Regaliceratops

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Regaliceratops
Temporal range: Late Cretaceous, 68.5–67.5  Ma
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Regaliceratops skull at Royal Tyrrell Museum.jpg
Skull of Regaliceratops on display at the Royal Tyrrell Museum, Canada
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Ornithischia
Suborder: Ceratopsia
Family: Ceratopsidae
Subfamily: Chasmosaurinae
Tribe: Triceratopsini
Genus: Regaliceratops
Brown & Henderson, 2015
Type species
Regaliceratops peterhewsi
Brown & Henderson, 2015

Regaliceratops (meaning "Royal horned face") is a monospecific genus of chasmosaurine ceratopsid dinosaur from Alberta, Canada that lived during the Late Cretaceous (middle Maastrichtian stage, 68.5 to 67.5 Ma) in what is now the St. Mary River Formation. The type and only species, Regaliceratops peterhewsi, is known only from an adult individual with a nearly complete skull lacking the lower jaw, which was nicknamed "Hellboy". Regaliceratops was named in 2015 by Caleb M. Brown and Donald M. Henderson. Regaliceratops has an estimated length of 5 metres (16 ft) and body mass of 2 metric tons (2.2 short tons). The skull of Regaliceratops displays features more similar to centrosaurines, which suggests convergent evolution in display morphology in ceratopsids. [1]

Contents

Discovery and naming

St. Mary River Formation in Alberta, Canada St Mary River Fm Strata.jpg
St. Mary River Formation in Alberta, Canada

In 2005, a skull of a ceratopsid was discovered by geologist Peter Hews from the St. Mary River Formation, along the Oldman River in southwestern Alberta. The skull was located in well cemented siltstone and with the tip of the snout sticking out of a cliff. The skull was excavated in 2006 and 2008 by a team of the Royal Tyrrell Museum and was removed in blocks. The excavation was described as being complicated as the specimen was in close proximity to protected spawning habitat of bull trout in the river. The specimen was nicknamed "Hellboy" due to difficultly and time consuming excavation, in addition to the hard matrix, and the presence of small postorbital horncores with resorption pits. The specimen was subsequently named and described in 2015 by Caleb M. Brown and Donald M. Henderson. [1]

The holotype specimen, TMP 2005.055.0001, consists of a nearly complete skull that is missing only the rostrum. The skull was deformed by compression and its rear and underside are obscured by the matrix. The specimen represents an adult individual as the cranial elements are fused together and the bone surface texture is rugose, unlike that of juvenile and subadult ceratopsids. [1]

The generic name, Regaliceratops, is derived from the Latin word "regalis" (royal) and the Greek words "keras", (horn), and "ops", (face). The generic name is in reference to the crown-shaped parietosquamosal frill and the Royal Tyrrell Museum. The specific name, peterhewsi, honours the geologist Peter Hews, who discovered the type specimen. [1]

Description

Size and distinguishing traits

Restoration with Hypacrosaurus and Leptoceratops Regaliceratops peterhewsi abelov.jpg
Restoration with Hypacrosaurus and Leptoceratops

Regaliceratops was a large ceratopsian, reaching 5 metres (16 ft) in length and 2 metric tons (2.2 short tons) in body mass. [2]

Brown & Henderson (2015) diagnosed Regaliceratops based on the presence of a single, midline epiparietal ossification that is offset from the plane of the frill and other epiparietals towards the rostrum with parietals projecting towards the posterior end that have a roughly triangular transverse cross-section; a prominent midline ridge on that parietal that merges with the median epiparietal; paired epiparietal ossifications that are long, flat, and roughly pentagonal shaped; a prominent postorbital ridge that runs diagonally from the supraorbital horncore to the base of the squamosal; parietal fenestrae that are small in size to orbit as in Kosmoceratops ; and nasal horncores that are larger than the postorbital horncores as in Chasmosaurus bellis and Vagaceratops . [1]

Cranium

Holotype skull from the front. Regaliceratops - Royal Tyrrell Museum.jpg
Holotype skull from the front.

