Therocephalian

Therocephalian were venomous, carnivorous mammal-like reptiles from the Permian and Triassic period.

Characteristics
Therocephalians were quadrupedal creatures which were anatomically similar to Gorgonopsids, albeit with stubbier, thicker legs and a smaller body. They possessed large skulls, which were ridged from the neck, and had a broad, blunt snout with long, straight canines. Therocephalians also had a grooved ridge inside their mouth for injecting venom into their prey. When placid, Therocephalians were slow-moving, but could give surprising bouts of speed and strength when closing in on prey.

Real life
Therocephalians (name meaning "beast-heads") were an extinct suborder of eutheriodont therapsids, which lived from approximately 265 to 245 million years ago. They were named after their large skulls, which, along with the structure of their teeth, suggest that they were successful carnivores. The Therocephalians were more closely related to cynodonts, which would give rise to mammals, than any other group. Therocephalians lived in large numbers in what is now the Karoo of South Africa, but Therocephalian fossils have also been found in Antarctica, Russia and China.

Trivia
Because the Therocephalians were shown to sleep in bright daylight, it has been suggested that they were either nocturnal or were suffering from a form of jet lag after coming through the Anomaly.

The only real-life Therocephalian species to be venomous was Euchambersia, suggesting that this was the Therocephalian species featured in the show.

While not identified in the show, concept art labels them as thrinax, likely beign short for Thrinaxodon.

Errors
The Therocephalians in Primeval were depicted with external ears, when in real-life they would have had internal ears, like lizards.