Synapsids—not to be confused with therapsids, which are a subordinate group to synapsids—are a group of animals that includes mammals and every animal more closely related to mammals than to the other members of the amniotes clade, such as reptiles and birds. They are easily separated from other amniotes by having a temporal fenestra, an opening low in the skull roof behind each eye, leaving a bony arch beneath each; this accounts for their name. Primitive synapsids are usually called pelycosaurs or pelycosaur-grade synapsids. This informal term consists of all synapsids that are not therapsids, a monophyletic more advanced mammal-like group. The non-mammalian synapsids were described as mammal-like reptiles in classical systematics, but this misleading terminology is no longer in use as synapsids as a whole are no longer considered reptiles. They are now more correctly referred to as stem mammals or proto-mammals. Synapsids evolved from basal amniotes and are one of the two major groups of amniotes, the other being the sauropsids, the group that includes reptiles and birds. The distinctive temporal fenestra developed in the ancestral synapsid about 312 million years ago, during the Late Carboniferous period.
Therapsida is a group of eupelycosaurian synapsids that includes mammals and their ancestors. 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. The earliest fossil attributed to Therapsida is Tetraceratops insignis from the Lower Permian.
Dinocephalia is a clade of large-bodied early therapsids that flourished for a brief time in the Middle Permian between 270 and 260 million years ago (Ma), but became extinct, leaving no descendants. Dinocephalians included herbivorous, carnivorous, and omnivorous forms. Many species had thickened skulls with many knobs and bony projections. Dinocephalian fossils are known from Russia, China, Brazil, South Africa, Zimbabwe, and Tanzania.
The Guadalupian is the second and middle series/epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and date between 272.3 ± 0.5 – 259.8 ± 0.4 Mya. The series saw the rise of the therapsids, a minor extinction event called Olson’s Extinction and a significant mass extinction called the end-Capitanian extinction event.
The Eupelycosauria originally referred to a suborder of 'pelycosaurs', but has been redefined to designate a clade of synapsids that includes most pelycosaurs, as well as all therapsids and mammals. They first appear during the Early Pennsylvanian epoch, and represent just one of the many stages in the acquiring of mammal-like characteristics, in contrast to their earlier amniote ancestors. The defining characteristics which separate these animals from the Caseasauria are based on details of proportion of certain bones of the skull. These include a long, narrow supratemporal bone, and a frontal bone with a wider connection to the upper margin of the orbit.
Biarmosuchia is an extinct clade of non-mammalian synapsids from the Permian. Biarmosuchians are the most basal group of the therapsids. They were moderately-sized, lightly-built carnivores, intermediate in form between basal sphenacodont "pelycosaurs" and more advanced therapsids. Biarmosuchians were rare components of Permian ecosystems, and the majority of species belong to the clade Burnetiamorpha, which are characterized by elaborate cranial ornamentation.
Tetraceratops insignis is an extinct synapsid from the Early Permian of Texas. It was originally classified as an early and very primitive member of Therapsida, a group that includes mammals and their close extinct relatives. However, it is now seen as a primitive non-therapsid sphenacodont rather than a genuine basal therapsid.
Dicynodon is a type of dicynodont therapsid that flourished during the Upper Permian period. Like all dicynodonts, it was herbivorous. This animal was toothless, except for prominent tusks, hence the name. It probably cropped vegetation with a horny beak, much like a tortoise, while the tusks may have been used for digging up roots and tubers.
Dinogorgon is a genus of gorgonopsid from the Late Permian of South Africa and Tanzania. The generic name Dinogorgon is derived from Greek, meaning "terrible gorgon", while its species name rubidgei is taken from the surname of renowned Karoo paleontologist, Professor Bruce Rubidge, who has contributed to much of the research conducted on therapsids of the Karoo Basin. The type species of the genus is D. rubidgei.
