Dino of the Week: Heterodontosaurus

Type Species: Heterodontosaurus tucki

Classification: Dinosauria - Ornithischia - Heterodontosauridae

Time Period: Early Jurassic

Location: South Africa

Diet: Herbivore or Omnivore

Heterodontosaurus was an early ornithischian dinosaur that lived during the Hettangian and Sinemurian stages of the Early Jurassic some 200-190 million years ago. Its remains are part of the Upper Elliot Formation of South Africa; its environment was semi-dry, and it lived among prosauropods and other early ornithischians. The number of different ornithischian species in its habitat implies that ornithischians diversified wildly in the Early Jurassic, setting the stage for their continued dramatic variation throughout the Mesozoic, and that they were able to co-exist because of niche partitioning (while these early ornithischians were all herbivorous or at least omnivorous, they would’ve ‘shared’ the environment by different species focusing on different foodstuffs). 

Several Heterodontosaurus individuals have been found, including a complete skeleton (a rarity for fossilization). These individuals come in two different ‘sizes’, and though this may indicate two different species – one larger than the other – most paleontologists believe it’s a matter of sexual dimorphism. Sexual dimorphism refers to anatomical differences between males and females of the same species, usually in regards to height or size but which can also be present in ornamentation. Sexual dimorphism is common among gregarious (i.e. ‘social’) animals, so sexual dimorphism in Heterodontosaurus would imply that they lived in groups. These animals reached between four feet and five and a half feet in length and weighed between four and twenty-two pounds. Their bodies were short with flexible tails. Their five-fingered forelimbs were long and robust and capable of grasping. The hind limbs were long, slender, and four-toed. Their skulls were elongated and narrow, and they were triangular when viewed from the side. Most scientists believe Heterodontosaurus had long, hollow, feather-like fibers over much of its body. These fibers haven’t been preserved in these South African specimens, but a heterodontosaur cousin in China – Tianyulong – had such feather-like fibers. Though Heterodontosaurus lived sixty million years before its Chinese cousin, scientists believe it’s not unreasonable to assume this is a shared characteristic and perhaps even a derived facet of heterodontosaurs in general. 

Heterodontosaurus’ name means ‘different toothed lizard,’ a reference to the fact that it had heterodont (or ‘mismatched’) teeth. Most dinosaurs have a single kind of tooth in their jaws, but Heterodontosaurus and its heterodontosaur kin had three: it had small, incisor-like teeth in the upper jaw; these were followed by long, canine-like teeth and chisel-like cheek-teeth hidden behind its fleshy cheeks. The presence of different types of teeth is rare for dinosaurs and reptiles but common in mammals. Heterodontosaurus’ beaked tip of the snout was toothless. Despite the presence of serrated teeth, it’s believed that Heterodontosaurus was nevertheless herbivorous or at least omnivorous. Some speculate that it used its blade-like canines to sift through topsoil, scrounging for roots or other foodstuffs. Some have even argued that the beak was used to break into termite mounds. Heterodontosaurus’ tooth replacement was sporadic, unlike its relatives.