Saturday, 5 July 2014

A highly specialized Musk Ox from the Late Miocene of Gansu Province, China.

In 1932 Birger Bohlin, chief palaeontologist with the explorer Sven Hedin’s Sino-Swedish Scientific Expedition to Northwest China, discovered an unusual Bovid skull from Miocene deposits in the Qaidam Basin, which he described under the name Tsaidamotherium hedini. The skull was partial, lacking the face and teeth, which are important for understanding the affinities and lifestyles of Bovids, but based upon the horn-core apparatus Bohlin assigned Tsaidamotherium hedini to the Ovibovini, or  Musk Oxen.

In a paper published in the journal Science China Earth Sciences on 29 October 2013, Shi QinQin of the Key Laboratory of Vertebrate Evolution and Human Origins at the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, described two new skulls, collected by local farmers in the Hezheng area of Gansu Province, which he assigns to a second species of Tsaidamotherium

The first skull is partial, comprising the cranial part of the skull, horn-core apparatus, basioccipital and occipital regions. This originated from the Liushu Formation at the Yancaiping fossil locality, roughly 2.5 km east of Maijiaji Township, and is now in the collection of Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences.

The second is an almost complete female skull with a damaged horn-core apparatus. This is known to be from the Hezheng area, though its exact provenance is unclear; it is now in the collection of the Hezheng Museum of Ancient Animal Fossils.

First skull of Tsaidamotherium brevirostrum; (a) posterior view, (b) ventral view. ab, auditory bulla; aas, accessory articular surface; Bo, basioccipital; Bs, Basisphenoid; cbl, compact bone layer; eam, external auditory meatus; et, ethmoid turbinates; fm, foramen magnum; for, foramen orbito-rotundum; fs, frontal sinus; fv, foramen ovale; hca, horn-core apparatus; iosof, interior opening of supraorbital foramen; obr, orbital rim; Oc, occipital; occ, occipital condyle; ocr, occipital crest; Pa, parietal; pal, parietal line; pf, posterior facet; pop, paroccipital process; pt, pharyngeal tuberosity; tf, temporal fossa. Scale bar is 2 cm. Shi (2013)

Tsaidamotherium brevirostrum, second skull, female individual; (a) dorsal view, (b) ventral view, (c) left lateral view, (d) anterior view, (e) posterior view. ef, ethmoid fissure; eosof, exterior opening of supraorbital foramen; exo, exostosis; fc, facial crista; Fr, frontal; ft, facial tuberosity; iof, infraorbital foramen; Ju, jugal; La, lachrymal; lo, lachrymal orifice; M1, first molar; M2, second molar; M3, third molar; Mx, maxilla; Na, nasal; nfs, nasal-frontal suture; P2, second premolar; P3, third premolar; P4, forth premolar; Pl, palatine; plf, palatine foramen; Pmx, premaxilla; Pt, pterygoid; ptp, pterygoid process; Tu, turbinates; za, zygomatic arch. Other abbreviations are the same as in preceding figures. Scale bar is 5 cm. Shi (2013).

The two skulls are deemed sufficiently similar to Tsaidamotherium hedini to be placed in the same genus, but distinct enough to be placed in a separate species, which Shi names Tsaidamotherium brevirostrum, meaning ‘short-muzzle’. The structure of the horn core apparatus of these skulls strongly supports Bohlin’s assertion that Tsaidamotherium is an Ovibovine (Musk Ox), though in many ways its cranial anatomy appears distinct and highly specialized, having a short snout and high nasal cavity. Comparison with modern Artiodactyls suggests this is likely to relate to life in a cold environment. It also has mesodont dentition, which suggests a browsing diet of leaves and twiggy material, similar to that of most modern Deer, rather than a grassy diet, which is most common in modern Bovids.

Skull reconstruction of Tsaidamotherium brevirostrum. (a) Reconstruction of skull and mandible, (b) profile reconstruction; the grey line shows the complementary bone structure. Shi (2013).

The Hezheng area lies in the southwest of the Linxia Basin, which in the Late Miocene is interpreted as having a hot semi-arid climate, based upon the fossil assemblages found across the basin. Shi suggests that by the Late Miocene the southwestern corner of the basin may have begun to undergo uplift associated with the Himalayan Orogeny (growth of the Himalayas), and that Tsaidamotherium brevirostrum may have dwelt in a old, mountain environment where it consumed a mixed diet of grasses, seeds, ferns, shrub vegetation and bamboo, similar to that consumed by the modern Takin (Himalayan Goat-antelope).

Sketch map of Hezheng area, Linxia Basin, showing fossil locality of Yancaiping. Shi (2013).

See also…


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