Tuesday, June 8, 2021

[Paleontology • 2021] Australotitan cooperensis • A New Giant Sauropod (Saurischia: Titanosauria) from the mid-Cretaceous of Australia

Australotitan cooperensis
Hocknull​, Wilkinson, Lawrence, Konstantinov, Mackenzie & Mackenzie, 2021

A new giant sauropod, Australotitan cooperensis gen. et sp. nov., represents the first record of dinosaurs from the southern-central Winton Formation of the Eromanga Basin, Australia. We estimate the type locality to be 270–300 m from the base of the Winton Formation and compare this to the semi-contemporaneous sauropod taxa, Diamantinasaurus matildae Hocknull et al., 2009, Wintonotitan wattsi Hocknull et al., 2009 and Savannasaurus elliottorum Poropat et al., 2016. The new titanosaurian is the largest dinosaur from Australia as represented by osteological remains and based on limb-size comparisons it reached a size similar to that of the giant titanosaurians from South America. Using 3-D surface scan models we compare features of the appendicular skeleton that differentiate Australotitan cooperensis gen. et sp. nov. as a new taxon. A key limitation to the study of sauropods is the inability to easily and directly compare specimens. Therefore, 3-D cybertypes have become a more standard way to undertake direct comparative assessments. Uncoloured, low resolution, and uncharacterized 3-D surface models can lead to misinterpretations, in particular identification of pre-, syn- and post-depositional distortion. We propose a method for identifying, documenting and illustrating these distortions directly onto the 3-D geometric surface of the models using a colour reference scheme. This new method is repeatable for researchers when observing and documenting specimens including taphonomic alterations and geometric differences. A detailed comparative and preliminary computational phylogenetic assessment supports a shared ancestry for all four Winton Formation taxa, albeit with limited statistical support. Palaeobiogeographical interpretations from these resultant phylogenetic hypotheses remain equivocal due to contrary Asian and South American relationships with the Australian taxa. Temporal and palaeoenvironmental differences between the northern and southern-central sauropod locations are considered to explain the taxonomic and morphological diversity of sauropods from the Winton Formation. Interpretations for this diversity are explored, including an eco-morphocline and/or chronocline across newly developed terrestrial environments as the basin fills.


Systematic Palaeontology

Dinosauria Owen, 1842
Saurischia Seeley, 1887

Sauropodomorpha von Huene, 1932
Sauropoda Marsh, 1878
Eusauropoda Upchurch, 1995
Neosauropoda Bonaparte, 1986
Macronaria Wilson and Sereno, 1998

Titanosauriformes Salgado et al., 1997a
Somphospondyli Wilson and Sereno, 1998
Titanosauria Bonaparte and Coria, 1993

Australotitan gen. nov.

Australotitan cooperensis gen. et sp. nov.

Material. Holotype: EMF102, consists of ten appendicular elements and pieces of corticocancellous internal bone. The appendicular elements include a partial left scapula, partial left and complete right humerus, right ulna, right and left pubes and ischia, and partial right and left femora.

Referred Specimens: EMF164, a fragmented femur, a fragmented ulna, presacral vertebral centrum fragments and rib fragments. EMF105, a complete femur and EMF165, a distal humerus.

Age & Horizon. Cenomanian-? Turonian, Winton Formation.

Type Locality. EML011(a). Referred Specimen Localities, EML010 & EML013.

Etymology. Australo–meaning southern in Greek and in reference to the southern continent of Australia; titan–from the Greek mythological Titan gods and in reference to its gigantic size; cooperensis–being from the Cooper-Eromanga Basin, Cooper Creek system & “Cooper Country”.

Diagnosis: A large titanosaurian sauropod with the following combination of characters that differentiate this new taxon from all others. Proposed autapomorphies indicated by an asterisk. Scapular blade, narrow and straight with sub-parallel dorsal and ventral margins with lateral ridge situated near the ventral margin. Humerus with a rounded ridge that extends from the distal end of the deltopectoral crest to just proximal of a tri-lobate distal epiphysis. Ulna with heavily reduced anterolateral and olecranon processes relative to much enlarged and elongate anteromedial process. Ulna with a distinct radial interosseous ridge within the distal half of the radial fossa*. Anterolateral process of the ulna with a distal accessory projection* proximal to a proximally beveled distal epiphysis*. Pubes and ischia broad and contact each other medially forming a cohesive pelvic floor. Distal ischial blades curve ventrally to produce a dorsal face that is posteriorly directed. Femur with a medially sloped proximolateral margin, diaphysis narrow anteroposteriorly, and distal condyles directed anterolaterally to posteromedially.

Scott A. Hocknull​, Melville Wilkinson, Rochelle A. Lawrence, Vladislav Konstantinov, Stuart Mackenzie and Robyn Mackenzie. 2021. A New Giant Sauropod, Australotitan cooperensis gen. et sp. nov., from the mid-Cretaceous of Australia. PeerJ. 9:e11317. DOI: 10.7717/peerj.11317