Eutherocephalia ("true beast head") is an extinct

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

advanced The Advanced Party (), otherwise known as the Advanced Association () was a liberal and centrist Zionist political association in Mandatory Palestine founded by several urban liberal Zionists. The party was founded in order to represent the voice ...

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

n therapsids. Eutherocephalians are distinguished from the lycosuchids and

scylacosaurids Scylacosauridae is an extinct family (biology), family of therocephalian therapsids. Scylacosaurids lived during the Permian period and were among the most basal (phylogenetics), basal therocephalians. The family was named by South African paleon ...

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

Permian The Permian ( ) is a geologic period and System (stratigraphy), 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 251.902 Mya. It is the s ...

period, eutherocephalians survived the

Permian–Triassic extinction event The Permian–Triassic extinction event (also known as the P–T extinction event, the Late Permian extinction event, the Latest Permian extinction event, the End-Permian extinction event, and colloquially as the Great Dying,) was an extinction ...

. The group eventually became extinct in the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epoch (geology), epochs of the Triassic period (geology), period or the middle of three series (stratigraphy), series in which the Triassic system (stratigraphy), system is di ...

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 comm ...

with

Cynodontia Cynodontia () is a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Mammals are cynodonts, as are their extinct ances ...

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

parietal eye A parietal eye (third eye, pineal eye) is a part of the epithalamus in some vertebrates. The eye is at the top of the head; is photoreceptive; and is associated with the pineal gland, which regulates circadian rhythmicity and hormone production ...

. 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 vertebrate, limbless reptiles of the suborder Serpentes (). Cladistically Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in overlapping Scale (zoology), scales much like other members of ...

, 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 envir ...

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

Classification

The

Eutherocephalia contains the majority of therocephalians, yet the

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

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 '' Mos ...

, Hofmeyriidae,

Whaitsiidae Whaitsiidae is an extinct family (biology), family of therocephalian therapsids. References

Whaitsiidae, Permian first appearances Permian extinctions Prehistoric therapsid families {{paleo-therapsid-stub ...

, 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 {{paleo-therapsid-stub