Chimaerasuchus

As you can guess from the full name of this creature--Chimaerosuchus paradoxicus, which roughly translates as "crazy mixed-up crocodile"--Chimaerasuchus has posed a puzzle to paleontologists ever since its discovery (in fact, its remains were first thought to be those of a therapsid, or mammal-like reptile). It's clear from the flat molars in the back of this prehistoric crocodile's mouth that it subsisted on plants, rather than fish, shellfish or carrion, like most other Cretaceous crocs. Otherwise, though, Chimaerasuchus appears to have been indistinguishable from its carnivorous crocodilian cousins, though it may have reared up on its hind legs every now and then to reach tasty leaves.