Tichosteus (meaning "walled bone") is a genus of herbivorous dinosaur from the Late Jurassic. It is known only from vertebrae recovered from Kimmeridgian rocks in the Morrison Formation, Colorado. In 1877 Edward Drinker Cope named the type species Tichosteus lucasanus. The generic name is derived from Greek teichos, "wall", and osteon, "bone", referring to the fact that the vertebrae, though hollow inside, had no lateral pneumatic foramina, openings in the side wall for air sacks to invade the bone. The specific name honours superintendent of public schools Oramel W. Lucas, who collected two vertebrae for Cope, near Arkansas River. The dorsal vertebrae, together forming the holotype AMNH 5770, are about 23 millimetres (0.91 in) long. Cope estimated the size of the animal as that of an alli