Diamantinasaurus is a genus of titanosaurian sauropod from Australia that lived during the early Late Cretaceous, about 94 million years ago. The type species of the genus is D. matildae, first described and named in 2009 by Scott Hocknull and colleagues based on fossil finds in the Winton Formation. Meaning "Diamantina lizard", the name is derived from the location of the nearby Diamantina River and the Greek word sauros, "lizard". The specific epithet is from the Australian song Waltzing Matilda, also the locality of the holotype and paratype. The known skeleton includes most of the forelimb, shoulder girdle, pelvis, hindlimb and ribs of the holotype, and one shoulder bone, a radius and some vertebrae of the paratype.
History of discovery
The holotype of Diamantinasaurus was first uncovered over four seasons of excavations near Winton, Queensland, Australia. The bones were found alongside the holotype of Australovenator and crocodylomorphs and molluscs. The two dinosaurs found, known from specimens catalogued as AODF 0603 and 0604 were described in 2009 by Scott Hocknull and his colleagues. Specimen AODF 0603 became the basis for the genus Diamantinasaurus, and the species D. matildae. The species name is a reference to the song "Waltzing Matilda", written by Banjo Paterson in Winton, while the generic name is derived from the Diamantina River, running nearby the type locality combined with the Greek sauros, meaning "lizard". AODF 0603, the holotype, includes the right scapula, both humeri, right ulna, both incomplete hands, dorsal ribs and gastralia, partial pelvis, and the right hindlimb missing the foot. The paratype, under the same specimen, includes dorsal and sacral vertebrae, the right sternal plate now thought to represent the remainder of a coracoid, a radius, and one manual phalanx. All these bones come from AODL 85, nicknamed the "Matilda Site" at Elderslie Sheep Station, located about west-northwest from Winton in central Queensland. This locality is in the upper midsection of the Winton Formation, which dates to the Cenomanian of the Late Cretaceous.
The discovery of Diamantinasaurus ended a pause in the discovery of new dinosaurs in Australia, as the first sauropod named in over 75 years. Along with Australovenator, the holotype of Diamantinasaurus has been nicknamed after the Australian song "Waltzing Matilda", with Australovenator being called "Banjo" and Diamantinasaurus being nicknamed "Matilda". Wintonotitan, also from the site, was dubbed "Clancy". The find was apparently the largest dinosaur discovery in Australia that was documented since that of Muttaburrasaurus in 1981.
As of 2025, additional specimens have been described since its initial description, with each specimen being nicknamed as the following: "Alex" for AODF 0836, "Oliver" for AODF 0663, "Ann" for AODF 0906, "Devil Dave" for AODF 0666, "Ian" for AODF 0844 and "Judy" for AODF 0888. The second specimen, AODF 0836, was first described in 2016. It includes portions of the skull, including a left squamosal, nearly complete braincase, right surangular, and various fragments. Additionally, the specimen also includes the atlas, axis, five other cervical vertebrae, three dorsal vertebrae, additional dorsal ribs, portions of the hip, and another right scapula. In 2021, this referred material was thoroughly described. In 2022, the right dentary fragment with teeth and isolated tooth crown was referred to AODF 0603, while the isolated tooth, AODF 2298, was tentatively suggested to be part of the same individual as AODF 0836. In the same year, the third specimen, AODF 663, was referred to as a juvenile specimen. In 2023, the fourth specimen, AODF 0906, consisting of a partial postcranial skeleton and a more complete skull with previously unknown numerous cranial elements intact has been described in detail. In 2024, the fifth and sixth specimen, AODF 0666 and AODF 0844, consisting of the incomplete hindlimb and scapulocoracoid respectively have been described. In 2025, the seventh specimen, AODF 0888, consisting of a partial cranial and postcranial skeleton with the first known fossilized gut content among all sauropods and the skin preserving polygonal (mostly hexagonal) scales has been described.
Description
Diamantinasaurus was a medium-sized titanosaurian, measuring long and weighing up to . Genus List for Holtz 2012 Weight Information Like other sauropods, Diamantinasaurus would have been a large quadrupedal herbivore. Since the original description, the only major revisions include the misidentification of the "sternal plate", misplacement of manual phalanges III-1 and IV-1 as III-1 and V-1 respectively, and the identification of the missing portion of the fibula.
Skull Before 2023, the skull of Diamantinasaurus was incompletely known like most other titanosaurs, with only the posterior skull roof and braincase being preserved. Similarly to Saltasaurus and Rapetosaurus and unlike Nemegtosaurus, the was bordered by the frontal bone. Contrasting from both latter genera, Diamantinasaurus has a low above the cranial foramen, which is subsequently less than 1.5 times the height of the (which has a foramen). All of these traits are however shared with Saltasaurus. Multiple other traits are found throughout derived titanosaurs, including downward angling of the skull, prong shaped lateral braincase processes, an undisturbed pituitary fossa, and a more centrally located opening for the internal carotid artery.
