Deuterosaurus Temporal range: Capitanian
Deuterosaurus biarmicus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Synapsida
Clade:	Therapsida
Suborder:	†Dinocephalia
Family:	†Deuterosauridae
Genus:	†Deuterosaurus Eichwald, 1846
Type species
Deuterosaurus biarmicus Eichwald, 1846
Species
D. biarmicus Eichwald, 1846 ?D. jubilaei (Nopcsa, 1928) D. seeleyi Nopcsa, 1902

Deuterosaurus is an extinct genus of dinocephalian therapsids, one of the non-mammalian synapsids dominating the land during the late Paleozoic.

Deuterosaurus comes from Greek δευτερος "second" and σαυρος "lizard".^[1]

• Deuterosaurus biarmicus, the type species of Deuterosaurus, was named by Eduard Eichwald in 1846 based on a series of vertebrae and ribs.^[2][3] Efremov erroneously listed "Deuterosaurus mnemionalis" as a synonym of D. biarmicus, although no such species was ever named.^[4]
• Deuterosaurus seeleyi was named by Franz Nopcsa in 1902, based on a specimen consisting of 13 ribs.^[5]
• Deuterosaurus jubilaei was named by Nopcsa in 1928, originally as representing a distinct genus, Mnemeiosaurus. Boonstra^[6] and Tchudinov^[7] agreed that Mnemeiosaurus and Deuterosaurus were distinct genera, whereas Efremov^[8] and Ivakhnenko^[4] considered Mnemeiosaurus a synonym of Deuterosaurus, albeit with D. jubilaei still a distinct species.
• Deuterosaurus gigas was named by Ivan Efremov in 1954 based on teeth. It was later reassigned to Ulemosaurus^[9]

Skulls of Deuterosaurus are well known from several finds. It is over 10 inches (25 cm) high,^[10] with a long snout and conical teeth. Like all anteosaurs, the skull possessed long, dagger-like canine teeth. The skull was rather short for an anteosaur, with a broad cheek region, indicating a very strong bite. The eyes were partly slanted forward, giving it at least partial stereo vision. The pineal eye, though small, had a well formed opening right atop the brain case.

Deuterosaurus was a very large animal, the size of a modern grizzly bear. T. H. Huxley mistakenly considered it to be a dinosaur.^[11] Judging from related therapsids, the short but massive legs were held splayed, much like a modern crocodile. When walking, the tail would have swung sideways, like in modern reptiles.

Deuterosaurus is found in what is now Siberia, which in the Permian was dominated by temperate lowlands. Deuterosaurus was among the largest animals of its day, and has variously been interpreted as a herbivore or carnivore. While the large canines may indicate the ability to kill prey, the short legs and massive body would have made it unsuited as a long distance runner, and better suited to eating plants. Then again, the possible stereoscopic vision again indicates an ambush style carnivore, and the rather blunt, cone-like post canine teeth can be interpreted both ways. Possibly Deuterosaurus was omnivorous, like a modern bear.

Deuterosaurus, like all its therapsid cousins, probably laid eggs. A remarkable thickening of the skull above the eyes indicates it may have engaged in head-butting, possibly in connection with mating or territorial disputes.

• List of therapsids