Ophiacodontidae is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

of early eupelycosaurs from the

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 ''Carboniferou ...

and

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleo ...

. '' Archaeothyris'', and ''

Clepsydrops ''Clepsydrops'' is an extinct genus of primitive synapsids from the early Late Carboniferous that was related to ''Archaeothyris''. The name means 'hour-glass appearance' (Greek ''klepsydra'' = "hourglass" + Greek ''ops'' = "eye, face, appearan ...

'' were among the earliest ophiacodontids, appearing in the

Late Carboniferous Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effe ...

. Ophiacodontids are among the most basal synapsids, an offshoot of the lineage which includes

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 mo ...

and their descendants, the

mammals 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 o ...

. The group became extinct by the

Middle Permian 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 Texas, and dates between 272.95 ± ...

, replaced by

anomodont Anomodontia is an extinct group of non-mammalian therapsids from the Permian and Triassic periods. By far the most speciose group are the dicynodonts, a clade of beaked, tusked herbivores.Chinsamy-Turan, A. (2011) ''Forerunners of Mammals: Ra ...

theriodonts The theriodonts ( clade Theriodontia) are a major group of therapsids which appeared during the Middle Permian and which includes the gorgonopsians and the eutheriodonts, itself including the therocephalians and the cynodonts. Naming In 1876, Ric ...

, and the

diapsid Diapsids ("two arches") are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The group first appeared about three hundred million years a ...

reptiles.

Characteristics

The lifestyle of ophiacodonts has long been controversial. Some studies suggested that they were semi-aquatic, and some even suggested a fairly aquatic lifestyle, but a recent study based on a quantitative inference model suggested that both ''

'' and '' Ophiacodon'' were terrestrial. Vertebral morphometric data also support, though ambiguously, a rather terrestrial lifestyle for '' Ophiacodon'', which could reach a length of .The Macmillan Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals
/ref> '' Archaeothyris'' may also have been terrestrial, but no detailed study of its habitat has been performed so far. The earliest ophiacodontids resembled

varanids The Varanidae are a family of lizards in the superfamily Varanoidea within the Anguimorpha group. The family, a group of carnivorous and frugivorous lizards, includes the living genus '' Varanus'' and a number of extinct genera more closely rela ...

in body proportions, while others were larger with elongated skulls and massive shoulder girdles, probably to provide muscle attachment to support the weight of the large head.

Classification

Traditionally, '' Archaeothyris'', '' Ophiacodon'', '' Varanosaurus'' and the briefly described ''

Baldwinonus ''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 ...

'', ''

'', '' Echinerpeton'', ''

Stereophallodon ''Stereophallodon'' is an extinct genus of non-mammalian synapsids. See also * List of pelycosaurs This list of pelycosaurs is an attempt to create a comprehensive listing of all genera that have ever been included in the synapsida excluding th ...

'' and '' Stereorhachis'' are included in the Ophiacodontidae. '' Protoclepsydrops'' was also regarded as ophiacodontid, however there is debate as to whether or not it was a

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 reptil ...

. ''Echinerpeton'' and ''Sterophallodon'' were included for the first time in a phylogenetic analysis by Benson (2012). '' Echinerpeton'' was found to be a wildcard taxon due to its small amount of known materials. It occupies three possible positions, falling either as the most basal synapsid, as the sister taxon of

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 insec ...

plus more derived taxa, or as an ophiacodontid more derived than ''Archaeothyris''. Below is a

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 ...

modified from the analysis of Benson (2012), after the exclusion of ''Echinerpeton'':

References

External links

Ophiacodontidae
- at Palaeos Pennsylvanian first appearances Cisuralian extinctions Prehistoric synapsid families Taxa named by Franz Nopcsa von Felső-Szilvás {{paleo-synapsid-stub