Diamantinasaurus matildae, a titanosaur recently discovered near Winton in central Queensland, is the most complete Australian sauropod known. Diamantinasaurus and a second titanosaur, Wintonotitan, are the first new sauropods described from Australia in over 75 years. The solidly-built Diamantinasaurus, about 15 metres in length, was 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 billabong.
Diamantinasaurus matildae was a titanosaur, a group of sauropods known mainly from Gondwanan continents. Titanosaurs, the largest terrestrial animals known, may have reached 35 metres in length and 100 tonnes in weight. Diamantinasaurus was a relatively small titanosaur, from15 to 16 metres in length and 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 Lithostrotia (‘Titanosauridae’ + Saltasauridae), titanosaurs characterized 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 (reconstruction by Travis Tischler, Age of Australian Dinosaurs Museum of Natural History), 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.
The Winton Formation is made up of sandstones, siltstones and claystones formed during the mid-Cretaceous Period (about 100 million years ago). At this time, the region was an extensive river plain filling the lowlands left behind by the retreating Eromanga Sea. The environment would have been a mosaic of large, winding rivers, freshwater pools, billabongs, swamps, lakes 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 and Wintonotitan are from the basal part of the Winton Formation, not far from the type locality of Lovellea wintonensis (an early flowering plant).
Diamantinasaurus comes from the Winton Formation of central Queensland, Australia, a huge formation spread across much of central Australia.
Feeding and diet
Sauropods were herbivores, based on features of the skull and teeth as well as on their massive body size. 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.
Diamantinasaurus is known from a complete front limb and shoulder girdle, ribs and possible gastralia; a complete pelvic girdle, and the upper hind limb. Although Diamantinasaurus has been reconstructed with osteoderms (characteristic of some Saltasauridae), these have not yet been found, and it is not known if Diamantinasaurushad these dermal bones.
Diamantinasaurus was found north-west of the town of Winton and east of the Diamantina River in Queensland along with the remains of Australovenator wintonensisin a low-energy channel fill deposit, possibly a billabong (ox-bow lake). 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.
Diamantinasaurus is interpreted as a lithostrotian, a group of titanosaurs characterized 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).
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