Non-crocodilian Face

Holotype as depicted in von Baczko and Desojo, 2016

The holotype skull of Riojasuchus is very non-crocodilian to the casual observer. Having previously been associated with a number of people interested in crocodiles this skull shapes is not very alien to me and others that have experiences like mine. This is far from the strangest of crocodilian ancestors of course and we have discussed others here before (such as Simosuchus). The ancestral variations and resulting evolutionary history of crocodilians is actually quite fascinating. Riojasuchus is somewhere in the middle of this history. It is, obviously I think, not quite a crocodile and not one of the "primitive" herbivorous crocodilian ancestors. Further separating Riojasuchus from its descendant cousins (possibly a more appropriate description than saying it is directly ancestral to crocodilians) is the tree of Butler et al. (2011) which describes Riojasuchus (and ornithsuchidae) as a lineage that ends without more descendant lineages. Regardless of whether Riojasuchus has extant descendants or not, the skull shape is decidedly non-crocodilian, which is what we wanted to look at specifically today. The teeth are more crcodilian than some other crocodile ancestors. The dorsoventrally tall skull is quite distinct from living crocodilians. The transition from skulls of this shape to the more familiar flattened skull of crocodilians is the subject of much ongoing inquiry and research. It is a long, complex story, and we are still learning quite a lot from this group of animals about how and why head shape changes, or does not, over the evolution of a group.

Butler, R. J., Brusatte, S. L., Reich, M., Nesbitt, S. J., Schoch, R. R., & Hornung, J. J. (2011). The sail-backed reptile Ctenosauriscus from the latest Early Triassic of Germany and the timing and biogeography of the early archosaur radiation. PloS one, 6(10), e25693. doi:10.1371/journal.pone.0025693

Nesbitt, S. J., Desojo, J. B., & Irmis, R. B. (2013). Anatomy, phylogeny and palaeobiology of early archosaurs and their kin. Geological Society, London, Special Publications, 379(1), 1-7.