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This list of pelycosaurs is an attempt to create a comprehensive listing of all genera that have ever been included in the synapsida excluding therapsida and purely vernacular terms. The list includes all commonly accepted genera, but also genera that are now considered invalid, doubtful ( nomina dubia ), or were not formally published ( nomina nuda ), as well as junior synonyms of more established names, and genera that are no longer considered pelycosaurs.
The list currently contains 83 generic names.
Naming conventions and terminology follow the International Code of Zoological Nomenclature. Technical terms used include:
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Introduction
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.
Pelycosaur is an older term for basal or primitive Late Paleozoic synapsids, excluding the therapsids and their descendants. Previously, the term mammal-like reptile had been used, and pelycosaur was considered an order, but this is now thought to be incorrect, and seen as outdated.
Sphenacodontidae is an extinct family of 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 their environments. Sphenacodontid fossils are so far known only from North America and Europe.
Eupelycosauria is a large clade of animals characterized by the unique shape of their skull, encompassing all mammals and their closest extinct relatives. They first appeared 308 million years ago during the Early Pennsylvanian epoch, with the fossils of Echinerpeton and perhaps an even earlier genus, Protoclepsydrops, representing just one of the many stages in the evolution of mammals, in contrast to their earlier amniote ancestors.
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.
Varanopidae is an extinct family of amniotes that resembled monitor lizards and may have filled a similar niche, hence the name. Typically, they are considered synapsids that evolved from an Archaeothyris-like synapsid in the Late Carboniferous. However, some recent studies have recovered them being taxonomically closer to 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.
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.
Varanops is an extinct genus of Early Permian varanopid synapsids known from Texas and Oklahoma of the United States. It was first named by Samuel Wendell Williston in 1911 as a second species of Varanosaurus, Varanosaurus brevirostris. In 1914, Samuel W. Williston reassigned it to its own genus and the type species is Varanops brevirostris.
Varanodon is an extinct genus of amniotes from the family Varanopidae. It has been found in the Chickasha Formation of Oklahoma, which dates to the Roadian stage of the Middle Permian. The largest varanopid known at the time of its description, with a skull length of 17.5 centimetres (6.9 in), it was closely related to and lived alongside its much larger relative Watongia. The two may represent growth stages of a single animal.
Colobomycter is an extinct genus of lanthanosuchoid parareptile known from the Early Permian of Oklahoma.
Elliotsmithia is a small varanopid synapsid found from the late Middle Permian of South Africa. It is the sole basal synapsid "pelycosaur" known from the supercontinent Gondwana and only two specimens have been yielded to date. Its species name longiceps is derived from Latin, meaning "long head". Both known Elliotsmithia fossils were recovered from Abrahamskraal Formation rocks—within the boundaries of the Tapinocephalus Assemblage Zone—of the lower Beaufort Group. It was named for the late Sir Grafton Elliot Smith in 1937.
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.
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.
Acleistorhinus (ah-kles-toe-RYE-nuss) is an extinct genus of parareptile known from the Early Permian of Oklahoma. It is notable for being the earliest known anapsid reptile yet discovered. The morphology of the lower temporal fenestra of the skull of Acleistorhinus bears a superficial resemblance to that seen in early synapsids, a result of convergent evolution. Only a single species, A. pteroticus, is known, and it is classified in the Family Acleistorhinidae, along with Colobomycter.
Ianthodon is an extinct genus of basal haptodontiform synapsids from the Late Carboniferous about 304 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.
Heleosaurus scholtzi is an extinct species of basal synapsids, known as pelycosaurs, in the family of Varanopidae during the middle Permian. At first H. scholtzi was mistakenly classified as a diapsid. Members of this family were carnivorous and had dermal armor, and somewhat resembled monitor lizards. This family was the most geologically long lived, widespread, and diverse group of early amniotes. To date only two fossils have been found in the rocks of South Africa. One of these fossils is an aggregation of five individuals.
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 Qingtoushan 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.
Richards Spur is a Permian fossil locality located at the Dolese Brothers Limestone Quarry north of Lawton, Oklahoma. The locality preserves clay and mudstone fissure fills of a karst system eroded out of Ordovician limestone and dolomite, with the infilling dating to the Artinskian stage of the early Permian (Cisuralian), around 289 to 286 million years ago. Fossils of terrestrial animals are abundant and well-preserved, representing one of the most diverse Paleozoic tetrapod communities known. A common historical name for the site is Fort Sill, in reference to the nearby military base. Fossils were first reported at the quarry by workers in 1932, spurring a wave of collecting by local and international geologists. Early taxa of interest included the abundant reptile Captorhinus and microsaurs such as Cardiocephalus and Euryodus. Later notable discoveries include Doleserpeton, the most diverse assortment of parareptiles in the Early Permian, and the rare early diapsid Orovenator.
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