The snout of the holotype specimen is short and tall, although it has been exaggerated by the tectonic shortening of the skull. The paired premaxillae form the median premaxillary septum, with the rostral portion of the median premaxillary septum being thin forming the prominent septal fossa. Unlike Triceratops and Titanoceratops , the prominent septal fossa lacks the accessory strut. The fossa is further thinned at the caudal portion and is spread throughout by the presence of a large interpremaxillary fenestra as in Anchiceratops , Arrhinoceratops and Triceratops . Regaliceratops, and other chasmosaurines, has the caudal wall of the interpremaxillary fenestra bounded by a condensed narial strut that moves back and forth from the floor of the premaxillae to the upper process of the premaxillae. Unlike Titanoceratops and Triceratops, the narial strut isn't as broad and triangular but is, instead, sinuous in shape. The premaxillae flare towards the sides which form the rostroventral margin of the external nares on the rostral and ventral margins. The maxillary process projects caudodorsally from the flared underside aspect of the premaxilla. Unlike Campanian chasmosaurines such as Chasmosaurus and Utahceratops , the caudoventral process of Regaliceratops tapers caudally without forking, and inserts between the maxilla and nasal towards the sides. The upper margin of the external naris is formed by the rostral process and horncore base, and extends caudal to the rostral margin of the maxillary tooth row. As in Bravoceratops , the nasal shows no constriction situated caudal to the horncore. As in 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 mm and an estimated total height range of 240 to 280mm when the side slopes of the horncore are extrapolated. The nasal horncore is straight and has a tear drop shape in horizontal cross section. [1]

Holotype skull from the side. Regaliceratops Royal Tyrrell 1.jpg
Holotype skull from the side.

The orbital margin shows a sharp ridge that flares towards the sides, which may be a result of post-depositional deformation, and a smooth confluent margin on the right and left margins. The orbits are highly ellipsoidal, unlike other ceratopsids that have slightly ellipsoidal orbits. The rostrodorsal margin of the orbital rim consists of the palpebral, and swells towards the sides and rostrums which forms an antorbital buttress. The antorbital buttress is larger than that of most chasmosaurines. Unlike Kosmoceratops, the postorbital horncore of Regaliceratops is arranged slightly caudal to the orbit but shares the narrow base. The postorbital horncores are also directed upwards and are procurved towards the rostrum in side view, as in Pentaceratops . The postorbital horncores are smaller in size to the nasal horncore and has a surface that is oriented vascular grooves. A prominent postorbital ridge is present caudomedially to the horncore which is equivalent to the supraorbital squamosal scale row. The laterotemporal fenestrae are bounded by the jugal towards the rostrum and squamosal towards the posterior. The orbital margin is smooth and not thickened. The base of the epijugal is only slightly smaller than the postorbital horncores. The jugal's caudal margin forms the border of the laterotemporal fenestrae, which is also bordered by the laterotemporal process of the squamosal. However, this may not have been the true morphology due to the lack of a distinct quadratojugal. Bounded by the squamosal towards the posterior is the jugal notch. [1]

Skull of Triceratops, a close relative of Regaliceratops Triceratops skull FMNH.jpg
Skull of Triceratops, a close relative of Regaliceratops

The frill of Regaliceratops is nearly semicircle in shape in rostrodorsal view, with ossifications along the circumference. The frill is also short and wide, with the greatest transverse width being located at its midlength as in Torosaurus and Triceratops. The left squamosal has an elongated caudal portion, with a lateral margin that has a prominent jugal notch that is followed by a margin towards the rostrum that is continuous with that of the parietal caudal margin and bears triangular epiossifications. The lateral margin of the parietal has a straight suture with the medial edge of the squamosals and the caudal margin forms the middle half of the broad semicircle of the frill. The frill's caudalmost portion is located in the midline and the midline bars ends in a rostrally projecting bone. A prominent sagittal swelling is dominant on the midline of the parietal and forms a keel. The large, medial epiparietal is positioned where the sideways curving epiparietal hooks of Anchiceratops are and differs from the epiparietal hooks as it is confluent with the median ridge and is triangular in cross-section. A median epiossification on the parietal of the frill is possibly similar to those of Ojoceratops and Bravoceratops. The frill is also adorned with seven paired epiossifications that gradually decrease in size, which are similar in shape to those of Anchiceratops but are similar in placement to Triceratops. Two epiparietals are pentagonal in shape and may represent the largest epiossifications recorded in chasmosaurines. Triangular in shape are three rostralmost episquamosals which decrease in size towards the rostrum, while spade-shaped is the caudalmost episquamosal. The large pentagonal epiparietals and the smaller caudalmost episquamosal are both transitional in size and shape. The cranial ornamentation of Regaliceratops is similar to that of centrosaurine ceratopsids as the nasal horn and epiossifications are represented as larger relative to the postorbital horns and frill length. The similarities between the cranial ornamentation of Regaliceratops and centrosaurines indicates convergent evolution in horn morphology. Brown & Henderson (2015) hypothesised that, not only did it convergently evolve morphologically, but also behaviourally after the extinction of centrosaurines in the early Maastrichtian as convergent horn evolution in mammals often correlates with convergent social behaviours. [1]

