Nasutoceratopsini Ceratopsian From Campanian Cretaceous Alberta, Canada

A basal ceratopsid (Centrosaurinae: Nasutoceratopsini) from the Oldman Formation (Campanian) of Alberta, Canada

Authors:

Ryan et al

Abstract:

A partial skull (CMN 8804) of a ceratopsid from the upper unit of the Campanian Oldman Formation of Alberta is the first Canadian example of the newly established Nasutoceratopsini, a new subclade of Centrosaurinae defined as the stem-based clade of centrosaurine ceratopsids more closely related to Nasutoceratops titusi than to Centrosaurus apertus. The new clade is diagnosed, in part, by having a parietosquamosal frill lacking modified epimarginals; a small nasal horncore; large, rostrolaterally directed postorbital horncores; and a relatively short, deep face. Although the CMN 8804 taxon closely resembles Nasutoceratops, its phylogenetic position within Nasutoceratopsini is unresolved. The CMN 8804 taxon would have been contemporaneous with dinosaurs from the lower portion of the Dinosaur Park Formation 200 km to the northwest in Dinosaur Provincial Park. The presence of the CMN 8804 taxon in Alberta, and the approximately contemporaneous Nasutoceratops in Utah, indicates that the nasutoceratopsins persisted in both north and south Laramidia well after the first appearance (i.e., Coronosaurus brinkmani) of the newly defined Centrosaurini. This stem-based clade is composed of centrosaurine ceratopsids with well-adorned parietosquamosal frills and short postorbital horncores that are more closely related to Centrosaurus apertus than Pachyrhinosaurus canadensis. The rarity of nasutoceratopsins in the well-sampled sediments of Laramidia suggests that they may have had different ecological preferences than centrosaurins, or that their relatively non-diagnostic, fragmentary remains may be misidentified as other centrosaurins. The temporally (∼79–76 Ma) and geographically (Utah to Alberta) large distributions of Nasutoceratopsini weakens the hypothesis of distinct north and south Laramidian provinciality.

Machairoceratops cronusi: a new Ornate Centrosaurine Ceratopsid From Campanian Cretaceous Utah

A New Centrosaurine Ceratopsid, Machairoceratops cronusi gen et sp. nov., from the Upper Sand Member of the Wahweap Formation (Middle Campanian), Southern Utah

Authors:

Lund et al

Abstract:

The Upper Cretaceous (middle-late Campanian) Wahweap Formation of southern Utah contains the oldest diagnostic evidence of ceratopsids (to date, all centrosaurines) in North America, with a number of specimens recovered from throughout a unit that spans between 81 and 77 Ma. Only a single specimen has been formally named, Diabloceratops eatoni, from the lower middle member of the formation. Machairoceratops cronusi gen. et sp. nov., a new centrosaurine ceratopsid from the upper member of the Wahweap Formation, is here described based on cranial material representing a single individual recovered from a calcareous mudstone. The specimen consists of two curved and elongate orbital horncores, a left jugal, a nearly complete, slightly deformed braincase, the left squamosal, and a mostly complete parietal ornamented by posteriorly projected, anterodorsally curved, elongate spikes on either side of a midline embayment. The fan-shaped, stepped-squamosal is diagnostic of Centrosaurinae, however, this element differs from the rectangular squamosal in Diabloceratops. Machairoceratops also differs in the possession of two anterodorsally (rather than laterally) curved epiparietal ornamentations on either side of a midline embayment that are distinguished by a posteromedially-oriented sulcus along the entire length of the epiparietal. Additionally, the parietosquamosal frill is lacking any other epiossifications along its periphery. Machairoceratops shares a triangular (rather than round) frill and spike-like epiparietal loci (p1) ornamentation with the stratigraphically lower Diabloceratops. Both parsimony and Bayesian phylogenetic analyses place Machairoceratops as an early-branching centrosaurine. However, the parsimony-based analysis provides little resolution for the position of the new taxon, placing it in an unresolved polytomy with Diabloceratops. The resultant Bayesian topology yielded better resolution, aligning Machairoceratops as the definitive sister taxon to a clade formed by Diabloceratops and Albertaceratops. Considered together, both phylogenetic methods unequivocally place Machairoceratops as an early-branching centrosaurine, and given the biostratigraphic position of Machairoceratops, these details increase the known ceratopsid diversity from both the Wahweap Formation and the southern portion of Laramidia. Finally, the unique morphology of the parietal ornamentation highlights the evolutionary disparity of frill ornamentation near the base of Centrosaurinae.

A new Cenrosaurine Ceratopsian From Campanian Cretaceous Mexico

A Centrosaurine (Dinosauria: Ceratopsia) from the Aguja Formation (Late Campanian) of Northern Coahuila, Mexico

Authors:

Rivera-Silva et al

Abstract:

While centrosaurines and ceratopsids in general are abundant in the Late Campanian of northern Laramidia, they are much less commonly found in southern Laramidia. This has supported hypotheses of dinosaur provinciality and endemism in the Late Cretaceous with the delineation of at least two separate faunal zones, north and south Laramidia. There have been 12 genera of centrosaurines recognized from northern Laramidia while two genera, Diabloceratops and Nasutoceratops, have been named from southern Laramidia. We present an osteological description and taphonomic outline for a new centrosaurine ceratopsid from the Aguja Formation of northern Coahuila, Mexico that is not currently diagnosable to the generic level, but likely represents a new taxon. Further, we have included three-dimensional surface scans of all material attributed to this animal. Considering the large number of centrosaurines from northern Laramidia, it is likely that cladistic analyses are biased towards this faunal zone. New findings of southern centrosaurines are needed to correct this bias. This discovery expands the range of centrosaurines south to Coahuila, Mexico and adds new information to better characterize the morphology and taxonomy of centrosaurines from southern Laramidia and their evolution in comparison to their northern counterparts.