| Diamantinasaurus | |
|---|---|
 | |
| Holotype skeleton in (a) right and (b) left views | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Sauropoda |
| Clade: | †Macronaria |
| Clade: | †Somphospondyli |
| Clade: | †Diamantinasauria |
| Genus: | †Diamantinasaurus Hocknull et al.,2009 |
| Species: | †D. matildae |
| Binomial name | |
| †Diamantinasaurus matildae Hocknull et al., 2009 | |
Diamantinasaurus is a genus oftitanosauriansauropod fromAustralia that lived during the earlyLate Cretaceous, about 94 million years ago. Thetype species of the genus isD. matildae, first described and named in2009 byScott Hocknull and colleagues based on fossil finds in theWinton Formation. Meaning "Diamantina lizard", the name is derived from the location of the nearbyDiamantina River and theGreek wordsauros, "lizard". The specific epithet is from theAustralian songWaltzing Matilda, also thelocality of theholotype andparatype. The known skeleton includes most of theforelimb,shoulder girdle,pelvis,hindlimb andribs of the holotype, and one shoulder bone, aradius and somevertebrae of the paratype.
Theholotype ofDiamantinasaurus was first uncovered over four seasons of excavations nearWinton, Queensland, Australia. The bones were found alongside the holotype ofAustralovenator andcrocodylomorphs andmolluscs.[1] The two dinosaurs found, known from specimens catalogued asAODF 0603 and 0604 were described in 2009 byScott Hocknull and his colleagues. Specimen AODF 0603 became the basis for the genusDiamantinasaurus, and the speciesD. matildae. The species name is a reference to the song "Waltzing Matilda", written byBanjo Paterson in Winton, while the generic name is derived from theDiamantina River, running nearby the type locality combined with theGreeksauros, meaning "lizard". AODF 0603, theholotype, includes the rightscapula, bothhumeri, rightulna, both incompletehands, dorsalribs andgastralia, partialpelvis, and the right hindlimb missing the foot.[3] Theparatype, under the same specimen, includes dorsal and sacral vertebrae, the right sternal plate now thought to represent the remainder of acoracoid, aradius, and one manualphalanx. All these bones come from AODL 85, nicknamed the "Matilda Site" atElderslie Sheep Station, located about 60 km (37 mi) west-northwest from Winton in centralQueensland. This locality is in the upper midsection of theWinton Formation, which dates to theCenomanian of theLate Cretaceous.[1][3]
The discovery ofDiamantinasaurus ended a pause in the discovery of new dinosaurs in Australia, as the first sauropod named in over 75 years. Along withAustralovenator, the holotype ofDiamantinasaurus has been nicknamed after the Australian song "Waltzing Matilda", withAustralovenator being called "Banjo" andDiamantinasaurus being nicknamed "Matilda".Wintonotitan, also from the site, was dubbed "Clancy".[4][5] The find was apparently the largest dinosaur discovery in Australia that was documented since that ofMuttaburrasaurus in 1981.[5]
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.[6][7] The second specimen, AODF 0836, was first described in 2016. It includes portions of the skull, including a leftsquamosal, nearly completebraincase, rightsurangular, and various fragments. Additionally, the specimen also includes theatlas,axis, five other cervical vertebrae, three dorsal vertebrae, additional dorsal ribs, portions of the hip, and another right scapula.[8] In 2021, this referred material was thoroughly described.[9] 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.[10] In the same year, the third specimen, AODF 663, was referred to as a juvenile specimen.[11] 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.[12] In 2024, the fifth and sixth specimen, AODF 0666 and AODF 0844, consisting of the incomplete hindlimb and scapulocoracoid respectively have been described.[6] 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.[7]
Diamantinasaurus was a medium-sized titanosaurian, measuring 16 m (52 ft) long and weighing up to 25 t (28 short tons).[13][14] Like other sauropods,Diamantinasaurus would have been a largequadrupedalherbivore.[15] 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.[1]
Before 2023, the skull ofDiamantinasaurus was incompletely known like most other titanosaurs, with only the posterior skull roof and braincase being preserved. Similarly toSaltasaurus andRapetosaurus and unlikeNemegtosaurus, thesupratemporal fenestra was bordered by thefrontal bone. Contrasting from both latter genera,Diamantinasaurus has a lowsupraoccipital above the cranial foramen, which is subsequently less than 1.5 times the height of thebasal tuberae (which has a foramen). All of these traits are however shared withSaltasaurus. Multiple other traits are found throughout derived titanosaurs, including downward angling of the skull, prong shaped lateral braincase processes, an undisturbedpituitary fossa, and a more centrally located opening for theinternal carotid artery.[8]
