall sail along the back, made up of elongatedvertebra lneural spine s, which in life must have been covered with skin and blood vessels, and presumably functioned as a thermoregulatory device. However, possession of a sail does not appear to have been essential for these animals. For example there is the case in which one genus ("Sphenacodon " - fossils known fromNew Mexico ) lacks a sail, while a very similar and closely related genus ("Dimetrodon " - fossils known fromTexas ) has one. During thePermian , these two regions were separated by a narrow sea-way, but it is not clear why one geographically isolated group should evolve a sail, but the other group not.The family Sphenacodontidae is actually paraphyletic as originally described, defined by shared primitive synapsid characters; these animals constitute an evolutionary gradation from primitive
synapsid to earlytherapsid . Theclade Sphenacodontia is used to designate themonophyletic group that includes Sphenacodontids and all their descendants (including mammals), while Sphenacodontidae in the strict sense includes only specialised pelycosaurs, and not earlier more primitive members of the family like "Haptodus", "Palaeohatteria", "Pantelosaurus", and "Cutleria" (in pre-cladistic classifications all included under the genus "Haptodus"). The clade Sphenacodontoidea is used by Laurin and Reisz 1997 to designate themost recent common ancestor of Sphenacodontidae andTherapsida and all their descendants, and is defined by certain features of the skull. Sphenacodontid fossils are so far known only fromNorth America andEurope .See also
*
Evolution of mammals
*haptodus 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, [http://tolweb.org/accessory/Synapsid_Classification_&_Apomorphies?acc_id=466 Autapomorphies of the main clades of synapsids]
* Reisz, R. R., 1986, "Handbuch der Paläoherpetologie – Encyclopedia of Paleoherpetology, Part 17A Pelycosauria" Verlag Dr. Friedrich Pfeil, ISBN 3-89937-032-5
* 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 American Special Papers, No 28External links
* [http://www.palaeos.com/Vertebrates/Units/Unit390/400.html Synapsida: Sphenacodontia]
* [http://www.fmnh.helsinki.fi/users/haaramo/Metazoa/ Deuterostoma/Chordata/Synapsida/Pelycosauria/Sphenacodontidae.htm Sphenacodontidae] - list of species
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