| Stereophallodon Temporal range: Permian | |
|---|---|
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| Restoration | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Synapsida |
| Family: | † Ophiacodontidae |
| Genus: | † Stereophallodon Romer, 1937 |
| Type species | |
| Stereophallodon ciscoensis Romer, 1937 | |
Stereophallodon is an extinct genus of non-mammalian synapsids. [1]
Synapsida is one of the two major clades of vertebrate animals in the group Amniota, the other being the Sauropsida. The synapsids were the dominant land animals in the late Paleozoic and early Mesozoic, but the only group that survived into the Cenozoic are mammals. Unlike other amniotes, synapsids have a single temporal fenestra, an opening low in the skull roof behind each eye orbit, leaving a bony arch beneath each; this accounts for their name. The distinctive temporal fenestra developed about 318 million years ago during the Late Carboniferous period, when synapsids and sauropsids diverged, but was subsequently merged with the orbit in early mammals.
A therapsid is a member of the clade Therapsida, which is a major group of eupelycosaurian synapsids that includes mammals and their ancestors and close relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more underneath the body, as opposed to the sprawling posture of many reptiles and salamanders.
Ophiacodontidae is an extinct family of early synapsids from the Carboniferous and Permian. Archaeothyris, and Clepsydrops were among the earliest ophiacodontids, appearing in the Late Carboniferous. Ophiacodontids are among the most basal synapsids, an offshoot of the lineage which includes therapsids and their descendants, the mammals. The group became extinct by the Kungurian or the Roadian, replaced by anomodonts, theriodonts, and the diapsid reptiles.
Diarthrognathus is an extinct genus of tritheledontid cynodonts, known from fossil evidence found in South Africa and first described in 1958 by A.W. Crompton. The creature lived during the Early Jurassic period, about 200 million years ago. It was carnivorous and small, slightly smaller than Thrinaxodon, which was under 50 centimetres (20 in) long.
Baldwinonus is an extinct genus of basal synapsids from the Early Permian. The type species is Baldwinonus trux, named in 1940 from the Cutler Formation of New Mexico. A second species, Baldwinonus dunkardensis, was named in 1952 from Ohio. Baldwinonus was first classified in the family Eothyrididae, but the group has since been recognized as a wastebasket taxon for many early synapsids. More recently, Baldwinonus has been placed in the family Ophiacodontidae. Its phylogenetic relationship to other early synapsids remains poorly understood because it is only known from a few fragments of bone.
Calleonasus is an extinct genus of non-mammalian synapsid from the Anisian Donguz Formation of Russia.
Driveria is an extinct genus of non-mammalian synapsids the Lower Permian of San Angelo Formation, Texas. It is mostly known from several postcranial bones, including the scapula, pelvis, and a few vertebrae and ribs, although a fragment of the skull that might pertain to the upper temporal fenestra is also associated with this species.
Daptocephalus is an extinct genus of non-mammalian synapsid anomodont dicynodont, it which was found in Late Permian strata, in a biozone known precisely for the presence of fossils of this dicynodont, the Daptocephalus Assemblage Zone, in the Karoo Basin in South Africa. An additional species, D. huenei, is known from the Usili Formation in Tanzania and was formerly assigned to the genus Dicynodon before a study in 2019 recognised that the type specimen belonged to Daptocephalus.
Elatosaurus is an extinct genus of non-mammalian synapsid.
Emydorhinus is an extinct genus of non-mammalian synapsid.
Ictidostoma is an extinct genus of non-mammalian synapsids known from the Tropidostoma Assemblage Zone.
Knoxosaurus is an extinct genus of non-mammalian synapsids containing the species Knoxosaurus niteckii that existed approximately 279.5 to 268 million years ago. It was named by American paleontologist Everett C. Olson in 1962 on the basis of fragmentary fossils from Middle Permian-age deposits in the San Angelo Formation of Texas in the United States. Olson placed Knoxosaurus in a new infraorder called Eotheriodontia, which he considered a transitional group between the more reptile-like "pelycosaurs" and the more mammal-like therapsids. Knoxosaurus and Olson's other eotheriodonts were later considered to be undiagnostic remains of basal synapsids, no more closely related to therapsids than are other pelycosaur-grade synapsids.
Lanthanostegus is an extinct genus of non-mammalian synapsids from the Capitanian Tapinocephalus Assemblage Zone, Koonap Formation of South Africa. It was assigned to the clade Endothiodontia. The type and the only species is Lanthanostegus mohoii.
Milosaurus is an extinct genus of non-mammalian synapsids native to Illinois that was alive during the latest Carboniferous and earliest Permian. It was named in 1970 on the basis of FMNH 701, a partial skeleton, as well as referred material.
Orthopus is an extinct genus of non-mammalian synapsids. It is based on a partial humerus that closely resembles Estemmenosuchus, in the limited comparisons possible.
Nitosaurus is an extinct genus of non-mammalian synapsids.
Palemydops is an extinct genus of non-mammalian synapsid.
Scalopolacerta is an extinct genus of non-mammalian synapsids.
Trichasaurus is an extinct genus of caseid synapsids.
Watongia is an extinct genus of non-mammalian synapsids from Middle Permian of Oklahoma. Only one species has been described, Watongia meieri, from the Chickasha Formation. It was assigned to family Gorgonopsidae by Olson and to Eotitanosuchia by Carroll. Reisz and collaborators assigned the genus in Varanopidae. Based on comparisons of its vertebrae with other varanopids, it was the largest varanopid with a body length of approximately 2 metres. It was a contemporary of its closest relative, the much smaller Varanodon; the two may possibly represent growth stages of a single animal.
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