In 2023, Poropat and colleagues described a new specimen AODF 0906, which preserved the more complete skull with an estimated total length of approximately 50 centimetres (20 in). The referral of this specimen toDiamantinasaurus 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 titanosaurSarmientosaurus which confirmed their previously assumed close phylogenetic relationship. The leftpremaxilla 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 ofmaxillary processes on the premaxilla could be either a genuine trait or a lost part of the specimen.[12]
As is typical forTitanosauriformes, all cervical and dorsal vertebrae ofDiamantinasaurus areopisthocoelous and camellate (many small internal chambers). Theaxis vertebra of the genus is short, a potential characteristic ofSaltasauridae. ContrastingSaltasaurus andRapetosaurus however, theprezygapophyses ofDiamantinasaurus extend in front of the centrum. Only certain in the known middle dorsals, thepostspinal lamina (ridge on posterior surface of spine) extends below the spine itself.[8] Like more basal sauropodsEuropasaurus andEuhelopus, the dorsal vertebrae have a notch on the top of the posterior centrum face, giving it a heart-shaped appearance, contrasting more derived titanosaurs orGiraffatitan which possess flattened centra. Although differing in centrum shape,Opisthocoelicaudia andDiamantinasaurus 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 aspinoprezygapophyseal lamina, which is absent inOpisthocoelicaudia and most dorsals ofRapetosaurus, and thepostzygodiapophyseal lamina found inDiamantinasaurus is also absent in most derived titanosaurs. There is no indication of ahyposphene-hypantrum articulation, a diagnostic feature of derived titanosaurs. Shared withOpisthocoelicaudia,Alamosaurus andLirainosaurus to the exclusion of other titanosaurs,Diamantinasaurus has a simple undivided ridge between the posterior centrum and diapophysis (posterior centrodiapophyseal lamina). A poorly preserved feature between the prezygapophysis and centrum may be theposterior centroprezygapophyseal lamina, found in some brachiosaurids, basal titanosaurs, andOpisthocoelicaudia.Diamantinasaurus possessed at least five, possibly six,sacral vertebrae.[1]
Almost all the right forelimb is known fromDiamantinasaurus, although the left humerus is known in addition to the right, and the left first metacarpal is known while the right is unpreserved. Diagnostic ofDiamantinasaurus, theglenoid (humerus) articulation of the scapula is rotated to the outside, differing from all other somphospondylans. Similar toAlamosaurus and taxa around the base of Titanosauria, at least a single ventral process is known, although it is poorly preserved. Thescapula ofDiamantinasaurus 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, contrastingHuabeisaurus,Lirainosaurus andOpisthocoelicaudia. Theproximal surface of the 1.068 m (3.50 ft) humerus is prominently curved as in the derived titanosaursOpisthocoelicaudia andSaltasaurus. The lateral corner is also squared, placing it within Somphospondyli. Like with most somphospondylans but unlikeEuhelopus andRapetosaurus,Diamantinasaurus has a middle-shifteddeltopectoral crest. Ridges for muscle attachment are less developed than inOpisthocoelicaudia andMagyarosaurus. 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 pronouncedolecranon. Similarly, the radius ofDiamantinasaurus is more robust than all titanosaurs exceptOpisthocoelicaudia. The ulna is 70 cm (28 in) long, while the radius is 67.5 cm (26.6 in).[1]
Because of the completeness of the forelimb material, the absence ofcarpal bones among the preserved material was presumed by Poropat et al. (2014) to be related to their genuine absence in life, as inOpisthocoelicaudia andAlamosaurus. The manus ofDiamantinasaurus comparatively displays some plesiomorphic features, including: the middlemetacarpal being the longest (41.2 cm (16.2 in) Mc III compared to next longest 37.5 cm (14.8 in) 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 ofDiamantinasaurus is completely cylindrical and vertical like other titanosaurs. The presence of large numbers of phalanges inDiamantinasaurus 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 forOpisthocoelicaudia andEpachthosaurus, 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 inAlamosaurus,Rapetosaurus,Neuquensaurus andSaltasaurus potentially being due to disarticulation instead of absence of ossification.[1]
