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Glanosuchus macrops



Kudos to you if you've ever heard of this one!  Glanosuchus was a therocephalian, living in (what is now) South Africa, in the Late Permian, about 260 million years ago.  For its time it was quite sophisticated.  It has signs of a fast metabolism and probable 'warm-blooded'-ness.  I take a guess in reconstructing it with hair.  Glanosuchus was about the size of a wolf, with a skull 30 cm in length.  It had long, sabre-like canine teeth, and must have been a fearsome predator.  It didn't yet have 'chewing' cheek teeth and probably gulped its food down.  It didn't have a bony secondary palate like some later therocephalians had, and thus couldn't breathe while its mouth was full of food.  But it had fine ridges in its nose cavity called maxilloturbinates; in mammals these are used to moisten air breathed out so as to prevent drying-out of their tissues; this indicates a fast rate of breathing, and a higher metabolic rate than those of for instance lizards.

Glanosuchus had 'ears' that were intermediate between those of primitive synapsids and mammals.  Instead of an eardrum, a thin plate of bone at the back of its jawbone conducted vibrations to a hollow space inside its skull which connected with the inner ear by means of the small bones called the stapes.  In modern mammals, the rearmost two bones from the jawbone, the quadrate and articular, detached from the jaw articulation to become the malleus and the incus, which together with the stapes (which became smaller still than they were in Glanosuchus), amplify sounds conducted to the inner ear.

Despite its advanced (for the time) features, Glanosuchus like the other therocephalians were not on the main line of mammalian evolution; the closely related Cynodonts were the ones that eventually yielded the true mammals.
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