hypsilophodonts

Hypsilophodonts were a diverse group of small to medium-sized ornithischian dinosaurs that lived during the Jurassic and Cretaceous periods. The name "hypsilophodont" literally means "high-ridged tooth," referring to the distinctive crests on their cheek teeth, which were adapted for grinding plant material. They were generally bipedal herbivores, though some may have been facultatively quadrupedal. Their bodies were typically lightly built, with long hind limbs suggesting agility and speed, likely used to escape predators. Many hypsilophodonts possessed a stiffened tail, supported by ossified tendons, which aided in balance during rapid movement.

Fossil evidence indicates that hypsilophodonts were widespread, with remains found on every continent. Their diet consisted of low-lying vegetation such as ferns, cycads, and early flowering plants. While their exact evolutionary relationships have been debated, they are generally considered basal within the Ornithopoda, a major group of ornithischian dinosaurs that also includes hadrosaurs and iguanodonts. Early members of the group, like Lesothosaurus from the Early Jurassic, were quite small, while later forms, such as Hypsilophodon from the Early Cretaceous, grew to be a bit larger, reaching about 2 meters in length. The group eventually died out by the end of the Cretaceous period, along with most other non-avian dinosaurs.