Sphenacodontidae
Encyclopedia
Sphenacodontidae is a family of small to large, advanced, carnivorous
, Late Pennsylvanian to middle Permian pelycosaur
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 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.
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
.
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
, Late Pennsylvanian to middle Permian pelycosaur
Pelycosaur
The pelycosaurs are an informal grouping composed of basal or primitive Late Paleozoic synapsid amniotes. Some species were quite large and could grow up to 3 meters or more, although most species were much smaller...
s. Primitive forms (Haptodus
Haptodus
Haptodus was a small sphenacodont, a clade that includes therapsids and hence, mammals. It was at least in length. It lived from Latest Carboniferous to Early Permian, in the equatorial Pangea. It was a medium-sized predator, feeding on insects and small vertebrates. It is one of the basalmost...
, 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
Apex predator
Apex predators are predators that have no predators of their own, residing at the top of their food chain. Zoologists define predation as the killing and consumption of another organism...
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
Dimetrodon
Dimetrodon was a predatory synapsid genus that flourished during the Permian period, living between 280–265 million years ago ....
- "two-measure tooth", although all members of the family have this attribute).
Several large (~3 meters) and advanced members of this group (Ctenospondylus
Ctenospondylus
Ctenospondylus, was a pelycosaur that was about 3 meters long. It lived from Latest Carboniferous to Early Permian. Its fossils were found in the U.S. states of Ohio and Texas. It was a carnivore and preyed upon animals close to its size...
, Sphenacodon
Sphenacodon
Sphenacodon was a pelycosaur that was about in length. Sphenacodon belongs to the family Sphenacodontidae, a lineage that was related to the therapsids...
, Secodontosaurus
Secodontosaurus
Secodontosaurus was a pelycosaur that lived in Texas during the Early Permian age. Though it had the same body style as other sphenacodontids, it had an unusually low and narrow skull. It had a long neural spines, like Dimetrodon, which Secodontosaurus was related to...
and Dimetrodon
Dimetrodon
Dimetrodon was a predatory synapsid genus that flourished during the Permian period, living between 280–265 million years ago ....
) 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
Thermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
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
Sphenacodon
Sphenacodon was a pelycosaur that was about in length. Sphenacodon belongs to the family Sphenacodontidae, a lineage that was related to the therapsids...
- fossils known from New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
) lacks a sail, while a very similar and closely related genus (Dimetrodon
Dimetrodon
Dimetrodon was a predatory synapsid genus that flourished during the Permian period, living between 280–265 million years ago ....
- fossils known from Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
) has one. During the Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "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.
The family Sphenacodontidae is actually paraphyletic as originally described, defined by shared primitive synapsid characters; these animals constitute an evolutionary gradation from primitive synapsid
Synapsid
Synapsids are a group of animals that includes mammals and everything more closely related to mammals than to other living amniotes. They are easily separated from other amniotes by having an opening low in the skull roof behind each eye, leaving a bony arch beneath each, accounting for their name...
to early therapsid. The clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
Sphenacodontia
Sphenacodontia
Sphenacodontia is the name given to the clade that includes the Sphenacodontidae and all their descendants . They first appear during the Late Pennsylvanian epoch. The defining characteristics include a thickening of the maxilla visible on its internal surface, above the large front teeth; and...
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
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
classifications all included under the genus Haptodus). The clade Sphenacodontoidea is used by Laurin and Reisz 1997 to designate the most recent common ancestor
Most recent common ancestor
In genetics, the most recent common ancestor of any set of organisms is the most recent individual from which all organisms in the group are directly descended...
of Sphenacodontidae and Therapsida
Therapsida
Therapsida is a group of the most advanced synapsids, and include the ancestors of mammals. Many of the traits today seen as unique to mammals had their origin within early therapsids, including hair, lactation, and an erect posture. The earliest fossil attributed to Therapsida is believed to be...
and all their descendants, and is defined by certain features of the skull.
Sphenacodontid fossils are so far known only from North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
and Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
.