Period: Early Jurassic
Order, Suborder, Family: Ornithischia, Ornithopoda, Fabrosauridae
Location: Africa (South Africa)
Length: 3 1/2 feet (1 meter)
In a series of papers in the early 1970s, Tony Thulborn described the bone structure of the small ornithischian Lesothosaurus, which he then called Fabrosaurus. Peter Galton renamed it Lesothosaurus ("Lesotho reptile," for the country where the first fossils were found).
Lesothosaurus was different from Heterodontosaurus, the other ornithischian that lived at the same time. It did not have the large tusks of Heterodontosaurus. The upper and lower teeth of Lesothosaurus were small and shaped like little arrowheads. Although its teeth did not form an angled grinding surface like those of Heterodontosaurus, the upper and lower teeth did interlock (occlude) and wear against each other when the jaws closed. This formed an efficient way to grind plants. It probably did not have a beak for cropping plants, although a small one might have been present in the lower jaw. Lesothosaurus probably did not have fleshy cheeks, or maybe it had very small ones.
The skeleton of Lesothosaurus was light; it had hollow limb bones and hollow spaces in the skull. The front limbs were small and were probably used for grasping. The hand had four well-developed fingers and a smaller fifth finger.
The back legs were adapted for running. The lower leg (shank) was longer than the thigh, and the long toe bones were arranged so that the long bones of the foot (metatarsals) were off the ground. Lesothosaurus did not have fused bones (bones that had joined together) in the ankle or foot. The fifth toe was very small and higher up on the foot, and the first toe was too short to reach the ground. Lesothosaurus was a quick runner.
The relatives of Lesothosaurus include the first ornithischian, Pisanosaurus, from Argentina. The little armored dinosaur of Arizona, Scutellosaurus, also may belong in this group.