Gorgonopsia

Gorgonopsians

Temporal range: Middle Permian-Late Permian, 265–252 Ma

PreꞒ

Ꞓ

O

S

D

C

P

T

J

K

Pg

N

Skeleton of Inostrancevia alexandri at the Museo delle Scienze, Trento, Italy

Scientific classification

Kingdom:

Animalia

Phylum:

Chordata

Clade:

Therapsida

Clade:

Neotherapsida

Clade:

Theriodontia

Seeley, 1895

Clade:

†Gorgonopsia

Lydekker, 1890

Genera

List[show]

Gorgonopsia (from the Ancient Greek γοργών, meaning "gorgon", and ὄψ, meaning "aspect") is an extinct clade of early sabre-toothed therapsids from the Middle to Upper Permian. They are characterised by a long and narrow skull, as well as engorged upper and sometimes lower canine teeth and incisors which were likely used as slashing and stabbing weapons. Postcanine teeth are generally reduced or absent. For hunting large prey, they possibly used a bite-and-retreat tactic, ambushing and taking a debilitating bite out of the target, and following it at a safe distance before its injuries exhaust it, whereupon the gorgonopsian would grapple the animal and deliver a killing bite. They would have had an incredible gape, possibly in excess of 90°, without having to unhinge the jaw.

They markedly increased in size as time went on, growing from small skull lengths of 10–15 cm (4–6 in) in the Middle Permian to bear-like proportions of up to 60 cm (2 ft) in the Upper Permian. The latest gorgonopsians, Rubidgeinae, were the most robust of the group and could produce especially powerful bites. They are thought to have been completely terrestrial and could walk with a semi-erect gait, with a similar terrestrial locomotory range as modern crocodilians. They may have been more agile than their prey items, but were probably inertial homeotherms rather than endotherms as contemporary therocephalians and cynodonts, and thus were probably comparatively less active. Though gorgonopsians were able to maintain a rather high body temperature, it is unclear if they would have also had fur, sweat glands, or whiskers. They had an overall more reptilian than mammalian brain. Most species may have been predominantly diurnal, active during the day, though some could have been crepuscularor nocturnal. They are thought to have had binocular vision, a parietal eye, a keen sense of smell, a functional vomeronasal organ ("Jacobson's organ"), and possibly a rudimentary eardrum.

The major therapsid groups had all evolved by 265 million years ago from a 'pelycosaur' ancestor (a poorly defined group including all synapsids which are not therapsids). The therapsid takeover from pelycosaurs took place by the Middle Permian as the world progressively became drier. Gorgonopsians rose to become apex predators of their environments following the extinction of the dinocephalians and large therocephalians after the Middle Permian. Despite the existence of a single continent during the Permian, Pangaea, gorgonopsians have only been found in the Karoo Supergroup(primarily in South Africa, but also in Tanzania, Zambia, and Malawi), the Moradi Formation of Niger, and western Russia, with probable remains known from India. These places were semi-arid areas with highly seasonal rainfall. Gorgonopsian taxa vary very little, and consequently, many species have been named based on flimsy and highly variable differences since their discovery in the late 19th century, and the clade has been subject to several taxonomic revisions

They went extinct during a phase of the Permian–Triassic extinction event taking place at the very end of the Permian, in which major volcanic activity (which would produce the Siberian Traps) and resultant massive spike in greenhouse gases caused rapid aridification due to temperature spike, acid rain, frequent wildfires, and potential breakdown of the ozone layer. The only therapsid group which survived the event was the cynodonts, which would eventually evolve into mammals. The large predatory niches would be taken over by the archosaurs (namely crocodilians and dinosaurs) in the Mesozoic.