These lists of synapsids collectively include every genus that has ever been included in the clade Synapsida- the mammals and their evolutionary precursors. The lists includes accepted genera along with those now considered invalid, doubtful ( nomina dubia ), not formally published ( nomina nuda ), junior synonyms of more established names, as well as genera that are no longer considered synapsids.
 | This article includes a species-related list of lists. |
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. 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.
Sauropsida is a taxonomic clade that consists of reptiles, birds, and the extinct Parareptilia. All living sauropsids are members of the subgroup Diapsida, the Parareptilia having died out 200 million years ago. The term originated in 1864 with Thomas Henry Huxley, who grouped birds with reptiles based on fossil evidence. Sauropsids are the sister taxon to synapsids, some of which later evolved into mammals.
Dimetrodon is an extinct genus of synapsids that lived during the Cisuralian, around 295–272 million years ago (Ma). It is a member of the family Sphenacodontidae. The most prominent feature of Dimetrodon is the large neural spine sail on its back formed by elongated spines extending from the vertebrae. It walked on four legs 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 coming from a geological deposit called the Red Beds of Texas and Oklahoma. More recently, fossils have been found in Germany. Over a dozen species have been named since the genus was first described in 1878.
The pelycosaurs were previously considered an order, but are now only an informal grouping composed of basal or primitive Late Paleozoic synapsids, sometimes called "mammal-like reptiles". They consist of all synapsids excluding the therapsids and their descendants.
Sphenacodontidae is an extinct family of small to large, advanced, carnivorous, Late Pennsylvanian to middle Permian pelycosaurs. 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 their environments. Sphenacodontid fossils are so far known only from North America and Europe.
Sphenacodontia is a stem-based clade of derived synapsids. It was defined by Amson and Laurin (2011) as "the largest clade that includes Haptodus baylei, Haptodus garnettensis and Sphenacodon ferox, but not Edaphosaurus pogonias". They first appear during the Late Pennsylvanian epoch.
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.
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, potentially aquatic Caseidae. These two groups share a number of specialised features associated with the morphology of the snout and external naris.
Therocephalia is an extinct suborder of eutheriodont therapsids from the Permian and Triassic. The therocephalians ("beast-heads") are named after their large skulls, which, along with the structure of their teeth, suggest that they were carnivores. Like other non-mammalian synapsids, therocephalians were once described as "mammal-like reptiles". Therocephalia is the group most closely related to the cynodonts, which gave rise to the mammals. This relationship takes evidence in a variety of skeletal features. The phylogeny of therocephalians has been disputed, as the monophyly of the group and the relationships of its members are unclear.
Varanopidae is an extinct family of amniotes that resembled monitor lizards and might have had the same lifestyle, hence their name. Typically, they are considered synapsids that evolved from an Archaeothyris-like synapsid in the Late Carboniferous, but a recent study has recovered them as diapsid reptiles. A varanopid from the latest Middle Permian Pristerognathus Assemblage Zone is the youngest known varanopid and the last member of the "pelycosaur" group of synapsids.
Ophiacodontidae is an extinct family of early eupelycosaurs 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 Middle Permian, replaced by anomodonts, theriodonts, and the diapsid reptiles.
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.
Sphenacodontoidea is a node-based clade that is defined to include the most recent common ancestor of the Sphenacodontidae and the Therapsida and their descendants. They are defined according to a number of specialised characteristics concerning proportions of the bones of the skull and the teeth.
Tetraceratops insignis is an extinct synapsid from the Early Permian that may be the first known representative of Therapsida, a group that includes mammals and their close extinct relatives. It is known from a single 90-millimetre-long (3.5 in) skull, discovered in Texas in 1908.
Clepsydrops is an extinct genus of primitive synapsids from the early Late Carboniferous that was related to Archaeothyris. The name means 'hour-glass appearance'.
James Allen Hopson is an American paleontologist and professor at the University of Chicago. His work has focused on the evolution of the synapsids, and has been focused on the transition from basal synapsids to mammals, from the late Paleozoic through the Mesozoic Eras. He received his doctorate at Chicago in 1965, and worked at Yale before returning to Chicago in 1967 as a faculty member in Anatomy, and has also been a research associate at the Field Museum of Natural History since 1971. He has also worked on the paleobiology of dinosaurs, and his work, along with that of Peter Dodson, has become a foundation piece for the modern understanding of duckbill crests, social behavior, and variation.
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).
Ianthodon is an extinct genus of basal sphenacodont synapsids from the Late Carboniferous about 306-303 million years ago. The taxon was discovered and named by Kissel & Reisz in 2004. The only species in the taxon, Ianthodon schultzei, was found by separating it from a block that also contained the remains of Petrolacosaurus and Haptodus. The evolutionary significance of the taxon wasn't realized until a publication in 2015. The fossil of this organism was discovered in Garnett, Kansas.
