Synapsids are one of the two major clades of vertebrate animals in the group Amniota, the other being the sauropsids, which include reptiles and birds. The synapsids were once the dominant land animals in the late Paleozoic and early Mesozoic, but the only extant group that survived into the Cenozoic are the 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.
Dimetrodon is a genus of non-mammalian synapsid that lived during the Cisuralian age of the Early Permian period, around 295–272 million years ago. It is a member of the family Sphenacodontidae. With most species measuring 1.7–4.6 m (5.6–15.1 ft) long and weighing 28–250 kg (62–551 lb), the most prominent feature of Dimetrodon is the large neural spine sail on its back formed by elongated spines extending from the vertebrae. It was an obligate quadruped and had a tall, curved skull with large teeth of different sizes set along the jaws. Most fossils have been found in the Southwestern United States, the majority of these coming from a geological deposit called the Red Beds of Texas and Oklahoma. More recently, its fossils have also been found in Germany and over a dozen species have been named since the genus was first erected in 1878.
Sphenacodontidae is an extinct family of sphenacodontoid synapsids. Small to large, advanced, carnivorous, Late Pennsylvanian to middle Permian "pelycosaurs". The most recent one, Dimetrodon angelensis, is from the late Kungurian or early Roadian San Angelo Formation. However, given the notorious incompleteness of the fossil record, a recent study concluded that the Sphenacodontidae may have become extinct as recently as the early Capitanian. Primitive forms were generally small, but during the later part of the early Permian these animals grew progressively larger, to become the top predators of terrestrial environments. Sphenacodontid fossils are so far known only from North America and Europe.
Petrolacosaurus is an extinct genus of diapsid reptile from the late Carboniferous period. It was a small, 40-centimetre (16 in) long reptile, and one of the earliest known reptile with two temporal fenestrae. This means that it was at the base of Diapsida, the largest and most successful radiation of reptiles that would eventually include all modern reptile groups, as well as dinosaurs and other famous extinct reptiles such as plesiosaurs, ichthyosaurs, and pterosaurs. However, Petrolacosaurus itself was part of Araeoscelida, a short-lived early branch of the diapsid family tree which went extinct in the mid-Permian.
Caseasauria is one of the two main clades of early synapsids, the other being the Eupelycosauria. Caseasaurs are currently known only from the Late Carboniferous and the Permian, and include two superficially different families, the small insectivorous or carnivorous Eothyrididae, and the large, herbivorous Caseidae. These two groups share a number of specialised features associated with the morphology of the snout and external naris.
Eothyrididae is an extinct family of very primitive, insectivorous synapsids. Only three genera are known, Eothyris, Vaughnictis and Oedaleops, all from the early Permian of North America. Their main distinguishing feature is the large caniniform tooth in front of the maxilla.
Ctenospondylus is an extinct genus of sphenacodontid synapsid
Sphenacodon is an extinct genus of synapsid that lived from about 300 to about 280 million years ago (Ma) during the Late Carboniferous and Early Permian periods. Like the closely related Dimetrodon, Sphenacodon was a carnivorous member of the Eupelycosauria family Sphenacodontidae. However, Sphenacodon had a low crest along its back, formed from blade-like bones on its vertebrae instead of the tall dorsal sail found in Dimetrodon. Fossils of Sphenacodon are known from New Mexico and the Utah–Arizona border region in North America.
Secodontosaurus is an extinct genus of "pelycosaur" synapsids that lived from between about 285 to 272 million years ago during the Early Permian. Like the well known Dimetrodon, Secodontosaurus is a carnivorous member of the Eupelycosauria family Sphenacodontidae and has a similar tall dorsal sail. However, its skull is long, low, and narrow, with slender jaws that have teeth that are very similar in size and shape—unlike the shorter, deep skull of Dimetrodon, which has large, prominent canine-like teeth in front and smaller slicing teeth further back in its jaws. Its unusual long, narrow jaws suggest that Secodontosaurus may have been specialized for catching fish or for hunting prey that lived or hid in burrows or crevices. Although no complete skeletons are currently known, Secodontosaurus likely ranged from about 2 to 2.7 metres (7–9 ft) in length, weighing up to 110 kilograms (250 lb).
Mycterosaurus is an extinct genus of synapsids belonging to the family Varanopidae. It is classified in the varanopid subfamily Mycterosaurinae. Mycterosaurus is the most primitive member of its family, existing from 290.1 to 272.5 MYA, known to Texas and Oklahoma. It lacks some features that its advanced relatives have.
