Everything about Sphenacodontidae totally explained
The
Sphenacodontidae are a family of small to large, advanced,
carnivorous,
Late Pennsylvanian to
middle Permian pelycosaurs. 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 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 doesn't appear to have been essential for these animals. For example there's 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 isn't 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 early
therapsid. The
clade Sphenacodontia is used to designate the
monophyletic 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 the
most recent common ancestor of Sphenacodontidae and
Therapsida and all their descendants, and is defined by certain features of the skull.
Sphenacodontid fossils are so far known only from
North America and
Europe.
Further Information
Get more info on 'Sphenacodontidae'.
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