Introduction

Qantassaurus intrepidus, named after the Australian airline Qantas, was a small ornithopod from the Early Cretaceous of Victoria. The herbivorous Qantassaurus is known only from its unusually short, deep lower jaws with just ten cheekteeth. Qantassaurus was part of a diverse assemblage of small Australian ornithopods that might have been part of the Australian dinosaur fauna since the Jurassic.

Identification

Qantassaurus intrepidus was a small ornithopod, known only from lower jaws and teeth. Contrary to some accounts, no other cranial or postcranial fossils of Qantassaurus have been found. We therefore don't know the size of its orbits, the length of its limbs or its tail type, although we can make an educated guess based on the general characteristics of other small ornithopods. Since long bones of Qantassaurus are not yet known, we have no information on its yearly growth pattern. However, some long bones of other small Victorian ornithopod species show an absence of LAGs (Lines of Arrested Growth), suggesting that these animals were active year-round (and arguably warm-blooded).

Qantassaurus was unique in that it had an unusually short (foreshortened) lower jaw. Diagnostic features of Qantassaurus are as follows: the dentary is foreshortened with dorsal and ventral margins converging towards the front of the jaw, and there are just ten cheekteeth (other small ornithopods have a greater number of cheekteeth and longer, narrower jaws). The teeth of Qantassaurus are almost impossible to distinguish from those of another small Victorian ornithopod, Atlascopcosaurus loadsi (possibly a nomen dubium) although the jaw of Atlascopcosaurus is long, as in other ornithopods. Similarities to the teeth of Gasparinasaura from the Late Cretaceous of Argentina have also been noted. The jaw form and teeth of Qantassaurus are unlike those of Leaellynasaura amicagraphica, the smallest of the Victorian ornithopods. The maxillary teeth of Qantassaurus and Atlascopcosaurus both have at least eight ridges developed on unworn teeth, with a prominent primary ridge; Leaellynasaura has only five ridges on its cheekteeth, and a prominent primary ridge is absent.

Habitat

Southern Victoria during the Early Cretaceous was a rift valley formed between Australia and Antarctica as the two continents slowly split apart. Braided streams and rivers formed extensive floodplains. Large fossilized logs found along the southern Victorian coast suggest nearby forests of araucarian conifers and podocarps. Deciduous ginkgoes were also important forest trees. The understorey would have included pentoxylaeans, ferns, bryophytes and mosses, and horsetails and reeds would have lined the streambanks.

Victoria lay south of the palaeo-Antarctic Circle in the Cretaceous and, although the global climate was much warmer than it is today, the area would have experienced the extremes of daylight typical of polar regions.Evidence for rafting ice in the inland Eromanga Sea and studies of cryoturbation structures (deformations in sediments caused by the seasonal freezing and thawing of soils) suggest that the climate may at times have been quite cold, with winter ice and seasonally frozen ground. However, the presence of lungfish and crocodilians, now known only from warmer regions, suggests a generally milder climate.

Distribution

Qantassaurus intrepidus is known only from the Flat Rocks fossil site near Inverloch (Strzelecki Ranges) on the southern Victorian coast about 150 km south-east of Melbourne.

Feeding and diet

Qantassaurus was a small herbivore that would have eaten edible small, low-growing Early Cretaceous plants such as ferns and horsetails.

Other behaviours and adaptations

Small ornithopods were remarkably common and diverse in Cretaceous Australia, particularly in southern Victoria, and may have travelled in small herds or flocks. Dinosaur burrows, possibly those of small ornithopods, were recently discovered along the southern Victorian coast. Perhaps Qantassaurus and other small ornithopods spent the colder months of the year underground.

Fossils description

The holotype of Qantassaurus is a complete left dentary (NMV P199075) with teeth preserved in seven out of ten alveolar sockets. It was found at the Flat Rocks site (Wonthaggi Formation, Strzelecki Group) near Inverloch, Victoria. Referred specimens include two other isolated dentaries: NMV P198962 (a complete left dentary with four teeth and all alveoli preserved); and NMV P199087 (a fragmentary right dentary). Fossil material of Qantassaurus is held by Museum Victoria in Melbourne, Australia.

Evolutionary relationships

There are perhaps as many as six different types of small ornithopods in Early Cretaceous Australia, all of which are known only from isolated fossil remains. Determining evolutionary and intergroup relationships has therefore been quite difficult. The Victorian ornithopods were first put into Hypsilophodontidae because of similarities in skull and tooth structure to the European hypsilophodontids. ‘Hysilophodontidae’, however, is now thought to be a ‘grab bag’ of unrelated species, and is currently under revision.

The status of Qantassaurus (along with that of Fulgurotherium, Leaellynasaura and Atlascopcosaurus) is currently under review. Although some palaeontologists consider these to be valid species - in spite of being based on fragmentary material - others think there is insufficient diagnostic fossil material to call these valid, distinct species. This account treats Qantassaurus as a valid species until the relationships of small Australian ornithopods are reviewed.

References

Butler, R. J., Upchurch, P. and Norman, D. B., 2008. The phylogeny of the ornithischian dinosaurs. Journal of Systematic Palaeontology 6(1), 1-40.

6(1), 1-40. Coria, R. A. and Salgado, L., 1996. A basal iguanodontian (Ornithischia: Ornithopoda) from the Late Cretaceous of South America. Journal of Vertebrate Paleontology 16(3), 445-457.

16(3), 445-457. Huene, F. von, 1932. Die fossile Reptil-Ordnung Saurischia, ihre Entwicklung und Geschichte. Monograph in Geologie und Paläontologie (Series 1) , 1-361.

, 1-361. Molnar, R. E., 1980b. Australian late Mesozoic terrestrial tetrapods, some implications. Memoirs of the Soc. Geol. Fr . 139, 131-143.

. 139, 131-143. Molnar, R. E., 1991. Chapter 18: Fossil Reptiles in Australia. Pp. 605-701 in Vickers-Rich, P., Monaghan, J. M., Baird, R. F. and Rich, T. H. Vertebrate Palaeontology of Australasia. Pioneer Design Studio, Lilydale, Victoria.

Pioneer Design Studio, Lilydale, Victoria. Molnar, R. E. and Galton, P. M., 1986. Hypsilophodontid dinosaurs from Lightning Ridge, New South Wales, Australia. Geobios 19, 231-239.

19, 231-239. Rich, T. H., 1996. Significance of polar dinosaurs in Australia. Memoirs of the Queensland Museum 39, 711-717.

39, 711-717. Rich, T. H. V. and Rich, P. V., 1989. Polar dinosaurs and biotas of the Early Cretaceous of southeastern Australia. National Geographic Research 5, 15-53.

5, 15-53. Rich, T. H. and Vickers-Rich, P., 1999. The Hypsilophodontidae from southeastern Australia. Pp. 167-180 in Tomida, Y., Rich, T. H. and Vickers-Rich (eds) Proceedings of the Second Symposium on Gondwanan Dinosaurs. National Science Museum of Japan, Tokyo.

National Science Museum of Japan, Tokyo. Rich, T. H., Vickers-Rich, P. and Gangloff, R. A., 2002. Polar dinosaurs. Science295, no. 5557, 979-980.

Further reading