Last week I gave you this crocodilian skull from the Grant Museum of Zoology to see if you had any thoughts about which species it might be:

It turns out that you did indeed have some excellent thoughts about the identification, with Cindy Nelson-Viljoen immediately getting it right, with astute observations from David Godfrey and palfreyman1414, plus another correct responses from Joe Vans (as well as Tone Hitchcock and Henry McGhie not via the comments section).

This is a skull of the Dwarf Crocodile Osteolaemus tetraspis Cope, 1861. It’s small size is the first clue, but given how crocodiles grow this could pass as the skull of a young individual of a much larger species. As David Godfrey pointed out, there may be some paedomorphism (where adults look like juveniles) in effect in this species, since the adults as well as being small, have relatively short snouts and big eyes – which are features of juvenile animals as you can see in this display of crocodile development I did for Dinosaurs! Monster Families just before leaving the Horniman:

Part of my reason for wanting to show you this specimen was to force myself to look for some good online resources to get more familiar with crocodilian morphology. As it turns out, I did find a very useful comparative image, which shows the size and shape of the mandibular foramen (a large gap between the bones in the side of the lower jaw) is a helpful feature:

Figure from Walmsley et al (2013): Why the Long Face? The Mechanics of Mandibular Symphysis Proportions in Crocodiles. PLoS ONE 8(1): e53873, doi:10.1371/journal.pone.0053873

In this species the foramen is small, which when considered with the overall proportion is quite distinctive. Of course, this image does not include all 24(ish) living crocodilian species, but it does provide a pretty good range. Hopefully this will help speed up future croc skull identifications, at least allowing certain species to be discounted.

If you have any good tips for crocodile identification please share below!