Chilesaurus

Type Species: Chilesaurus diegosuarezi

Classification: Dinosauria 

Time Period: Late Jurassic 

Location: South America 

Diet: Herbivore

Chilesaurus is an oddball of a dinosaur. Reaching ten and a half feet in length, it had spatula-shaped, elongated teeth that obliquely pointed forward, a design perfect for eating plants. Its herbivorous lifestyle is also attested by its backward-pointing pubic bone, which made room for a large gut. Its hind limb wasn’t well adapted for running, and its broad feet had a weight-bearing front toe. It had strong arms with a large claw that could be extended outwards, just as is seen in the sauropodomorphs. All this to say, it looks like a cross between a theropod and an ornithischian, and no one really knows where to place it in the dinosaur family tree. 

Those who argue for a theropod lineage point out that it’s not uncommon – although it’s certainly not usual – for theropods to adapt herbivorous lifestyles. We see this with the therizinosaurs, who became herbivorous, and with the ornithomimosaurs, who became omnivorous. Perhaps Chilesaurus is simply a theropod that went vegan. Others, however, consider the mixture of traits between theropods and ornithischians as evidence that we’ve got the dinosaur family tree all wrong. The current cladogram, which subdivides Dinosauria into the lizard-hipped Saurischians and the bird-hipped Ornithischians, wasn’t the only cladogram proposed; another was proposed by Thomas Huxley in 1869 (and revived by some scientists in 2017). Huxley argued that Dinosauria should be subdivided into Saurischia and Ornithoscelida. In his proposal, Saurischia contained all the sauropodomorphs, and Ornithoscelida contained the theropods and the ornithischians. In Huxley’s scheme, theropods are more closely related to ornithischians than to the sauropodomorphs. Proponents of his view point to Chilesaurus as evidence that his thesis is not only justifiable but correct, and that Chilesaurus, despite its relatively late appearance in the fossil record, is evidence of a ‘vestigial’ family line that eventually gave rise to both ornithischians and theropods.