Monday 20 February 2012

New description of an Ankylosaurid Dinosaur from Mongolia.

The 1971 Polish-Mongolian Palaeontological Expedition to the Gobi Desert unearthed a great deal of dinosaurian material, including the partial skeleton of an Ankylosaurid Dinosaur, which was given the specimen number ZPAL MgD I/113 and referred to the genus Dyplosaurus, but not properly prepared or described. Ankylosauridd were armored Ornithischian Dinosaurs from the Cretaceous. They typically had a thick covering of fused boney plates that enclosed their torsos in a sort of shell, which could be adorned with a variety of spikes and lumps. They also had armored heads, with a beak-like mouth that had teeth only at the rear, and often had a fused, boney lump at the end of their tales, which apparently served as a weapon.

In 1998 the specimen was sent to the Geological Museum of Oslo for preparation and study, and it is formally described in a forthcoming paper in the journal Acta Palaeontologica Polonica by a team of scientists led by Victoria Arbour of the Department of Biological Sciences at the University of Alberta.

Part of the posterior of the trunk of specimen ZPAL MgD I/113, showing boney scutes and impressions of soft armor. Scale bar is 10 cm. From Arbour et al. (2012).

Arbour et al. assigned specimen ZPAL MgD I/113 to the species Tarchia gigantea (there is currently dispute as to whether Dyplosaurus is a valid taxon at all), an 8-8.5 m, 4.5 tonne (probably) Ankylosaurid well documented from a number of other Mongolian specimens.

Reconstruction of Tarchia gigantea by Mineo Shiraishi.

Although there are several more complete specimens of Tarchia gigantea in various museum collections, ZPAL MgD I/113 does show some features not previously seen in the species, notably impressions of the keratinous scales that overlaid the armor plates, and an almost complete tail, which reveals T. gigantea to have had the longest known tail of any Ankylosaurid Dinosaur.

Two blocks from ZPAL MgD I/113 showing Large osteoderms (asterisks), scale impressions (arrowhead) and dark, shiny ossicles (arrow). From Arbour et al. (2012).

The tail of ZPAL MgD I/113 (A) and Saichania (B), another common Ankylosaurid Dinosaur from Mongolia. (2) Sharp osteoderms with a triangular cross section. (8)Nearly flat, elongated oval-shaped osteoderms. Scale bar is 10 cm. From Arbour et al. (2012).