In 2023, Poropat and colleagues described a new specimen AODF 0906, which preserved the more complete skull with an estimated total length of approximately . The referral of this specimen to Diamantinasaurus is supported by some of the nearly identical structures including the parietal, prootic and surangular when compared to AODF 0836. The skull was overall more similar in shape to that of brachiosaurids than derived titanosaurs, and it had similar features to those on the known cranial material of the Argentinian titanosaur Sarmientosaurus which confirmed their previously assumed close phylogenetic relationship. The left premaxilla of the skull preserved four tooth positions and five compressed cone-chisel-shaped replacement teeth, with the latter being nearly identical to other teeth material from the same formation previously attributed to this taxon. No loose teeth or active teeth were reported from this skull. The absence of maxillary processes on the premaxilla could be either a genuine trait or a lost part of the specimen.
Vertebrae As is typical for Titanosauriformes, all cervical and dorsal vertebrae of Diamantinasaurus are and camellate (many small internal chambers). The axis vertebra of the genus is short, a potential characteristic of Saltasauridae. Contrasting Saltasaurus and Rapetosaurus however, the of Diamantinasaurus extend in front of the centrum. Only certain in the known middle dorsals, the (ridge on posterior surface of spine) extends below the spine itself. Like more basal sauropods Europasaurus and Euhelopus, the dorsal vertebrae have a notch on the top of the posterior centrum face, giving it a heart-shaped appearance, contrasting more derived titanosaurs or Giraffatitan which possess flattened centra. Although differing in centrum shape, Opisthocoelicaudia and Diamantinasaurus are the only titanosaurs to share a ventral keel set within a sharply defined depression under the dorsals. Dorsal prezygapophyses are linked to the spine by a , which is absent in Opisthocoelicaudia and most dorsals of Rapetosaurus, and the found in Diamantinasaurus is also absent in most derived titanosaurs. There is no indication of a , a diagnostic feature of derived titanosaurs. Shared with Opisthocoelicaudia, Alamosaurus and Lirainosaurus to the exclusion of other titanosaurs, Diamantinasaurus has a simple undivided ridge between the posterior centrum and diapophysis (). A poorly preserved feature between the prezygapophysis and centrum may be the , found in some brachiosaurids, basal titanosaurs, and Opisthocoelicaudia. Diamantinasaurus possessed at least five, possibly six, sacral vertebrae.
Forelimb
Almost all the right forelimb is known from Diamantinasaurus, although the left humerus is known in addition to the right, and the left first metacarpal is known while the right is unpreserved. Diagnostic of Diamantinasaurus, the glenoid (humerus) articulation of the scapula is rotated to the outside, differing from all other somphospondylans. Similar to Alamosaurus and taxa around the base of Titanosauria, at least a single ventral process is known, although it is poorly preserved. The scapula of Diamantinasaurus is robust, having a more round cross-section than other somphospondylans. The coracoid, misidentified as a sternal in the original description, is plain and unfeatured, contrasting Huabeisaurus, Lirainosaurus and Opisthocoelicaudia. The proximal surface of the humerus is prominently curved as in the derived titanosaurs Opisthocoelicaudia and Saltasaurus. The lateral corner is also squared, placing it within Somphospondyli. Like with most somphospondylans but unlike Euhelopus and Rapetosaurus, Diamantinasaurus has a middle-shifted . Ridges for muscle attachment are less developed than in Opisthocoelicaudia and Magyarosaurus. Differing from derived titanosaurs, the condyles to articulate with the forearm are not pronounced. Diamantinasaurus has an ulna comparing to derived titanosaurs in the level of robustness, as well as having a very pronounced olecranon. Similarly, the radius of Diamantinasaurus is more robust than all titanosaurs except Opisthocoelicaudia. The ulna is long, while the radius is .
Because of the completeness of the forelimb material, the absence of carpal bones among the preserved material was presumed by Poropat et al. (2014) to be related to their genuine absence in life, as in Opisthocoelicaudia and Alamosaurus. The manus of Diamantinasaurus comparatively displays some plesiomorphic features, including: the middle metacarpal being the longest ( Mc III compared to next longest Mc II); the presence of a thumb claw; and the presence of multiple phalanges, having the phalangeal formula 2–1–1–1–1. However, the manus of Diamantinasaurus is completely cylindrical and vertical like other titanosaurs. The presence of large numbers of phalanges in Diamantinasaurus was used by Poropat et al. (2014) to suggest that all titanosaurs actually had ossified phalanges contrasting earlier studies. Following this logic, they suggested that for Opisthocoelicaudia and Epachthosaurus, which both preserve a single phalanx from the fourth finger, the absence of others was due to them being lost before fossilization for the preceding digits, instead of absence. The complete absence of preserved phalanges in Alamosaurus, Rapetosaurus, Neuquensaurus and Saltasaurus potentially being due to disarticulation instead of absence of ossification.
Hindlimb