Rubidgea atrox is a genus of gorgonopsid from the upper Permian of South Africa and Tanzania. The generic name Rubidgea is taken from the surname of renowned Karoo paleontologist, Professor Bruce Rubidge, who has contributed to much of the research conducted on therapsids of the Karoo Basin. Its species name atrox is derived from Latin, meaning “fierce, savage, terrible”. Rubidgea is part of the gorgonopsian subfamily Rubidgeinae, a derived group of large-bodied gorgonopsians restricted to the Late Permian (Lopingian). The subfamily Rubidgeinae first appeared in the Tropidostoma Assemblage Zone. They reached their highest diversity in the Cistecephalus and Daptocephalus assemblage zones of the Beaufort Group in South Africa.
Theriognathus is an extinct genus of therocephalian therapsid belonging to the family Whaitsiidae, from South Africa and Tanzania. Theriognathus has been dated as existing during the Late Permian. Although Theriognathus means mammal jaw, the lower jaw is actually made up of several bones as seen in modern reptiles, in contrast to mammals. Theriognathus displayed many different reptilian and mammalian characteristics. For example, Theriognathus had canine teeth like mammals, and a secondary palate, multiple bones in the mandible, and a typical reptilian jaw joint, all characteristics of reptiles. It is speculated that Theriognathus was either carnivorous or omnivorous based on its teeth, and was suited to hunting small prey in undergrowth. This synapsid adopted a sleek profile of a mammalian predator, with a narrow snout and around 1 meter long. Theriognathus is represented by 56 specimens in the fossil record.
Burnetia is an extinct genus of biarmosuchian therapsids in the family Burnetiidae, from the Late Permian of South Africa. Burnetia is known so far from a single holotype skull lacking the lower jaws described by South African paleontologist Robert Broom in 1923. Due to erosion and dorsoventral crushing, features of the skull are hard to interpret. Stutural lines are further distorted by the unusual shape of the skull roof, including many bosses and protuberances.
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 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.
Tetragonias is an extinct genus of non-mammalian synapsid from the Anisian Manda Beds of Tanzania. Tetra- means “four,” and goni- means “angle,” referencing the square shape of the Tetragonias skull when viewed dorsally. Not to be confused with Tetragonia,Tetragonias were dicynodont anomodonts discovered in the late 1960s by paleontologist A. R. I. Cruickshank in the Manda Formation.
Raranimus is an extinct genus of therapsids of the Middle Permian. It was described in 2009 from a partial skull found in 1998 from the Dashankou locality of the Xidagou Formation, outcropping in the Qilian Mountains of Gansu, China. The genus is the most basal known member of the clade Therapsida, to which the later Mammalia belong.
The Neotherapsida are a clade of therapsids. The clade includes anomodonts and the more derived theriodonts, which include mammals.
Ruhuhucerberus is an extinct genus of very large, extinct gorgonopsian therapsids which existed in Tanzania during the Late Permian. Its fossils are found in the Penman Kawinga Formation of the Ruhuhu Basin. It existed sympatrically with the even larger Rubidgea.
Elph is an extinct genus of dicynodont therapsids from Russia. Four specimens have been found from the Sokolki Assemblage in European Russia, representing a fauna that dates back to the Late Permian. Elph was a small herbivore that lived alongside carnivorous akidnognathids and inostranceviids, as well as larger herbivores like Dicynodon and pareiasaurids. The type species E. borealis was named in 1999. Elph has a short snout and tusks and is closely related to Interpresosaurus and Katumbia.
The Usili Formation is a Late Permian geologic formation in Tanzania. It preserves fossils of many terrestrial vertebrates from the Permian, including temnospondyls, pareiasaurs, therapsids and the archosauromorph Aenigmastropheus.
Lende is an extinct genus of biarmosuchian from Malawi. It contains one species, Lende chiweta, first reported by Jacobs and colleagues in 2005 and is a burnetiamorph – a group of biarmosuchians characterized by numerous bosses and swellings on the skull. The type specimen was discovered in the early 90s in the Permian Lower Bone Bed (B1) of the Chiweta Beds of Malawi, which are believed to correlate with the Cistecephalus Assemblage Zone of the South African Karoo Supergroup, the Usili Formation of Tanzania, and the Upper Madumabisa Mudstone Formation of Zambia. The holotype of the genus Lende is MAL 290, which comprises an almost complete skull and lower jaw.
