Abstract
BackgroundThe holotype and only specimen of the chasmosaurine ceratopsid dinosaur ‘Nedoceratops hatcheri’ has been the source of considerable taxonomic debate since its initial description. At times it has been referred to its own genus while at others it has been considered synonymous with the contemporaneous chasmosaurine Triceratops. Most recently, the debate has focused on whether the specimen represents an intermediate ontogenetic stage between typical young adult Triceratops and the proposed mature morphology, which was previously considered to represent a distinct genus, ‘Torosaurus’.Methodology/Principal FindingsThe only specimen of ‘Nedoceratops hatcheri’ was examined and the proposed diagnostic features of this taxon were compared with other chasmosaurine ceratopsids. Every suggested autapomorphy of ‘Nedoceratops’ is found in specimens of Triceratops. In this study, Triceratops includes the adult ‘Torosaurus’ morphology. The small parietal fenestra and elongate squamosals of Nedoceratops are consistent with a transition from a short, solid parietal-squamosal frill to an expanded, fenestrated condition. Objections to this hypothesis regarding the number of epiossifications of the frill and alternations of bone surface texture were explored through a combination of comparative osteology and osteohistology. The synonymy of the three taxa was further supported by these investigations.Conclusions/SignificanceThe Triceratops, ‘Torosaurus’, and ‘Nedoceratops’ morphologies represent ontogenetic variation within a single genus of chasmosaurine: Triceratops. This study highlights how interpretations of dinosaur paleobiology, biodiversity, and systematics may be affected by ascribing ontogenetic and other intraspecific variation a taxonomic significance.
Highlights
For many years after the description of the first species of Triceratops (T. horridus) [1], nearly every variation in cranial morphology between specimens was considered sufficient grounds to erect new species
Nedoceratops hatcheri is distinguished from Triceratops spp. in the position of the ventral extremity of the squamosal well above the alveolar process of the maxilla, and in the presence of parietal fenestrae, which are lacking in Triceratops species
Nedoceratops hatcheri is distinguished from Torosaurus latus in squamosal shape, and that N. hatcheri has extremely reduced parietal fenestrae and a low number of episquamosals relative to T. latus.’’
Summary
For many years after the description of the first species of Triceratops (T. horridus) [1], nearly every variation in cranial morphology between specimens was considered sufficient grounds to erect new species. By 1949, as many as 16 species of this genus had been named [2,3,4] After his initial description of Triceratops, O.C. Marsh named two species of a new genus of latest Cretaceous ceratopsid (‘Torosaurus’), which were found in the same geological formation and geographic area as the Triceratops specimens [5]. The holotype and only specimen of the chasmosaurine ceratopsid dinosaur ‘Nedoceratops hatcheri’ has been the source of considerable taxonomic debate since its initial description. The debate has focused on whether the specimen represents an intermediate ontogenetic stage between typical young adult Triceratops and the proposed mature morphology, which was previously considered to represent a distinct genus, ‘Torosaurus’
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
