Following in the Steps of a Peculiar Protomammal

There’s something undeniably cute about dicynodonts. A case could easily be made that they were the manatees of the Permian and Triassic, protomammal cousins of ours whose barrel-shaped bodies, smushed faces, and tusks gave them their own “so ugly they’re adorable” vibe. Naturally, most of what we know about what they looked like comes from the synthesis of bones and comparative anatomy, but that’s not all. Fossil footprints found in the Late Triassic rock of Argentina’s Los Menucos Group have added a little bit more to our understanding of how these ancient synapsids looked and moved.

The tracks in question, described by paleontologist Paolo Citton and colleagues, can be categorized as Pentasauropus. This is the name given for similar five-toed tracks found in strata of similar age in South Africa, attributed to the shuffling steps of dicynodonts. But, Citton and coauthors point out, there’s something slightly off between the tracks and what was expected of dicynodont posture based on bones alone. The tracks appear to indicate that the animal who made the tracks stood more or less on tiptoe while still but that the whole of the foot – bones and soft tissues – was weight-bearing while the animal moved.

Naturalists have seen this before. The feet of elephants, where comparatively small toes and a fleshy support pad work together, offer a rough approximation of what was going on with the Pentasauropus trackmaker over 200 million years ago. What this may mean, Citton and colleagues propose, is that this kind of specialization allows for larger body sizes – opening up possibilities – rather than directly following increased size as an anatomical coping mechanism. If the dicynodonts had survived longer, perhaps they could have gotten beyond the pig and cow sizes.

What this means is that we not only have a better idea of how these animals looked – their feet bearing fleshy pads that acted as shock absorbers – but also how they moved, plodding along in an elephant-type way despite being significantly smaller. Bones and tracks each have their virtues in isolation, but can even more powerfully refine our picture of the past when they are brought together.