The Ornithosuchids

The Ornithosuchids are a small archosaurian group with only four known genera: Ornithosuchus (the namesake), Riojasuchus, Venaticosuchus, and Dynamosuchus. The Ornithosuchids were quadrupedal but able to move about on their hind legs for short periods of time (perhaps when requiring an extra burst of speed when chasing prey). They were widespread during the Carnian and Norian stages of the Late Triassic. Their skulls resembled those of theropod dinosaurs and - unsurprisingly - they were carnivorous. 

Riojasuchus likely grew to about six feet snout-to-tail

Though they looked similar to other archosaurs – especially the phytosaurs and rauisuchians – they had several distinctive traits. They had a small fenestrae between the palatine and pterygoid bones of their upper mouth; the contact between the nasal and prefrontal bones of the skull is small or absent; they have distinctive downturned snouts; and – most importantly – their ankles are in what’s called a ‘crocodile-reversed’ formation. Archosaur groups in general can be distinguished from one another based on the structure of their ankles. Most archosaurs had a ‘crocodile-normal’ ankle, but Ornithosuchids are unique in that they have a ‘crocodile-reversed’ ankle. 

Ornithosuchus – the group’s namesake – grew to about thirteen feet in length and lived during the Carnian stage of the Late Triassic. Its name means ‘bird crocodile,’ and it had a double row of armored plates along its back. It was originally thought to be the ancestor of the carnosaurian dinosaurs (such as Allosaurus and kin), but it’s now recognized as being more closely related to crocodilians than birds. 

Ornithosuchus feasting on a tusked dicynodont