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Abstract
Most horned dinosaur remains recovered from the Aguja Formation in West Texas are referable to the endemic chasmosaurine Agujaceratops mariscalensis. One specimen, however, differs sufficiently to justify its designation as the holotype of a new species, Agujaceratops mavericus sp. nov. This specimen and an isolated postorbital horncore from the same vicinity are stratigraphically the highest found in the Aguja Formation. A well-preserved juvenile specimen exhibits some unique features, and others compatible with A. mavericus, but due to its immature condition cannot be identified with certainty. A parietal referred to A. mariscalensis is the most complete thus far known, and shows that the frill of this taxon is more elaborately ornamented than previously believed, bearing a set of large horn-like spikes at the posterolateral corners. These two species share features of the premaxilla and squamosal, which warrant their inclusion in the same genus. However, characters thought to distinguish the two species vary in a manner similar to that found in other chasmosaurines, where debate persists as to their taxonomic significance. A consensus species concept has yet to be adopted for ceratopsid genera, of which most are monotypic. As a result, the two Agujaceratops species could be interpreted as arbitrary anagenetic stages in a single lineage, end-members in a spectrum of ontogenetic and sex-associated variation in that lineage, or two sympatric lineages that occupied separate niches in the same range.
http://zoobank.org/urn:lsid:zoobank.org:pub:1846D524-AC7F-4126-8787-33B26D80CF52
Acknowledgements
The authors of the present study reflect the diversity of current opinion regarding ceratopsian taxonomy, spanning the gamut from taxonomic ‘lumper’ to ‘splitter’, and so we could not reach a complete consensus ourselves on interpretation of the Aguja ceratopsian material. The interpretation presented herein reflects a reasonable compromise, and we are resigned to await future discoveries in determining who may be ‘right’. In the meantime, we thank D. Corrick in the Division of Science & Resource Management at Big Bend National Park for his continued support of our work, J. Sagebiel and M. Brown at the Jackson School of Geosciences Vertebrate Paleontology Laboratory for access to specimens and curatorial assistance, and J. Browning of Texas Tech University for preparation of histologic sections. A. Farke and an anonymous reviewer provided helpful comments that substantially improved the content and presentation of the manuscript.