Casea is a genus of herbivorous caseid synapsids that lived during the late Lower Permian (Kungurian) in what is now Texas, United States. The genus is only represented by its type species, Casea broilii, named by Samuel Wendell Williston in 1910. The species is represented by a skull associated with a skeleton, a second skull, a partial skull with a better preserved dentition than that of the preceding skulls, and several incomplete postcranial skeletons. Three other Casea species were later erected, but these are considered today to be invalid or belonging to different genera. Casea was a small animal with a length of about 1.20 m and a weight of around 20 kg.
Oedaleops is an extinct genus of caseasaur synapsids from the Early Permian of the southwestern United States. Fossils have been found in the Cutler Formation in New Mexico, which dates back to the Wolfcampian stage of the Early Permian. All remains belong to the single known species Oedaleops campi. Oedaleops was closely related to Eothyris, and both are part of the family Eothyrididae. Like Eothyris, it was probably an insectivore.
Aerosaurus is an extinct genus within Varanopidae, a family of non-mammalian synapsids. It lived between 252-299 million years ago during the Early Permian in North America. The name comes from Latin aes (aeris) “copper” and Greek sauros “lizard,” for El Cobre Canyon in northern New Mexico, where the type fossil was found and the site of former copper mines. Aerosaurus was a small to medium-bodied carnivorous synapsid characterized by its recurved teeth, triangular lateral temporal fenestra, and extended teeth row. Two species are recognized: A. greenleeorum (1937) and A. wellesi (1981).
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.
Biseridens is an extinct genus of anomodont therapsid, and one of the most basal anomodont genera known. Originally known from a partial skull misidentified as an eotitanosuchian in 1997, another well-preserved skull was found in the Qingtoushan Formation in the Qilian Mountains of Gansu, China, in 2009 that clarified its relationships to anomodonts, such as the dicynodonts.
Echinerpeton is an extinct genus of synapsid, including the single species Echinerpeton intermedium from the Late Carboniferous of Nova Scotia, Canada. The name means 'spiny lizard' (Greek). Along with its contemporary Archaeothyris, Echinerpeton is the oldest known synapsid, having lived around 308 million years ago. It is known from six small, fragmentary fossils, which were found in an outcrop of the Morien Group near the town of Florence. The most complete specimen preserves articulated vertebrae with high neural spines, indicating that Echinerpeton was a sail-backed synapsid like the better known Dimetrodon, Sphenacodon, and Edaphosaurus. However, the relationship of Echinerpeton to these other forms is unclear, and its phylogenetic placement among basal synapsids remains uncertain.
Mesenosaurus is an extinct genus of amniote. It belongs to the family Varanopidae. This genus includes two species: the type species Mesenosaurus romeri from the middle Permian Mezen River Basin of northern Russia, and Mesenosaurus efremovi from the early Permian (Artinskian) Richards Spur locality. M. romeri’s stratigraphic range is the middle to late Guadalupian while M. efremovi’s stratigraphic range is the Cisuralian.
Euromycter is an extinct genus of caseid synapsids that lived in what is now southern France during the Early Permian about 285 million years ago. The holotype and only known specimen of Euromycter (MNHN.F.MCL-2) includes the complete skull with lower jaws and hyoid apparatus, six cervical vertebrae with proatlas, anterior part of interclavicle, partial right clavicle, right posterior coracoid, distal head of right humerus, left and right radius, left and right ulna, and complete left manus. It was collected by D. Sigogneau-Russell and D. Russell in 1970 at the top of the M1 Member, Grès Rouge Group, near the village of Valady, Rodez Basin. It was first assigned to the species "Casea" rutena by Sigogneau-Russell and Russell in 1974. More recently, it was reassigned to its own genus, Euromycter, by Robert R. Reisz, Hillary C. Maddin, Jörg Fröbisch and Jocelyn Falconnet in 2011. The preserved part of the skeleton suggests a size between 1,70 m (5,5 ft) and 1,80 m (5,9 ft) in length for this individual.
Abdalodon is an extinct genus of late Permian cynodonts, known by its only species A. diastematicus.Abdalodon together with the genus Charassognathus, form the clade Charassognathidae. This clade represents the earliest known cynodonts, and is the first known radiation of Permian cynodonts.
