Diamantinasaurus
A medium-sized titanosaurian sauropod from Cretaceous Australia.
Diamantinasaurus is a genus of titanosaurian sauropod from Australia that lived during the early Late Cretaceous, about 94 million years ago. The type species, D. matildae, was named in 2009 based on fossils from the Winton Formation. Its name references the nearby Diamantina River and the Australian song 'Waltzing Matilda'.
Quick Facts
- Species
- matildae
Facts from the source article.
History of discovery
The dinosaur Diamantinasaurus was named in 2009 by Scott Hocknull and his team. Its scientific name comes from the nearby Diamantina River and the Greek word for lizard, while the species name honors the song "Waltzing Matilda," written in Winton by Banjo Paterson. The main specimen, labeled AODF 0603, includes a right shoulder blade, both upper arm bones, a right forearm bone, both incomplete hands, ribs and belly ribs, part of the pelvis, and the right hind leg without its foot. A second set of bones from the same animal, called the paratype, includes back and hip vertebrae, a bone now thought to be part of a coracoid, a radius, and one finger bone. These fossils were dug up over four seasons at the Matilda Site on Elderslie Sheep Station, about 60 kilometers west-northwest of Winton in central Queensland. The site lies in the upper middle part of the Winton Formation, which dates to the Cenomanian stage of the Late Cretaceous. The discovery ended a 75-year gap without a new Australian sauropod and was the largest dinosaur find in the country since Muttaburrasaurus in 1981. The holotype was found alongside the predator Australovenator, as well as crocodile relatives and mollusks.
Description
Diamantinasaurus was a medium-sized titanosaurian, measuring 16 m long and weighing up to 25 t. Like other sauropods, it was a large quadrupedal herbivore. Revisions since the original description include the misidentification of the 'sternal plate', misplacement of manual phalanges, and identification of a missing portion of the fibula. Before 2023, the skull was incompletely known, with only the posterior skull roof and braincase preserved. It shared traits with Saltasaurus and Rapetosaurus, including a frontal bone bordering the naris and a low ridge above the cranial foramen. In 2023, specimen AODF 0906 preserved a more complete skull about 50 cm long, referred to Diamantinasaurus based on nearly identical parietal, prootic, and surangular bones. The skull shape was more similar to brachiosaurids than derived titanosaurs and resembled that of Sarmientosaurus, confirming a close phylogenetic relationship. The left premaxilla preserved four tooth positions and five compressed cone-chisel-shaped replacement teeth, nearly identical to other teeth from the formation. No loose or active teeth were reported; the absence of maxillary processes on the premaxilla may be genuine or due to loss.
Classification
Originally assigned to Lithostrotia incertae sedis, Diamantinasaurus was placed either just outside Saltasauridae or as the sister taxon of Opisthocoelicaudia. A 2014 study found it as a lithostrotian in a relatively derived position within Titanosauria, with one phylogeny placing it as sister to Tapuiasaurus outside Saltasauridae, and another as a saltasaurid sister to Opisthocoelicaudia. A 2016 analysis recovered it as a non-lithostrotian titanosaur and sister to Savannasaurus. In 2019, a parsimony analysis placed it as a saltasaurid, while a Bayesian analysis placed it just outside Saltasauridae. A 2021 study found a close relationship with Savannasaurus and Sarmientosaurus, forming a clade dubbed Diamantinasauria. Beeston et al. (2024) considered Australotitan a junior synonym of Diamantinasaurus or an indeterminate diamantinasaurian, as its holotype lacks autapomorphic features and shares many similarities with known Diamantinasaurus specimens.
Paleobiology
In 2011, the smallest positively identified titanosaur embryo was described from Mongolia, sharing the most features with Diamantinasaurus and Rapetosaurus. The embryo, from a spherical egg 87.07–91.1 mm in diameter, was identified as a lithostrotian and was intermediate in robustness between the two genera. The egg is part of a nesting site for lithostrotian titanosaurs, predating those of Auca Mahuevo in Argentina. In 2025, fossilized gut contents from referred subadult specimen AODF 0888 provided direct dietary evidence of bulk feeding and multi-level browsing, including conifers, seed ferns, and flowering plants. The completeness of plant material indicated minimal oral processing, relying on fermentation and gut microflora for digestion. Three shed megaraptorid theropod teeth associated with the carcass suggested partial scavenging before burial.
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