Inostrancevia alexandri assaulting Scutosaurus karpinski

The Therapsids, ancestors of the present day mammals dominated the terrestrial fauna of the late Permian era around 250 million years ago..

But one group of reptiles, the Anapsids had also evolved into ecological niches and prospered. Herbivorous Anapsid types attained huge bulk to accommodate the mass of guts needed to digest difficult plant material and discourage attack from predators. But as the fossil record has shown again and again, bigger herbivores generally results in a corresponding increase in the size of the carnivores that eventually preyed on them.

Cow-sized Scutosaurus karpinski was one of the larger members of the herbivorous group Parieasauria. Scutosaurus had flat multi-cusped teeth reminiscent of an Iguana.  Their limb bones showed  graviportal or weight bearing adaptations. These limbs  were large and stout with a reduced number of phalangeal  bones making their toes short and stubby, more pedestal like. and therefore more able to support huge bulk.

All Parieasaurs were covered with polygon-shaped bony scutes which served as protection as well as reinforcement, helping to literally rivet the heavy hide to the skeleton and provide overall support for the bulky viscera (guts) and stiffening to the massive body. 

One of the likely predators of Scutosaurus was Inostrancevia alexandri, whose remains have been found in the same formations as Scutosaurus. About the size of a lion, and endowed with stout stabbing fangs, Inostrancevia seems well adapted to prey upon the abundant thick-skinned Parieasaurs and Dicynodonts.

 Take a huge bite and gulp it down seems to have been the preferred method of feeding for Inostrancevia as lateral chewing teeth in the jaws were puny to non- existent. 

Inostrancevia was an active predator as evidenced by the vertical stance, a much more efficient system for locomotion that did not require as much energy output as a sprawling gait would. The tail was also shorter and was probably held more upright than earlier sprawling predators.