Eutherocephalia ("true beast head") is an extinct

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

of advanced

therocephalia Therocephalia is an extinct suborder of eutheriodont therapsids (mammals and their close relatives) from the Permian and Triassic. The therocephalians ("beast-heads") are named after their large skulls, which, along with the structure of their te ...

therapsid 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 ...

s. Eutherocephalians are distinguished from the lycosuchids and

scylacosaurids Scylacosauridae is an extinct family of therocephalian therapsids. Scylacosaurids lived during the Permian period and were among the most basal therocephalians. The family was named by South African paleontologist Robert Broom in 1903. Scylacosa ...

, two early therocephalian families. While lycosuchids and scyalosaurids became extinct by the end of the

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 Paleoz ...

period, eutherocephalians survived the

Permian–Triassic extinction event The Permian–Triassic (P–T, P–Tr) extinction event, also known as the Latest Permian extinction event, the End-Permian Extinction and colloquially as the Great Dying, formed the boundary between the Permian and Triassic geologic periods, as ...

. The group eventually became extinct in the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided in chronostratigraphy. The Middle Triassic spans the time between Ma and ...

Characteristics

The Eutherocephalians evolved several mammal-like traits through

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...

with Cynodontia. Among those traits were the loss of palatine teeth and the reduction of the

parietal eye A parietal eye, also known as a third eye or pineal eye, is a part of the epithalamus present in some vertebrates. The eye is located at the top of the head, is photoreceptive and is associated with the pineal gland, regulating circadian rhythm ...

. The latter organ is instrumental in

thermoregulation Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature ...

among lizards and

snakes Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more joi ...

, indicating both eutherocephalians and cynodonts were evolving toward a more active,

homeothermic Homeothermy, homothermy or homoiothermy is thermoregulation that maintains a stable internal body temperature regardless of external influence. This internal body temperature is often, though not necessarily, higher than the immediate environmen ...

lifestyle, though the eye never fully disappeared in the eutherocephalians.

Classification

The

Eutherocephalia contains the majority of therocephalians, yet the

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

relations of the groups within it remain unclear. Eutherocephalia is supported as a true clade in many phylogenetic analyses, but the placement of groups like

Akidnognathidae Akidnognathidae is an extinct family of therocephalian therapsids from the Late Permian and Early Triassic of South Africa, Russia and China. The family includes many large-bodied therocephalians that were probably carnivorous, including ''Mosch ...

Hofmeyriidae Hofmeyriidae is a family of therocephalian therapsids. It includes the genus '' Ictidostoma''. References External links Hofmeyriidaein the Paleobiology Database The Paleobiology Database is an online resource for information on the distrib ...

, Whaitsiidae, and

Baurioidea Baurioidea is a superfamily of therocephalian therapsids. It includes advanced therocephalians such as ''Regisaurus'' and ''Bauria''. The superfamily was named by South African paleontologist Robert Broom in 1911. Bauriamorpha, named by D. M. ...

, all of which lie within Eutherocephalia, remains debated.

References

Permian first appearances Middle Triassic extinctions Animal infraorders {{paleo-therapsid-stub