• Question from:Ian

I know that crocodilians are universally considered archosaurs.  However, to my understanding one of the key traits of the archosaurs is the antorbital fenestra, a trait I have not seen on the skulls of crocodilians.  What is the reason for this and what other traits identify them as members of the Archosauria?

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  • QMUL, London
  • Posts: 1,022

Ah well the thing is that the antorbital fenestra is not present in living crocodiles as it was lost during their evolution. However, it was present in the ancestral crocodiles. Obviously whales are still mammals and evolved from mammalian ancestors even if they have lost their fur and back legs (otherwise characteristics of mammals), so modern crocs are still archosaurs even if they have lost their antorbital fenestra.

Slightly unhelpfully, there are two definitions of archosaurs out there so the characters vary slightly depending on which definition you use, though in either case, crocs are still archosaurs. They do still have teeth set in sockets (the thecodont condition) unlike things like lizards where they grow right out of the bone, and a fenestra in the jaw and have a flange on the femur (thigh bone) called the 4th trochanter. So while the antorbital fenestra is gone, they still have the other key characters of archosaurs, as did their ancestors, so they are still archosaurs.