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New neoceratopsian, Yamaceratops dorngobiensis
Makovicky, P.J. & M.A. Norell, 2006. Yamaceratops dorngobiensis, a new
primitive ceratopsian (Dinosauria: Ornithischia) from the Cretaceous of
Mongolia. American Museum Novitates 3530: 1-42.
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.