Heterodontosaurus

Heterodontosaurus is a heterodontosaurid genus from the Early Jurassic, which lived approximately 200–190 million years ago. The genus has only one species, Heterodontosaurus tucki, which was discovered and scientifically described by Alfred Walter Crompton and Alan J. Charigin in 1962 in South Africa during the British-South African Expedition, and was described by a crushed, but almost complete fossilised skull.

The type specimen was revealed and excavated on the altitude of 1890m, in Tyinindini (Transkei District, Cape Province, South Africa), and it is stored in the Iziko South African Museum. The name Heterodontosaurus means „different toothed lizard”, referring to its unusual dentition, and the species name was given after george C. Truck, who financially supported the expedition^[1]. Later further fossils of the species have been found, amongst them a skeleton which was nearly complete in 1966, and the description of postcranial skeleton was subsequently published by Albert Santa Luca, Crompton and Charig in 1976^[2].

Heterodontosaurus tucki. Source: By FunkMonk (Michael B. H.) - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=44921379

Known occurrences of Heterodontosaurus fossils.

Description and anatomy

Heterodontosaurus was not a huge sinosaur; it had a length between 1.18 m and 1.75 m, and weighed between 2 and 10 Kilograms. These data shows a big difference between different specimens, but based on osteological evidences, we know that these were adults^[3]. However, with these parameters Heterodontosaurus was one of the largest species within Heterodontosauridae, and it was amongst the smallest Ornitischia at the same time. It had an elongated, narrow, small but robust skull, with a horny beak at the anterior parts of the jaws, three types of teeth within; incisor-like teeth at the front (these were present only in the upper jaw), followed by canine-like tusks, and chisel-like cheek-teeth behind them.

The animal had a short body with a long tail, five-fingered forelimbs and four-fingered hindlimbs, these latter were longer and slender. Probably they were bipedal animals. Despite their long tusks they were likely herbivorous, or maybe omnivorous. Since an other member of the family, named Tianyulong, which was described in 2009^[4], was fossilized wit hundreds of long, filamentous, brisltle-like integuments on its back, Heterodontosaurus also has been illustrated with similar structurs.

Taxonomy

Heterodontosaurus tucki is the best known member of the Heterodontosauridae, which is considered to be a basal group of ornithischian dinosaurs. When it was described in 1962, based on certain characteristic similarities, the new genus (and consequently the new species within it) was placed within the Ornithopoda first, as a primitive member of the group^[1]. Some later, in 1966, Heterodontosauridae was presented as a family within the Ornithischia.

The new family included not only Heterodontosaurus, but also Lycorhinus, which was classified as the closest relative of Heterodontosaurus^[5][6]. The family was recognised as an independent clade by Sereno in 1998 and 2005. Though the exact relationships between Heterodontosauridae and other ornithischian dinosaurs was debated for long, it was clear, that they had key importance in understanding the evolution adn relationships of Orithischia.

Heterodontosaurus tucki head reconstruction and skull. Source: By Tyler Keillor - Sereno PC (2012) Taxonomy, morphology, masticatory function and phylogeny of heterodontosaurid dinosaurs. ZooKeys 226: 1-225. doi:10.3897/zookeys.226.2840., CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=21907098

Paleobiology

Despite their long tusks, Heterodontosaurus weas probably herbivorous, or maybe omnivorous. Earlier it was thought that these tusks had no important role in feeding, and they were rather used in the defence of the anumal, or during fight between conspecifics, like in case of today-living muntjacs or chevrotains^[7]. However, more recently several studies concluded that this dinosaur might have been omnivorous, and occasionally hunted and killed its prey using these tusks^[8][9]. Furthermore, considering that the enlarged tusks were present even in young specimens, its function in combat with conspecifics or its role in sexual dimorphism seems to be unlikely. Consequently, the role of their tusks in feeding or defence against predators was more probable^[9].

Heterodontosaurus had relatively long arms with large and curved claws, and long hindlimbs suitable for fast running. These features and the tusks could have made this dinosaur highly capable of hunting for smaller animals. This could mean an evolutionary advantage for Heterodontosaurus over strictly herbivorous dinosaurs during dry seasons, when there was fewer vegetation available for feeding.

Heterodontosaurus tucki skeleton. Source: By Daderot - Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=37559701

Scientific references

[1] Crompton, A.W.; Charig, A.J. (1962): A new ornithischian from the Upper Triassic of South Africa. Nature. 196 (4859): 1074–1077. doi:10.1038/1961074a0

[2] Santa Luca, A.P.; Crompton, A.W.; Charig, A.J. (1976): A complete skeleton of the Late Triassic ornithischian Heterodontosaurus tucki. Nature. 264 (5584): 324–328. doi:10.1038/264324a0

[3] Galton, P.M. (2014): Notes on the postcranial anatomy of the heterodontosaurid dinosaur Heterodontosaurus tucki, a basal ornithischian from the Lower Jurassic of South Africa. Revue de Paléobiologie, Genève. 1. 33: 97–141.

[4] Zheng, Xiao-Ting; You, Hai-Lu; Xu, Xing; Dong, Zhi-Ming (2009): An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures. Nature. 458 (7236): 333–336. doi:10.1038/nature07856

[5] Romer, A.S. (1966): Vertebrate Paleontology (3rd ed.). Chicago: University of Chicago Press. 468 pp. ISBN 978-0-7167-1822-2.

[6] Kuhn, O. (1966): Die Reptilien. Verlag Oeben, Krailling near Munich, 154 p.

[7] Thulborn, R.A. (1974): A new heterodontosaurid dinosaur (Reptilia: Ornithischia) from the Upper Triassic Red Beds of Lesotho. Zoological Journal of the Linnean Society. 55 (2): 151–175. doi:10.1111/j.1096-3642.1974.tb01591.x

[8] Norman, D.B.; Crompton, A.W.; Butler, R.J.; Porro, L.B.; Charig, A.J. (2011): The Lower Jurassic ornithischian dinosaur Heterodontosaurus tucki Crompton & Charig, 1962: Cranial anatomy, functional morphology, taxonomy, and relationships. Zoological Journal of the Linnean Society: 182–276. doi:10.1111/j.1096-3642.2011.00697.x

[9] Butler, R.J.; Porro, L.B.; Norman, D.B. (2008): A juvenile skull of the primitive ornithischian dinosaur Heterodontosaurus tucki from the 'Stormberg' of southern Africa. Journal of Vertebrate Paleontology. 28 (3): 702–711. doi:10.1671/0272-4634(2008)28[702:AJSOTP]2.0.CO;2