In Depth
Heterodontosaurus is one of more popular ornithischian genera thanks to the mixture of teeth in the mouth. Heterodontosaurus had blade-like incisor teeth and chisel-like molar teeth within the mouth for processing food by slicing and grinding respectively. The show stealing features of the mouth however are the large tusks in the anterior (front) of the mouth. The presence of these tusks means that Heterodontosaurus had three separate kinds of teeth within its mouth, something that is very unusual for a dinosaur.
The tusks of Heterodontosaurus have been the largest source of confusion for this genus since there are too very good theories that explain their presence. The first is that they were feeding aids that were used like digging tools, such as for the purpose of digging up plant roots and tubers or breaking down the walls of termite mounds. Another theory though is that the tusks may have been only present upon the males, and that the tusks were used for display and possibly in fights between rival males. Unfortunately we cannot yet say for certain which, or possibly even a degree of both is more correct, but we do now know that the large canines were also present in juveniles.
It is easy to get hung up upon just studying the teeth of this dinosaur, but there are also a number of other interesting things to consider about the genus. One is that Heterodontosaurus is one of the earliest known ornithischian (bird hipped) dinosaurs. We also do not know for certain what Heterodontosaurus ate. Later ornithischians such as stegosaurs, hadrosaurs and ceratopsians are all known to have been herbivorous, only eating plants, but due to its early appearance in the ornithischian line, it begs the question was Heterodontosaurus an exclusive herbivore? This is because Heterodontosaurus would in evolutionary terms been closer to meat eating ancestors, and while the teeth towards the rear of the mouth would have been well adapted for processing plant matter, they could have been used for processing the flesh of small vertebrates like lizards and very primitive mammals. In addition to this, Heterodontosaurus might have even supplemented their diets by scavenging carrion. Until better preserved remains are found, all options regarding diet remain of the proverbial table.
Heterodontosaurus also had very unusual hands for dinosaurs. All five fingers were present, but the key thing here is that two of the fingers were opposable to the others. This means that Heterodontosaurus would have had the ability to pick up small things with just one hand instead of have to use both to press upon them from either side. Again this also suggests that Heterodontosaurus could have eaten more or less anything of their choosing. Only a few other genera of dinosaurs such as Troodon are known to have had hand digits that were opposable to the others.
Although an early dinosaur, another question about Heterodontosaurus is did it have feathers? In this respect feathers would be very primitive in form and analogous to hairs. Such feathers now seem to have been very common in small to medium sized theropod dinosaurs of the saurischian line, but are not that well known in ornithischians. However, Heterodontosaurus had a relative genus of heterodontosaur living during the later Oxfordian stage of the Jurassic named Tianyulong. This relative is known to have had a covering of feathers on its body, indicating that the genetic requirements for feather growth are not exclusive to the theropod dinosaurs, and probably have origins all the way back to the earliest dinosaurs and perhaps even beyond to when the synapsids diverged away from reptiles to produce the ancestors of mammals. As for Heterodontosaurus, we don’t know for certain if it had feathers, though the presence of primitive hair-like feather structures is now a possibility for this genus.
Heterodontosaurus fossils are best known from South Africa, and since these date to sometime between 199-196 million years old, this firmly establishes that Heterodontosaurus lived during the early Sinemurian of the Jurassic. There are however possible further remains of Heterodontosaurus located in Argentina and Mexico. Incomplete remains from Argentina have been identified as being very similar to Heterodontosaurus, though they are too incomplete to positively ascertain whether they are of the same genus or a close relative of. If they are then the Heterodontosaurus genus may extend all of the way back into the Norian stage of the Triassic. Further incomplete remains have been discovered in Mexico, and though these have been labelled as Heterodontosaurus, they are too incomplete to identify a specific genus. Again, if correct, then the Mexican material may extend the temporal range of the Heterodontosaurus genus into the Pleinsbachian of the early Jurassic.
Further Reading
– A new ornithischian from the Upper Triassic of South Africa - A. W. Crompton & A. J. Charig - 1962. - A complete skeleton of the Late Triassic ornithischian Heterodontosaurus tucki - A. P. Santa Luca, A. W. Crompton & A. J. Charig - 1976. - Fossils from the Elliot and Clarens Formations (Karoo Sequence) of the northeastern Cape, Orange Free State and Lesotho, and a suggested biozonation based on tetrapods. - J. W. Kitching & M. A. Raath - 1984. – A heterodontosaurian ornithischian in the Upper Triassic of southern Patagonia? - A. M. B�ez and C. A. Marsicano - 1998. - New heterodontosaurid specimens from the Lower Jurassic of southern Africa and the early ornithischian dinosaur radiation. - L. B. Porro, R. J. Butler, P. M. Barrett, S. Moore-Fay & R. L. Abel - 2011.
