Lesothosaurus diagnosticus (Galton 1978 ) Hettangian to Sinemurian, Early Jurassic ~200 mya, 1 m in length was a small primitive ornithischian dinosaur. Derived from a sister to Heterodontosaurus, Lesothosaurus phylogenetically precede .Scutellosaurus and Stegosaurus.
Two distinct skulls shapes have been reported for Lesothosaurus, one with a longer, lower rostrum and one with a shorter, rounder rostrum.
Distinct from Heterodontosaurus, the skull of Lesothosaurus was relatively smaller and shorter. The rostrum was straighter and more pointed. As a consequence, the naris was lower. The postnarial process of the premaxilla was reduced. The jawline was straight. The antorbital fenestra was a tiny spot in the middle of the deep triangular fossa. The quadratojugal not so robust or tall and it retained the original ventral connection to the jugal, as in Daemonosaurus, without creating an accessory connection, as in Heterodontosaurus. The teeth were smaller and leaf-shaped.
The neural spines and caudal chevrons were more gracile.
The forelimbs were shorter and the hand was smaller with shorter fingers and without trenchant claws (judging by the one ungual that is known).
The posterior ilum was shorter. The pubis developed an anterior process and, overall, was much more slender. The hind limbs were more gracile. |
