Living in what is now Lesotho and South Africa during the very early Jurassic, Lesothosaurus diagnosticus is a small species of non-avian dinosaur believed to be among the earliest ornithischians, an order of dinosaurs that, though only distantly related to birds, had bird-like hip joints, and who's later members included the ceratopsians (a group of typically large, quadrupedal dinosaurs with prominent facial horns and bony head crests, including Triceratops and its relatives), thyreophorans (heavily armoured quadrupeds, including Stegosaurus, Ankylosaurus and relatives), pachycephalosaurs (relatively small, bipedal dinosaurs with extremely thick armoured skulls) and ornithopods (a hugely diverse group of 3-toed grazing herbivores, including the hadrosaurs or "duck-billed dinosaurs".) As the bones in its hindlimb were considerably longer and thicker than its short, inflexible forelimbs Lesothosaurus was likely bipedal in life, and like all known ornithischians it possessed a hard bony beak positioned in front of its teeth that likely aided it in grasping and tearing plants, although as its teeth were narrower and sharper than the broad grinding teeth seen in many modern herbivorous vertebrates (as well as most later herbivorous ornithischians,) it is possible that it was an omnivore, feeding both on plants and small animals. Large eye sockets and long hind-legs suggest that members of this species were fast-moving animals that relied on an acute sense of vision to detect predators and locate food, and the discovery of "bone beds" in which the remains of several individuals have been preserved in close proximity to one another suggest that they may have been social. Throughout much of the Jurassic the saurischians (the other major group of dinosaurs, containing the large, long-necked quadrupedal sauropods and diverse bipedal theropods) were considerably more widespread and diverse than the ornithischians, but by the end of Cretaceous the ornithischians had drastically diversified to the point of becoming among the most abundant large land animals - by studying Lesothosaurus and other early ornithischians, a better understanding of the group's rise to prominence (and the resulting impact on wider ecosystems, as plants developed defences against predation and other herbivores adapted to compete) can be gained.
