Info

Age

Geographic Location

Achelousaurus

Late Cretaceous

Western USA

Anchiceratops

Late Cretaceous

Alberta, Canada

Archaeoceratops

Early Cretaceous

China

Arrhinoceratops

Late

Cretaceous

Alberta, Canada

Avaceratops

Late

Cretaceous

Western USA

Bagaceratops

Late

Cretaceous

Mongolia

Brachyceratops

Late

Cretaceous

Western USA

Centrosaurus

Late

Cretaceous

Alberta, Canada

Chasmosaurus

Late

Cretaceous

Western USA; Alberta, Canada

Diceratops

Late

Cretaceous

Western USA

Einiosaurus

Late

Cretaceous

Western USA; Alberta, Canada

Leptoceratops

Late

Cretaceous

Western USA; Alberta, Canada

Liaoceratops

Late

Cretaceous

China

Monoclonius

Late

Cretaceous

Alberta, Canada; western USA

Montanoceratops

Late

Cretaceous

Western USA

Pachyrhinosaurus

Late

Cretaceous

Alberta, Canada; Alaska, USA

Pentaceratops

Late

Cretaceous

Western USA

Protoceratops

Late

Cretaceous

China, Mongolia

Psittacosaurus

Early Cretaceous

Mongolia, China, Thailand

Styracosaurus

Late Cretaceous

Western USA; Alberta, Canada

Torosaurus

Late Cretaceous

Western USA; Western Canada

Triceratops

Late Cretaceous

Western USA; Canada

Udanoceratops

Late Cretaceous

Mongolia

Zuniceratops

Late Cretaceous

Western USA

so far are from the Cretaceous, the Late Jurassic ceratopsian Chaoyangsaurus of China being the only exception. This time constraint distinguishes this important clade from theropods, sauropodomorphs, ornithopods, and thyreophorans (Chapters 9-12).

Members of Clade Marginocephalia are defined by several important character traits (Fig. 13.2).

■ A narrow shelf of bone on the parietal and posterior part of the squamosal, which projects from the skull posterior.

■ An abbreviated posterior portion of the premaxillary as it adds to the palate.

■ A shortened pubis accompanied by widely-spaced hip sockets.

Of these synapomorphies, the most important is the shelf of bone associated with the parietal and squamosal, an easily recognizable feature. Based on this trait and others, Marginocephalia unites the superficially disparate clades of Pachyceph-alosauria and Ceratopsia. Pachycephalosaurs are only represented by about 14 genera, thus their proposed cladistic classification consist of only a few options. In contrast, Ceratopsia is composed of a daunting number of genera and species within genera, and some genera closely resemble one another. Consequently, their cladistics present a major challenge for the few dinosaur paleontologists who work with ceraptosians.

Rostral

Rostral

Premaxillary abbreviated

Parietal and Squamosal shelf

Ilium

Premaxillary abbreviated

Ilium

Widely spaced hip sockets (Acetabula)

(Dorsal view)

FIGURE 13.2 Character traits of Marginocephalia: narrow shelf of bone on the parietal and posterior part of the squamosal; abbreviated posterior portion of premaxillary; and shortened pubis accompanied by widely spaced hip sockets.

Problems with ceratopsian taxonomy are attributable to two factors:

1 A very good body fossil record for ceratopsians, including numerous complete specimens for some species; and

2 overzealous naming of ceratopsian species in the past 100+ years, which resulted in many synonymies.

To illustrate how both facets have interacted, consider the following example. As many as 16 species names have been applied to the abundant remains of the genus Triceratops, despite a geologic range for the genus of less than 3 million years. Two explanations for this abundance of species are possible:

1 Evolutionary and genetic factors, such as interaction of environmental change, geographic isolation of small populations, genetic drift, and mutations, may have contributed to extremely rapid speciation for Triceratops (Chapter 6); and

2 Dinosaur paleontologists since the late nineteenth century may have used all newly-discovered features on a Triceratops skeleton to justify new species names.

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Responses

  • Natalie
    What is the geographic location of Udanoceratops?
    2 years ago

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