Yamaceratops dorngobiensis

MAKOVICKY, PETER J & NORELL, MARK A, 2006, Yamaceratops dorngobiensis, a New Primitive Ceratopsian (Dinosauria: Ornithischia) from the Cretaceous of Mongolia, American Museum Novitates 3530 (1), pp. 1-44 : 2-3

Yamaceratops dorngobiensis , new taxon

ETYMOLOGY: The genus is named for Yama, a Tibetan tantric Buddhist deity, who is the Lord of Death and one of the eight Dharmapalas, or protectors, of Buddhist teaching. Yama has the head of a water buffalo and bears horns, a trait from which ceratopsians derive their name. The specific name refers to the Eastern Gobi provenance of this taxon.

LOCALITY AND GEOLOGICAL SETTING: The specimen derives from a fluvial, pale red sandstone layer at Khugenetslavkant. These redbeds appear to overlie the Khar Khutul (5 Khar Hötöl) beds and underlie an unnamed unit with a fauna of segnosaurs, advanced iguanodontians, and ornithomimosaurs reminiscent of the Iren Dabasu fauna ( Gilmore, 1933; Currie and Eberth, 1993). The Khar Khutul beds may be correlated with the Khuren Dukh (5 Hüren Dukh) beds that have been interpreted as Aptian–early Albian in age ( Jerzykiewicz and Russell, 1991; Khand et al., 2000), but have also been dated as Barremian (,128 MYA) by Shuvalov (2000). The age of the Iren Dabasu fauna has been poorly constrained with ages ranging from the Cenomanian to the early Campanian ( Jerzykiewicz and Russell, 1991; Currie and Eberth, 1993; Khand et al., 2000). If the correlations outlined above are correct, the Khugenetslavkant sandstone facies appears to be late Early Cetaceous in age. This is roughly similar or perhaps slightly younger than the Albian age ascribed to Archaeoceratops (Tang et al., 2001) . Stratigraphic relationships among central Asian continental sediments are still poorly understood and much work remains to be done in this respect.

DIFFERENTIAL DIAGNOSIS: Small basal ceratopsian taxon with unkeeled rostral unlike all other Neoceratopsia (optimization-dependent unique trait); rostral patterned with anastomosing ridges and grooves (present in neoceratopsians more derived than Liaoceratops ); subtemporal part of jugal lobate and deeper than suborbital section (plesiomorphic for Neoceratopsia , shared only with Liaoceratops ); epijugal ossification present (plesiomorphic for neoceratopsians other than Liaoceratops ); angular with two tubercles along ventral edge (unique trait; three tubercles present in Liaoceratops ); surangular forming vertical wall to glenoid (plesiomorphic for neoceratopsians more derived than Liaoceratops ); all cheek teeth with distinct, offset primary ridge (plesiomorphic for neoceratopsians more derived than Liaoceratops ).

HOLOTYPE: The holotype ( IGM 100 /1315) consists of a partial skull missing the premaxillae, rostral, and predentary, as well as much of the frill and the left cheek and posterior part of the left mandible. The holotype skull appears to be from a mature individual, as witnessed by closure of the sutures among the occipital and basicranial braincase elements. The epijugal is not fused to the jugal, a feature that appears to be related to advanced maturity in Protoceratops andrewsi and ceratopsids. The skull is only dorsoventrally compacted to a small degree.

REFERRED MATERIALS: A referred specimen ( IGM 100/1303) collected in 2002 comprises the rostral, left maxilla, right jugal and quadrate, the left surangular, both articulars, a few isolated teeth, three partial vertebrae, the left ilium, and several hindlimb fragments. Additionally, a large number of fragmentary ceratopsian bones were surface collected from the Khugenetslavkant locality by the 2002 and 2003 AMNH-MAS field crews. An isolated predentary, IGM 100/1867, is described here and can safely be referred to Yamaceratops based on its similarity with the predentaries of other basal neoceratopsians.