Dinosaurs - Diamantinasaurus matildae

Introduction

Diamantinasaurus matildae is a titanosaur discovered near Winton in central Queensland . This solidly-built animal was about 15 metres in length and would have been comparatively small for a titanosaur. The bones of Diamantinasaurus (nicknamed ‘Matilda’) were found with those of the theropod Australovenator (‘Banjo’) in the remains of an ancient oxbow lake.

Identification

Diamantinasaurus matildae was a titanosaur, a group of sauropods known mainly from Gondwanan continents. Titanosaurs included the largest terrestrial animals known, with some members reaching up to 35 metres in length and 100 tonnes in weight. Diamantinasaurus was a relatively small titanosaur, from 15 to 16 metres in length and only 15 to 20 tonnes in weight. Fossils of Diamantinasaurus include a near-complete forelimb, ribs, pelvic girdle and upper hind limb.

Diamantinasaurus is assigned to the Lithostrotia (‘Titanosauridae’ + Saltasauridae), titanosaurs characterised by having bony osteoderms in the skin (‘litho’ meaning ‘stone’, and ‘strotia’ referring to skin). Although Diamantinasaurus has been reconstructed with rows of osteoderms along its back, no osteoderms have yet been found.

Unique features of Diamantinasaurus include retention of metacarpal (hand bones) phalangeal facets and phalanges (fingers), with McII heavily reduced; possession of a manual ungual claw; flat distal humeral condyles; and subequal distal femoral condyles. Key features of the skull and dentition, however, can’t be assessed since cranial material has not yet been recovered.

Habitat

The Winton Formation is made up of sandstones, siltstones and claystones formed during the Late Cretaceous period (about 90 million years ago). At this time, the region was an extensive river plain within the lowlands left behind by the retreating Eromanga Sea. The environment would have been a mosaic of large, winding rivers, freshwater pools, oxbow lakes, swamps and coastal estuaries (a spectacular ‘dinosaur stampede’ was recorded in a mudflat deposit from the Winton area - known as the Winton Trackway). The climate would have been subtropical to temperate, with marked seasons and abundant rainfall. Fossil plants from the Winton Formation include angiosperms, araucarian conifers, ginkgoes and ferns. Australovenator, Diamantinasaurus, Savannasaurus and Wintonotitan are from the basal part of the Winton Formation, not far from the type locality of Lovellea wintonensis (an early flowering plant).

Distribution

Diamantinasaurus comes from the Winton Formation of central Queensland, Australia.

Feeding and diet

Sauropods were herbivores. However, there is little direct evidence of food preference other than tooth shape and wear facets. Edible plants known from the Winton Formation or from other areas of Cretaceous Australia include araucarian conifers, angiosperms, ginkgoes, cycads, ferns and horsetails. Unfortunately, since the skull and dentition of Diamantinasaurus are not preserved, its specific diet is unknown.

Although described as ‘hippo-like’, Diamantinasaurus was almost certainly terrestrial. Early hypotheses about a semi-aquatic lifestyle for sauropods have largely been abandoned in favour of a primarily terrestrial lifestyle for most species.

Fossils description

Diamantinasaurus is known from a complete front limb and shoulder girdle, ribs and possible gastralia; a complete pelvic girdle, and the upper hind limb.

Fossils of Diamantinasaurus are held by the Australian Age of Dinosaurs Museum of Natural History in Winton, Queensland. Material was excavated and prepared in a joint Queensland Museum-Australian Age of Dinosaurs project.

Evolutionary relationships

Diamantinasaurus is interpreted as a lithostrotian, a group of titanosaurs characterised by the presence of bony osteoderms in the skin (‘litho’ meaning ‘stone’, and ‘strotia’ referring to skin). Lithostrotians tended to be comparatively small forms, in contrast to most other titanosaurs, the largest land animals known to have lived. Huge sauropods - probably titanosaurs – lived in Australia during the Cretaceous, evidenced by footprints left along the Broome coastline (the largest of which is 1.5 metres across) in Western Australia (Thulborn et al. 1994).

References

• Coombs, W. P. Jr. and Molnar, R. E., 1981. Sauropods (Reptilia, Saurischia) from the Cretaceous of Queensland. Memoirs of the Queensland Museum 20, 351-373.
• Curry Rogers, K. 2005. Titanosauria: a phylogenetic overview. In: Curry Rogers, K., Wilson, J. A. (eds) The Sauropods: Evolution and Paleobiology. University of California Press, Berkeley and Los Angeles, pp. 50-103.
• Hocknull, S. A., White, M. A., Tischler, T. R., Cook, A. G., Calleja, N. D., Sloan, T. and Elliott, D. A., 2009. New mid-Cretaceous (latest Albian) dinosaurs from Winton, Queensland, Australia. PloS One 4(7), e6190.
• Longman, H. A., 1933. A new dinosaur from the Queensland Cretaceous. Memoirs of the Queensland Museum 13, 133-144.
• Molnar, R. E., 2000. A reassessment of the phylogenetic position of Cretaceous sauropods dinosaurs from Queensland, Australia. pp. 139-144 in Leanza, H. A. (ed) VII International Symposium of Terrestrial Ecosystems. Asociacion Paleontologica Argentina Publicacion Especial No. 7 Buenos Aires: Asociacion Paleontologica Argentina.
• Molnar, R. E. and Salisbury, S. W., 2005.
• Salgado, L., Calvo, J. L., Coria, R. A., 1997. Evolution of the titanosauriform sauropods. I. Phylogenetic evidence based on the postcranial evidence. Ameghiniana 34, 3-32.
• Thulborn, R. A. and Wade, M., 1984. Dinosaur trackways in the Winton Formation (mid-Cretaceous) of Queensland. Memoirs of the Queensland Museum 21, 413-517.
• Thulborn et al 94
• Upchurch, P., Barrett, P. M. and Dodson, P., 2004. Chapter 13: Sauropoda, in The Dinosauria, Second Edition (eds D. B. Weishampel, P. Dodson and H. Osmólska). University of California Press, Berkeley. Pp. 259-322.
• Wilson, J. A., 2002. Sauropod dinosaur phylogeny: critique and cladistic analysis. Zoological Journal of the Linnean Society 136, 217-276.

Further reading

• Long, J. A. et al. 2002. Dinosaurs of Australia and New Zealand and Other Animals of the Mesozoic Era. New South Wales University Press, Sydney.
• Salisbury, S. W., 2002. A giant awakes. Australian Geographic 65, 100-105.
• Salisbury, S. W., 2003a. Clash of the titans: the world’s largest dinosaurs. Nature Australia 27(7), 44-51.
• K. Curry Rogers and J. Wilson (eds). 2005. The Sauropods – Evolution and Paleobiology. University of California Press, Berkeley.
• V. Tidwell and K. Carpenter (eds). 2005. Thunder-Lizards: The Sauropodomorph Dinosaurs. Indiana University Press, Bloomington.