Scutellosaurus

Phylogeny: Dinosauria > Ornithischia > Genasauria > Thyreophora

Overview: Most of the armored dinosaurs best known to the general public were decently large animals. This included the plate-backed Stegosaurus and the tanky Ankylosaurus. Their relatives were similarly impressive or were at least moderately large by today’s standards, but they all shared a common ancestor that was much smaller. Scutellosaurus itself probably wasn’t the direct ancestor of either the stegosaurs or ankylosaurs, but it was closely related to such a creature and gives us a good idea as to what it would’ve looked like. It was a basal member of the Thyreophora, which was a clade containing stegosaurs, ankylosaurs and other armored dinosaurs. Remains that are attributed to Scutellosaurus come from the Kayenta Formation of Arizona, which formed back in the Early Jurassic. Scutellosaurus lived much earlier than its famous, more derived cousins. The creature’s longer legs suggest it even retained the bipedal stance of earlier ornithischian ancestors. Its fossils were first found in the 1970’s, leading to its 1981 description.

Armored dinosaurs were protected by bony lumps, or osteoderms, which grew imbedded within the skin, often forming rows along the back, sides, neck and tail. Osteoderms are far from unique to thyreophorans, having appeared among some sauropods for instance, but they also aren’t unique to dinosaurs as a whole. Crocodiles and alligators, for instance, also have osteoderms over much of their backs. Those on Scutellosaurus were small and rounded in some spots, but somewhat spinier in others, though fairly modest. Its generic name, meaning “small-shielded lizard”, refers to these osteoderms. Dermal armor was of great use to it, since it wasn’t able to ward off predators by sheer size alone. Scutellosaurus was only a little over a meter in length as an adult. In addition to its armor, evasion and camouflage may’ve played some added role in its defense. The same region was also home to the theropod Dilophosaurus, which likely preyed on this animal.