The Dicynodonts

the elephant-sized Lisowicia

The dicynodonts were cousins to the cynodonts; both were therapsid ‘proto-mammals’ who lived side-by-side in the Permian and Triassic. Though the cynodonts would continue into the Jurassic Period – with an off-branching descendant leading to modern mammals – the dicynodonts didn’t make into the second period of the Mesozoic. The dicynodonts ranged from size from that of modern rats to modern elephants, and they were the most diverse branch of proto-mammals. 

Stepping onto the world stage in the Middle Permian, they launched a rapid diversification program and became the dominant herbivorous creatures of the Late Permian. This was their heyday, for they were crippled by the Permian-Triassic Extinction: only four lineages survived into the Triassic. Three of these didn’t last long (including the infamous Lystrosaurus that dominated the herbivorous niches of the Early Triassic), but the fourth received a second wind. The Kannemeyeriiformes were stocky, pig- to ox-sized animals that flourished during the Early and Middle Triassic before dwindling in the Late Triassic. Their demise has been attributed to the spread of plant-eating cynodonts and herbivorous rhynchosaur reptiles. Their numbers waned in competition with these upstarts, but it wasn’t until the Middle Triassic that they received a knock-out punch by the arrival not only of large herbivorous dinosaurs – such as the prosauropods – but also by the diversification and specialization of theropod dinosaurs that preyed on dicynodonts. The dicynodonts went extinct towards the end of the Late Triassic.

Lystrosaurus: Early Triassic Heavyweight

Dicynodonts were short, strong, and barrel-shaped with strong limbs, and they’re easily recognized by a pair of tusks (from whence derives their name, meaning ‘two dog tooth’). These tusks may have been used to root through soils, to defend against predators, or to compete for mates. Paleontologists believe the differing size of tusks among fossils may represent sexual dimorphism (for example, females may have had smaller tusks – or no tusks at all! – whereas males developed busty tusks  for show). Dicynodont skulls were light but strong, and the synapsids temporal openings in the rear of the skull had enlarged to allow stronger jaw muscles. The front of the skull and their lower jaws were narrow and, in all but a handful of earlier forms, toothless. Most dicynodonts utilized a horny beak at the front of their mouth used to shear plant material. Dicynodonts may have been warm-blooded: they had highly vascularized bones (like warm-blooded mammals), and studies of Permian coprolites littered with the bones of dicynodont prey mixed with hair may indicates dicynodonts had hair (again, like warm-blooded mammals). Skepticism towards their warm-bloodedness is argued by the fact that studies on Late Triassic dicynodont coprolites show digestive patterns more typical of cold-blooded animals; however, we must remember that if dicynodonts developed warm-bloodedness, that doesn’t negate the fact that they were in ‘transition’ – we can expect a hybrid of features usually associated with both cold- and warm-blooded organisms. In support of their warm-bloodedness was a study using chemical analysis that suggested both dicynodonts and their cynodont cousins developed warm-bloodedness independently prior to the Triassic. 

a cynodont (left) and dicynodont face off