Sphenacodontidae
| Sphenacodontidae Temporal range: Pennsylvanian - Guadalupian, 300–272 Ma |
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| Dimetrodon limbatus skeleton | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Sphenacodontoidea |
| Family: |
†Sphenacodontidae Marsh, 1878 |
| Genera & Clade | |
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Ctenorhachis |
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Ctenorhachis
Cutleria
Macromerion
Neosaurus
Secodontosaurus
? Steppesaurus
Sphenacodontinae
Sphenacodontidae (Greek: "wedge point tooth family") is an extinct family of small to large, advanced, carnivorous, Late Pennsylvanian to middle Permian pelycosaurs. Primitive forms were generally small (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. Sphenacodontid fossils are so far known only from North America and Europe.
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 tooth", although all members of the family have this attribute).
Several large (~3 meters) and advanced members of this group (Ctenospondylus, Sphenacodon, Secodontosaurus and Dimetrodon) are distinguished by a tall sail along the back, made up of elongated vertebral neural spines, 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 from New Mexico) lacks a sail, while a very similar and closely related genus (Dimetrodon – fossils known from Texas) has one. During the Permian, 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.
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Wikipedia