The leftilium, left and rightpubes, left and rightischia, and entire right leg lacking the foot are preserved forDiamantinasaurus, although some bones are highly fragmented and poorly preserved. The ilium has the outside well preserved, but its size and fragility mean the internal side cannot be seen for anatomical features. The top edge of the ilium is broken, revealing numerous small internal camerae, as present in the titanosaursAlamosaurus,Epachthosaurus,Lirainosaurus,Saltasaurus andSonidosaurus. Shared with other derived titanosaurs, the anterior process of the ilium flares to the side and rotates so the vertical ilium body becomes a horizontal shelf.Diamantinasaurus also displays the derived sauropod traits of a rounded ilium, reduced articular surface for the ischium, and a protuberance above the ischiatic articulation (only shared withOpisthocoelicaudia among Titanosauriformes). The pubis, as in advanced sauropods, is a flattened bone, lacking the anterior hook of diplodocoids, but with potentially autapomorphic grooves surrounding theobturator foramen. Articulation with the ischium takes up 46% of the pubic length, as in most macronarians but contrasting withAlamosaurus andOpisthocoelicaudia, where it is reduced. The entire ischium is only 68% of the length of the pubis as in other titanosaurs, and also expands medially so the entire floor of the pelvis is closed. Unlike some titanosaurs, the ischium ofDiamantinasaurus displays no constriction of its width, nor a flange projecting internally.Diamantinasaurus also lacks a notable muscle scar for theM. flexor tibialis internus 3 on the side of the distal ischium, which is diagnostic for the taxon amongstNeosauropoda.[1]
The femur, 1.345 m (4.41 ft) long, is roughly twice as wide as it is long, as in other derived sauropods, although it has been slightly crushed. The crushing did not prevent the preservation of thelinea intermuscularis cranialis ridge, also present inSaltasaurus,Neuquensaurus,Bonatitan,Rocasaurus andAlamosaurus. As is typical for a sauropod, the head of the femur is slightly above thegreater trochanter, and there is a mild trochanteric shelf. A moderate lateral bulge is present, above which the femur is shifted medially, like most macronarians exceptOpisthocoelicaudia,Saltasaurus andRapetosaurus. The condyles for articulation with thetibia andfibula extend high onto the posterior surface of the femur, but unlikeNeuquensaurus andOpisthocoelicaudia do not extend onto the anterior surface. A depression subdivides the fibular condyle, which bears a slight ridge also found inMagyarosaurus and other titanosaurs, although the prominence of it is unique toDiamantinasaurus. The fibular condyle is larger than the tibial, and extends farther down, giving the femur a bevelled appearance, potentially diagnostic of Saltasauridae but also found inRapetosaurus and the non-titanosaurDongbeititan.[1]
The tibia is 59% of the length of the femur, and as is normal for neosauropods is wider than it is long on the proximal surface.Diamantinasaurus bears multiple fossae and ridges on the tibia that have not been observed in other sauropods, making them a suite of diagnostic traits. As in many titanosaurs, the distal end of the tibia is flared to over double the midshaft width, although a thin flange along the midshaft may be diagnostic toDiamantinasaurus. Originally reconstructed missing part of the shaft, the fibula is 76.9 cm (30.3 in) long, and is intermediately robust, although close to gracile. The bone is poorly preserved, but still displays a diagnostic widening of the fibular muscle scar, and a diagnostic medial ridge with surrounding grooves. As in many titanosauriforms, theastragalus ofDiamantinasaurus is less than 1.5 times as wide as long, and the proximal surface is divided into the ascending process and the fossa for the tibia. There is also a shallow fossa for the fibula on the outside face of the astragalus, giving the bone a subtriangular shape. No depressions or foramina are present at the anterior base of the ascending process, a condition typical ofEusauropoda. A process on the posterior side of the astragalar body is unique among all sauropods, making it an autapomorphy ofDiamantinasaurus.[1]
