Regaliceratops

Credit: Julius Csotonyi.

*Regaliceratops* is an extinct genus of ceratopsian that lived in North America during the Late Cretaceous.

## History

Peter Hews discovered the holotype skull in 2005 from the St. Mary River Formation along the Oldman River from well cemented siltstone and with the tip of the rostrum sticking from the cliff. It was excavated in 2006 and 2008 by a team from the Royal Tyrrell Museum, described as complicated due to it being found near to a spawn point of the protected bull trout. It was nicknamed "Hellboy" for such difficult excavation, with the hard matric and small postorbital horncores and resorption pits adding to this. Caleb M. Brown and Donald M. Henderson (2015) named the specimen, TMP. 2005.055.0001, a nearly complete skull missing the rostrum, deformed by compression and having the rear and underside obscured by matrix. It is an adult based on fused sutures and rugose bone texture. *Regaliceratops* translates to "royal horned face": regalis, "royal" and ceratops, "horned face". The specific epithet, *peterhewsi*, is after geologist Peter Hews, who discovered the fossil.

## Description

Brown and Henderson (2015) diagnosed the genus as having a single epiparietal ossification at the midline is offset from the plane of the frill and other epiparietals towards the rostrum with parietals that project forwards and posteriorly and have a rough triangular transverse cross section, a midline ridge that is prominent at the parietal that merges with the median epiparietal, paired epiparietal ossifications that are long and flat with a roughly pentagonal shape, a prominent postorbital ridge that stretches diagonally from the supraorbital horncore to the squamosal base, parietal fenestrae that are smaller than in *Kosmoceratops*, and nasal horncores that are larger than the postorbital horncores of *Chasmosaurus belli* and *Vagaceratops*.

The snout is short and takk, though enhanced by tectonic shortening. The paire premaxillae form the median premaxillary septum, with the rostral portion being thin and making a prominent septal fossa, which lacks the accessory strut unlike *Triceratops* and *Titanoceratops*. The fossa is further thinning at the caudal and spreads through by the larger interpremaxillary fenestra, like *Anchiceratops*, *Triceratops* and *Titanoceratops*. It and other chasmosaurs have a caudal wall of the inferpremaxillary fenestra bounded by the condensed narial strut that moves from the floor to the upper process of the premaxilla. Unlike *Triceratops* and *Titanoceratops*, said strut is sinuous shaped. The premaxillae flare sideways into the rostroventral margin of the external nares on the rostral and ventral margins. The maxillary process projects to th caudodorsal from the flared premaxillary underside. Unlike taxa from the Campanian, the caudoventral process tapers caudally without forking, inserting between the maxilla and nasal with no constriction caudal to the horncore. Like *Chasmosaurus*, the midpoint of the horncore is positioned at the caudal extreme of the external naris. The nasal horncore has an estimated preserved height of 148 millimeters with a total range of 240-280 when the side slopes are extrapolated. This horncore is straight and has a tear drop shape in the horizontal cross section. The orbital margin has a sharp ridge that flares sideways and may be a result of post-depositional deformation, with a smooth confluent margin on the right-left margins. The orbits are very ellipsoid, unlike other ceratopsids who are only slightly. The rostrodorsal margin of the orbital rim consists of the palpebral, that swells to the sides and rostra, forming the antorbital buttress. This is larger than most chasmosaurs. Unlike *Kosmoceratops*, the postorbital horncore is slightly caudally arranged to the orbit and shares a narrow base. The postorbital horncores are upwards-stretching and procurved to wards the rostrum in the side, like *Pentaceratops*. These are smaller compared to the nasal and have vascular grooves over the surface.

The postorbital ridge is caudomedially present to the horncore, equivalent to the supraorbital squamosal scale row. The laterotemporal fenestrae are bounded by the jugal towards the rostrum and squamosal to the posterior. The orbital margin is smooth and thinned. The epijugal base is slightly smaller than the postorbital horncores. The caudal margin of the jugal borders the laterotemporal fenestrae, which is bordered by the laterotemporal process of the squamosal. However, this may not be true, since a distinct quadratojugal is not seen. The jugal notch bounds the squamosal to the posterior. The frill is nearly semicircular in the rostrodorsal with ossifications along the circumference; it is short, wide and has the greatest transverse width at the midlength like *Torosaurus* and *Triceratops*. The left squamosal has an elongate caudal with a lateral margin that has a prominent jugal notch and a following margin towards the rostrum that continues with the parietal caudal margin, further having triangular epiossifications. The lateral margin of the parietal has a straight suture with the medial edge of the squamosals and the caudal margin forminging the middle half of the frill. The caudalmost portion is at the midline, and the midline bars end in a rostrally-projecting bone. A prominent sagittal swelling is dominant on the midline of the parietal and keels. The large, medial epiparietal is positions where the sideways-curving epiparietal hooks in *Anchiceratops* and differing from the epiparietal hooks as it is with the confluent with the median ridge, being triangular in the cross section. A median epiossification at the parietal is possibly smaller than in *Ojoceratops* and *Bravoceratops*. The frill has 7 paired epiossifications that gradually decrease in size, similar in shape to *Anchiceratops* and similar in placement to *Triceratops*. 2 epiparietals are pentagonal in shape and may be the largest epiossifications in chasmosaurs. 3 triangular rostralmost episquamosals decrease in size towards the rostrum, with spade-shaped caudalmost episquamosals. The large pentagonal epiparietals and the smaller caudalmost episquamosals are transitional in size and shape. The cranial ornamentation is similar to centrosaurs, as the nasal horn and epiossifications are larger in relation to the postorbital horns and frill length. These similarities may indicate convergent evolution in horn morphology. Brown and Henderson (2015) suggest that they did so, but the extinction of centrosaurs in the Early Maastrichtian may correlate with this, as mammalian evolution often shows such links between behaviours and horn evolution.

## Paleoecology

*Regaliceratops* was discovered in the St. Mary River Formation of the Middle Maastrichtian of the Late Cretaceous. The lower stage was deposited in brackish water with the remaining formation deposited in freshwater fluvial floodplains. The formation is characterized by fine-grained sandstones, grey shales, coquinoid beds, carbonaeceous mudstones, coal beds, interbedded sandstone and siltstone, with some carbonaceous shale. Ginkgo, ferns, conifers, *Trapa*-like forms, *Sabal* and at leats 6 types of large monocot leaves are found. Additionally, *Edmontonia*, *Montanoceratops*, *Pachyrhinoceratops*, *Albertosaurus*, *Sauronitholestes*, *Troodon*, *Cimolomys*, *Meniscoessus*, *Mesodma*,*Cimolodon, Pediomys , Didelphodon*, *Eodelphis*, *Myledaphus*, *Lepisosteus*, *Leidyosuchus* and *Champsisaurus* are included in the fauna.

## References

https://en.wikipedia.org/wiki/Regaliceratops