Yamaceratops Dorngobiensis, a New Primitive Ceratopsian (Dinosauria: Ornithischia) from the Cretaceous of Mongolia

Abstract

A new basal neoceratopsian taxon from the eastern Gobi Desert is described. Yamaceratops dorngobiensis, tax. nov., is probably of late Early Cretaceous age, and occupies a phylogenetic position intermediate between Liaoceratops and Archaeoceratops. It is the most basal taxon to display a number of traditional neoceratopsian synapomorphies concentrated in the cheek region and mandible. These include presence of an epijugal, lateral displacement of the coronoid process, a lateral ridge on the surangular for insertion of the jaw adductors, and a lateral wall to the mandibular glenoid. Yamaceratops shares two synapomorphies (tubercles on the ventral edge of the angular and shape of the jugal) with Liaoceratops, indicating that the transient presence of derived characters may be prevalent in the early evolutionary history of Ceratopsia. Yamaceratops shares aspects of frill morphology with Liaoceratops and Leptoceratops that suggest a function unrelated to display for this anatomical structure in basal neoceratopsians, and hints at a more complex evolutionary history for ceratopsian frills. Considerations of patristic distances and mosaic evolution among basal neoceratopsian taxa indicate that a greater diversity of these animals remains undiscovered.

Digital preparation of a probable neoceratopsian preserved within an egg, with comments on microstructural anatomy of ornithischian eggshells

“…Scale bar equals 5 mm do not reach as far laterally relative to the adult and the foramen magnum remains relatively large. The braincase is similar to other described juveniles (see Goodwin et al 2006) as well as that of fully mature P. andrewsi and Yamaceratops dorngobiensis in that the supraoccipital forms the dorsal margin of the foramen magnum (Brown and Schlaikjer 1940;Makovicky and Norell 2006;Fig. 3e and f).…”

“…The quadrate possesses a dorsal shaft that is elongate and compressed rostrocaudally, as seen in other basal neoceratopsians. The pterygoid flange extends medially from the ventral portion of the quadrate, but does not extend the length of the shaft as it does in the adult of Y. dorngobiensis (Makovicky and Norell 2006).…”

“…The sediments of this locality consist largely of a coarse sandstone that is interpreted as being fluvial in nature (see Makovicky and Norell 2006). The fauna at this locality is dominated by the neoceratopsian, Yamaceratops dorngobiensis, and also includes remains of primitive ornithopods, troodontids, dromaeosaursids, and several kinds of mammals and lizards.…”

Osteology of Gobiderma pulchrum (Monstersauria, Lepidosauria, Reptilia)

“…Indeed, the Cretaceous Gobi, particularly Djadokhta and similar deposits, is represented by a great number of species, including the three major dinosaurian clades (Ornithischia, Sauropodomorpha, and Theropoda; see, e.g., Makovicky and Norell, 2006;Norell, 2006, 2010;Turner et al, 2007aTurner et al, , 2007bMiles and Miles, 2009) as well as a diversity of mammals (see, e.g., Rougier et al, 2001;Wible et al, 2001;Wible et al, 2004), among other taxa (see Loope et al, 1998;Gao and Norell, 2000). Together, these fossils indicate the presence of thriving ecological communities with a broad taxonomic diversity despite xeric conditions.…”

A New Specimen of the Ornithischian DinosaurHaya griva, Cross-Gobi Geologic Correlation, and the Age of The Zos Canyon Beds

“…Over several field seasons these expeditions amassed a collection of over a thousand vertebrate specimens. These include the dinosaurs Yamaceratops dorngobiensis (Makovicky and Norell, 2006) and Haya griva (Makovicky et al, 2011), as well as a bird egg and embryo (Balanoff et al, 2008;Varricchio et al, 2015), several other dinosaurs, lizards, dinosaur eggs, and mammals. Eberth et al (2009) discussed the age and geology of this locality and determined that these beds lie conformably above the Cenomanian-Santonian Bayan Shire Formation.…”