When it was originally described,Diamantinasaurus was assigned to Lithostrotiaincertae sedis. In both phylogenies it was placed in,Diamantinasaurus was either just outsideSaltasauridae or the sister taxon ofOpisthocoelicaudia within the family.[3] In a 2014 study, it was found that the genus was placed as a lithostrotian in both large phylogenies, in a relatively derived position in Titanosauria. Their first phylogeny was modified from that of Carbadillo and Sander (2014), the matrix being indirectly based on Wilson's 2002 phylogeny. In that cladogram,Diamantinasaurus was found to be sister taxon toTapuiasaurus, their relationship outside ofSaltasauridae. In this phylogeny, the Bremer support for each group was at most 1. Five features of the skeleton supported the placement ofDiamantinasaurus in Lithostrotia.[1]
In the same study, the relationships using the Mannion et al. (2013) matrix were tested. These resolved withDiamantinasaurus as a saltasaurid, sister toOpisthocoelicaudia, withDongyangosaurus as the next closest. Two characters were found to support the placement ofDiamantinasaurus in Lithostrotia, and a third could not be evaluated.[1]
Another phylogenetic analysis in 2016, partially reproduced below, found it as a non-lithostrotian titanosaur and the sister taxon of the contemporarySavannasaurus.[8][16]
Gorscak & O'Connor (2019) in their description ofMnyamawamtuka recoveredDiamantinasaurus as a saltasaurid using a parsimony phylogenetic analysis, while a variable-rates Bayesian phylogenetic analysis recovered it as falling just outside Saltasauridae.[17]
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The 2021 study recovered a similar topology, finding a close relationship withSavannasaurus as well asSarmientosaurus from the early Late Cretaceous of Patagonia, which skull had similarities to the referred cranial material ofDiamantinasaurus. The clade containing these taxa was dubbedDiamantinasauria.[9] Beeston et al. (2024) consideredAustralotitan as a junior synonym ofDiamantinasaurus or an indeterminate species of diamantinasaurian titanosaur, since the holotype ofAustralotitan possesses no distinguishable autapomorphic features to classify it as a valid genus and shares many similarities with known specimens ofDiamantinasaurus.[6]
In 2011, the smallest positively identified titanosaur embryo was described. Although it was uncovered inMongolia, the embryo shares the most features withDiamantinasaurus andRapetosaurus. The embryo, from a relatively spherical 87.07–91.1 millimetres (3.428–3.587 in) egg, was identified as persisting to a lithostrotian. The embryo was slightly robust, intermediate between the robustness ofRapetosaurus andDiamantinasaurus. The egg is part of an entire nesting site for lithostrotian titanosaurs. Dating of the region also suggests that this egg predates those ofAuca Mahuevo in Argentina, and that the eggs were laid in theEarly Cretaceous.[18]
In 2025, the fossilized gut contents from a referred subadult specimen AODF 0888 was described in detail.[7] Prior to this discovery, the gut contents of sauropods have never been reported, so the exact diet of sauropods had to be largely speculated.[19] The specimen provided direct dietary evidence of bulk feeding and multi-level browsing, resulting in consumption of conifers, seed ferns and flowering plants. The relative completeness of the plant material also indicated that sauropods used their mouths minimally to process their food and relied on "fermentation and their gut microflora for digestion". The association of three shedmegaraptorid theropod teeth suggested that the carcass might have been partially scavenged before burial.[7]
Diamantinasaurus was found about 60 kilometres (37 mi) northwest of Winton, near Elderslie Station.[3] It was recovered from the fossil-rich section of theWinton Formation, which can be dated to approximately 93 million years ago.[2]Diamantinasaurus was found in a clay layer betweensandstone layers, interpreted as anoxbow lake deposit. Also found at the site wasAustralovenator, which was directly associated withDiamantinasaurus,bivalves,fish,turtles,crocodilians, and variousplants. The Winton Formation had a faunal assemblage including bivalves,gastropods,insects, thelungfishMetaceratodus, turtles, thecrocodilianIsisfordia,pterosaurs, and several types of dinosaurs, such as the aforementionedAustralovenator, the sauropodsWintonotitan,Savannasaurus, andAustrosaurus, and unnamedankylosaurians andhypsilophodonts.Diamantinasaurus bones can be distinguished from other sauropods because of the overall robusticity as well as multiple specific features. Plants known from the formation includeferns,ginkgoes,gymnosperms, andangiosperms.[3]
