Agilisaurus

Phylogeny: Dinosauria > Ornithischia > Genasauria > Neornithischia

Overview: Agilisaurus was a relatively small and obscure herbivorous dinosaur that lived in what is now southern China, back in the Middle Jurassic. Length estimates put it about two meters long. Its build was light and slender, which combined with it being a biped, probably implies it could move at a decent speed. Agilisaurus, the “agile lizard”, was named for this inference. Without armor or horns, the only real means of defense it had was either evasion or camouflage. Agilisaurus was likely a source of food for many theropods in its environment. This could’ve included the medium-sized theropod Gasosaurus or possibly the far larger Yangchuanosaurus, though the latter is usually found within geologically younger sediments. Agilisaurus coexisted with other herbivorous dinosaur as well. This may’ve included the stegosaur Huayangosaurus or the fairly basal sauropod Shunosaurus.

Researchers can’t agree on how Agilisaurus should be classified. Most suggest that it belonged to the clade Neornithischia, which was a broad group that contained the lineage leading to “duck-billed” dinosaurs, and the lineage from which the horned ceratopsians evolved. Armored dinosaurs like the stegosaurs and ankylosaurs are excluded from the Neornithischia. It’s possible that Agilisaurus had some form of bristle or fur-like proto-feathers, like some other neornithischians. Some researchers place Agilisaurus close to the ceratopsians and pachycephalosaurs, but this is debated. Agilisaurus fossils were first recovered back in the 1980’s, in the Chinese province of Sichuan. All known fossils come from the lower levels of the Shaximiao Formation. One specimen is known, though it’s quite well preserved and nearly complete, in spite of the confusion surrounding its exact phylogeny.