Tuesday, December 8, 2015

[Paleontology • 2015] Kunbarrasaurus ieversi • Cranial Osteology of the Ankylosaurian Dinosaur formerly known as ''Minmi'' sp. (Ornithischia: Thyreophora) from the Lower Cretaceous Allaru Mudstone of Richmond, Queensland, Australia

Kunbarrasaurus ieversi
Leahey, Molnar, Carpenter, Witmer & Salisbury, 2015

Minmi is the only known genus of ankylosaurian dinosaur from Australia. Seven specimens are known, all from the Lower Cretaceous of Queensland. Only two of these have been described in any detail: the holotype specimen Minmi paravertebra from the Bungil Formation near Roma, and a near complete skeleton from the Allaru Mudstone on Marathon Station near Richmond, preliminarily referred to a possible new species of Minmi. The Marathon specimen represents one of the world’s most complete ankylosaurian skeletons and the best-preserved dinosaurian fossil from eastern Gondwana. Moreover, among ankylosaurians, its skull is one of only a few in which the majority of sutures have not been obliterated by dermal ossifications or surface remodelling. Recent preparation of the Marathon specimen has revealed new details of the palate and narial regions, permitting a comprehensive description and thus providing new insights cranial osteology of a basal ankylosaurian. The skull has also undergone computed tomography, digital segmentation and 3D computer visualisation enabling the reconstruction of its nasal cavity and endocranium. The airways of the Marathon specimen are more complicated than non-ankylosaurian dinosaurs but less so than derived ankylosaurians. The cranial (brain) endocast is superficially similar to those of other ankylosaurians but is strongly divergent in many important respects. The inner ear is extremely large and unlike that of any dinosaur yet known. Based on a high number of diagnostic differences between the skull of the Marathon specimen and other ankylosaurians, we consider it prudent to assign this specimen to a new genus and species of ankylosaurian. Kunbarrasaurus ieversi gen. et sp. nov. represents the second genus of ankylosaurian from Australia and is characterised by an unusual melange of both primitive and derived characters, shedding new light on the evolution of the ankylosaurian skull.

Keywords: Dinosauria, Thyreophora, Eurypoda, Ankylosauria, Gondwana, Computed tomography, Nasal cavity, Braincase

The holotype skeleton of Kunbarrasaurus ieversi (QM F18101), Australia’s most complete dinosaur fossil, and one of the world’s most complete ankylosaurians.
image: Anthony O’Toole and Lucy Leahey

Dinosauria Owen, 1842
Ornithischia Seeley, 1888

Thyreophora Nopcsa, 1915
Eurypoda Sereno, 1986

Ankylosauria Osborn, 1923

Kunbarrasaurus ieversi gen. et sp. nov.
(formerly Minmi sp. Molnar, 1996a)

Etymology. The generic name combines Kunbarra [kunbara], the Mayi (Wunumara) word for ‘shield’, and souros (σ αυρoς), the Greek word for ‘lizard’, and is a reference to the animal’s heavily ossified skin. The species name honours Mr Ian Ievers, discoverer of the holotype. The name therefore means ‘Ievers’ shield-lizard’.

Holotype. QM F18101, a near-complete ankylosaurian dinosaur specimen that includes most of the skull and mandible, along with an articulated postcranium.

The assignment of a new genus and species name Kunbarrasaurus ieversi to QM F18101 (formerly known as Minmi sp.) is based on a significant number of features that distinguish it from other ankylosaurians. Many of the cranial sutures of K. ieversi have not fused, nor are they obscured by dermal ossifications. The closure of the antorbital and supratemporal fenestrae of K. ieversi is most likely due to the expansion of cranial bones, and not the result of overgrowth of dermal ossifications. The ornamentation of the skull of K. ieversi is the result of both epidermal ossification (osteoderms) and periosteal osteogenesis. Some aspects of the nasal cavity remain obscure, but there is enough evidence to suggest that K. ieversi had a more complicated airway than in non-ankylosaurian outgroups. It is presently unclear whether K. ieversi had a convoluted, looping nasal passage to the extent seen in more advanced ankylosaurians. Some aspects of the braincase are potentially unique among known species, such as the unusual inner ear, which is not only extremely large but also has a divergent morphology due to lack of ossification medially and ventrally.

Lucy G. Leahey, Ralph E. Molnar, Kenneth Carpenter, Lawrence M. Witmer and Steven W. Salisbury. 2015. Cranial Osteology of the Ankylosaurian Dinosaur formerly known as ''Minmi'' sp. (Ornithischia: Thyreophora) from the Lower Cretaceous Allaru Mudstone of Richmond, Queensland, Australia. PeerJ.  3; e1475. doi: 10.7717/peerj.1475

Kunbarrasaurus is Australia’s new armoured dinosaur - Australian Geographic http://www.australiangeographic.com.au/blogs/austropalaeo/2015/12/kunbarrasaurus-is-australia%E2%80%99s-new-armoured-dinosaur via @john_pickrell @AusGeo
Australia's new armoured dinosaur revealed http://phy.so/368778074 via @physorg_com