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.2011 Jan 20;6(1):e16196.
doi: 10.1371/journal.pone.0016196.

Anatomy and taxonomic status of the chasmosaurine ceratopsid Nedoceratops hatcheri from the upper Cretaceous Lance Formation of Wyoming, U.S.A

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Anatomy and taxonomic status of the chasmosaurine ceratopsid Nedoceratops hatcheri from the upper Cretaceous Lance Formation of Wyoming, U.S.A

Andrew A Farke. PLoS One..

Abstract

Background: The validity of Nedoceratops hatcheri, a chasmosaurine ceratopsid dinosaur known from a single skull recovered in the Lance Formation of eastern Wyoming, U.S.A., has been debated for over a century. Some have argued that the taxon is an aberrant Triceratops, and most recently it was proposed that N. hatcheri represents an intermediate ontogenetic stage between "young adult" and "old adult" forms of a single taxon previously split into Triceratops and Torosaurus.

Methodology/principal findings: The holotype skull of Nedoceratops hatcheri was reexamined in order to map reconstructed areas and compare the specimen with other ceratopsids. Although squamosal fenestrae are almost certainly not of taxonomic significance, some other features are unique to N. hatcheri. These include a nasal lacking a recognizable horn, nearly vertical postorbital horncores, and relatively small parietal fenestrae. Thus, N. hatcheri is tentatively considered valid, and closely related to Triceratops spp. The holotype of N. hatcheri probably represents an "old adult," based upon bone surface texture and the shape of the horns and epiossifications on the frill. In this study, Torosaurus is maintained as a genus distinct from Triceratops and Nedoceratops. Synonymy of the three genera as ontogenetic stages of a single taxon would require cranial changes otherwise unknown in ceratopsids, including additions of ossifications to the frill and repeated alternation of bone surface texture between juvenile and adult morphotypes.

Conclusions/significance: Triceratops, Torosaurus, and likely Nedoceratops, are all distinct taxa, indicating that species richness for chasmosaurine ceratopsids in the Lance Formation just prior to the Cretaceous-Paleocene extinction was roughly equivalent to that earlier in the Cretaceous.

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Conflict of interest statement

Competing Interests:The author has read the journal's policy and has the following conflicts: 1) He is a section editor and academic editor for PLoS ONE.

Figures

Figure 1
Figure 1. Skull ofNedoceratops hatcheri, USNM 2412.
A. Photograph in right lateral view.B. Interpretive line drawing in right lateral view, with major reconstructed areas indicated in gray and matrix indicated in yellow.C. Photograph in left lateral view.D. Interpretive line drawing in left lateral view, with major reconstructed areas indicated in gray and matrix indicated in yellow. InC, the rostral end of the skull was broken away at the time of photography.Abbreviations:aof, antorbital fenestra;cc, caudal curve of oral margin;if, infratemporal fenestra;j, jugal;jn, jugal notch of squamosal;nh, nasal horncore;o, orbit;p, parietal;pf, parietal fenestra;poh, postorbital horncore;q, quadrate;rc, rostral curve of oral margin;sps, squamosal-parietal suture;sq, squamosal;sqf, squamosal fenestra. Scale bar equals 10 cm.
Figure 2
Figure 2. Skull ofNedoceratops hatcheri, USNM 2412.
A. Photograph in right oblique view.B. Photograph in rostral view.C. Interpretive line drawing in rostral view, with major reconstructed areas indicated in gray and matrix indicated in yellow.Abbreviations:aob, antorbital buttress;m, matrix and metal supports;nh, nasal horncore. Scale bar equals 10 cm, but note that parallax prevents accurate measurement of parts of the skull caudal to the external naris.
Figure 3
Figure 3. Skull ofNedoceratops hatcheri, USNM 2412.
A. Photograph in caudal view.B. Interpretive line drawing in caudal view, with major reconstructed areas indicated in gray and matrix and metal supports indicated in yellow.Abbreviations:ex, exoccipital;m, matrix;ms, metal support;q, quadrate;oc, occipital condyle;pf, parietal fenestra;pt, pterygoid;sf, squamosal fenestra;sps, squamosal-parietal suture. Scale bar equals 10 cm.
Figure 4
Figure 4. Close-up of rostral end of skull ofNedoceratops hatcheri, USNM 2412, in left lateral view.
Abbreviations: cpf, canal at edge of premaxillary fossa;en, endonaris;ftp, fossa on triangular process;m, matrix;mx, maxilla;nh, nasal horncore;ns, narial strut;pf, premaxillary fossa;r, rostral bone;tp, triangular process. Scale bar equals 10 cm.
Figure 5
Figure 5. Close-up of episquamosal on left squamosal ofNedoceratops hatcheri, USNM 2412.
Note the neurovascular impressions on the squamosal, suggestive of adult status. The caudal end is to the right of the image.Abbreviations: eps, episquamosal;nvi, neurovascular impressions. Scale bar equals 10 cm.
Figure 6
Figure 6. Close-up of right side of parietal and parietal fenestra ofNedoceratops hatcheri, USNM 2412.
The bone is shown in dorsal view, with the caudal end to the left of the image.Abbreviations:p, parietal;pf, parietal fenestra. Scale bar equals 10 cm.
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