Eupelycosauria is a large clade of animals characterized by the unique shape of their

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...

, encompassing all

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

s and their closest extinct relatives. They first appeared 308million years ago during the Early Pennsylvanian epoch, with the fossils of ''

Echinerpeton ''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'' ...

'' and perhaps an even earlier genus, ''

Protoclepsydrops ''Protoclepsydrops'' is an extinct genus of early synapsids, found in Joggins, Nova Scotia. The name means 'first ''Clepsydrops, and refers to it being the predecessor of the other early synapsid '' Clepsydrops''. Description Like ''Archaeothyri ...

'', representing just one of the many stages in the evolution of mammals,Kemp. T.S., 1982, ''Mammal-like Reptiles and the Origin of Mammals''.

Academic Press Academic Press (AP) is an academic book publisher founded in 1941. It was acquired by Harcourt, Brace & World in 1969. Reed Elsevier bought Harcourt in 2000, and Academic Press is now an imprint of Elsevier. Academic Press publishes referen ...

, New York in contrast to their earlier

amniote Amniotes are a clade of tetrapod vertebrates that comprises sauropsids (including all reptiles and birds, and extinct parareptiles and non-avian dinosaurs) and synapsids (including pelycosaurs and therapsids such as mammals). They are distin ...

ancestors. Eupelycosaurs are

synapsid Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes repti ...

s, animals whose skull has a single opening behind the eye. They are distinguished from the

Caseasauria 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 insect ...

n synapsids by having a long, narrow

supratemporal bone The supratemporal bone is a paired cranial bone present in many tetrapods and tetrapodomorph fish. It is part of the temporal region (the portion of the skull roof behind the eyes), usually lying medial (inwards) relative to the squamosal and later ...

(instead of one that is as wide as it is long) and a

frontal bone The frontal bone is a bone in the human skull. The bone consists of two portions.''Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, part ...

with a wider connection to the upper margin of the

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a ...

. Laurin, M. and Reisz, R. R., 1997
Autapomorphies of the main clades of synapsids
-

Tree of Life Web Project The Tree of Life Web Project is an Internet project providing information about the diversity and phylogeny of life on Earth. This collaborative peer reviewed project began in 1995, and is written by biologists from around the world. The site h ...

The only living descendants of basal eupelycosaurs are the

s. The group was originally considered a suborder of pelycosaurs or "mammal like reptiles",Reisz, R. R., 1986, ''Handbuch der Paläoherpetologie – Encyclopedia of Paleoherpetology, Part 17A Pelycosauria'' Verlag Dr. Friedrich Pfeil, but it was redefined in 1997, and the term pelycosaur itself has fallen into disfavor. We now know that the eupelycosaurs were not in fact reptiles nor of reptile lineage - the modern term

stem mammal Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes reptil ...

is used instead. Some recent studies suggested that one of its subgroups,

Varanopidae 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 Carbonifero ...

, are really nested within

sauropsids Sauropsida ("lizard faces") is a clade of amniotes, broadly equivalent to the class Reptilia. Sauropsida is the sister taxon to Synapsida, the other clade of amniotes which includes mammals as its only modern representatives. Although early sy ...

, leaving the other defined subgroup of it, Metopophora, as its synonym.

Evolution

Many non-therapsid eupelycosaurs were the dominant land animals from the latest

Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carboniferous ...

to the end of the

Early Permian 01 or '01 may refer to: * The year 2001, or any year ending with 01 * The month of January * 1 (number) Music * 01'' (Richard Müller album), 2001 * ''01'' (Son of Dave album), 2000 * ''01'' (Urban Zakapa album), 2011 * ''O1'' (Hiroyuki Sawano ...

epoch. Ophiacodontids were common from their appearance in the late

( Pennsylvanian) to the early Permian, but they became progressively smaller as the early Permian progressed. The edaphosaurids, along with the caseids, were the dominant

herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthp ...

s in the early part of the Permian. The most renowned edaphosaurid is '' Edaphosaurus'', a large [] herbivore which had a sail on its back, probably used for thermoregulation and mating. Sphenacodontidae, Sphenacodontids, a family of carnivorous eupelycosaurs, included the famous ''Dimetrodon'', which is sometimes mistaken for a

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is ...

, and was the largest predator of the period. Like ''Edaphosaurus'', ''Dimetrodon'' also had a distinctive sail on its back, and it probably served the same purpose - regulating heat. The

varanopid 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 Carbonifero ...

family passingly resembled today's

monitor lizard Monitor lizards are lizards in the genus ''Varanus,'' the only extant genus in the family Varanidae. They are native to Africa, Asia, and Oceania, and one species is also found in the Americas as an invasive species. About 80 species are recogn ...

s and may have had the same lifestyle.Paleos Synapsida

Therapsids Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...

descended from a clade closely related to the sphenacodontids. They became the succeeding dominant land animals for the rest of the Permian, and in the latter part of the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

, descendants of the

cynodont The cynodonts () ( clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide variet ...

s, an advanced group of therapsids, gave rise to the first true

s. All non-therapsid synapsids, including all basal eupelycosaurs, as well as many other life forms, became extinct at the end of Permian period.

Classification

The following

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

follows the one found o
Mikko's Phylogeny Archive

References

External links

{{Taxonbar, from=Q1349838 Tetrapod unranked clades Extant Pennsylvanian first appearances