Classification

Brown & Henderson (2015) originally placed Regaliceratops within Triceratopsini, in a polytomy with Eotriceratops , Ojoceratops , and a clade containing more nested taxa such as Nedoceratops , Titanoceratops , Triceratops and Torosaurus . [1] However, Mallon et al. (2016) found Regaliceratops to be outside of Triceratopsini, in a polytomy with Anchiceratops , Arrhinoceratops and Triceratopsini. [3] Dalman et al. (2022) once more recovered Regaliceratops within Triceratopsini, sister taxon to Triceratops horridus , Triceratops prorsus and Ojoceratops. [4]

A phylogenetic analysis conducted by Mallon et al. (2016) is reproduced below. [3]

Anchiceratops ornatus

Regaliceratops peterhewsi

Arrhinoceratops brachyops

Triceratopsini

Ojoceratops fowleri

Titanoceratops ouranos

Nedoceratops hatcheri

Torosaurus latus

"Torosaurus" utahensis

Triceratops prorsus

Triceratops horridus

The results of an earlier analysis by Brown & Henderson (2015) are reproduced below. [1]

Triceratopsini

Regaliceratops peterhewsi

Eotriceratops xerinsularis

Ojoceratops fowleri

Titanoceratops ouranos

Nedoceratops hatcheri

Torosaurus latus

Torosaurus utahensis

Triceratops horridus

Triceratops prorsus

Paleoenvironment

Pachyrhinosaurus, a centrosaurine ceratopsid contemporaneous with Regaliceratops. Pachyrhinosaurus perotorum skeleton.jpg
Pachyrhinosaurus, a centrosaurine ceratopsid contemporaneous with Regaliceratops.

Regaliceratops is known from the St. Mary River Formation which has been dated to the middle Maastrichtian stage of the Late Cretaceous period. [1] The lower St. Mary River Formation was deposited in brackish water environments, with the remainder of the formation being deposited in freshwater fluvial and floodplain environments. The formation is characterized by fine-grained sandstones, grey shales, coquinoid beds, carbonaceous mudstones, coal beds, interbedded sandstone and siltstone, with minor occurrences of carbonaceous shale. Ferns, ginkgoes, conifers, Trapa-like plants, sabaloid palms and at least six types of large monocot leaves are known from the formation. [5] [6] [7]

The fauna of the St. Mary River Formation consists of the nodosaurid ankylosaur Edmontonia , the leptoceratopsid ceratopsian Montanoceratops , the centrosaurine ceratopsid Pachyrhinosaurus , a ceratopsid that was previously considered to be Anchiceratops, the albertosaurine tyrannosaurid Albertosaurus , the saurornitholestine dromaeosaurid Saurornitholestes , the troodontid Troodon , [8] the mammals Cimolomys , Meniscoessus , Mesodma , Cimolodon , Pediomys, Didelphodon and Eodelphis , the fish Myledaphus and Lepisosteus , the crocodylomorph Leidyosuchus , and the choristodere Champsosaurus . [9]

See also

Related Research Articles

<i>Torosaurus</i> Extinct genus of dinosaurs

Torosaurus is a genus of herbivorous chasmosaurine ceratopsian dinosaur that lived during the late Maastrichtian age of the Late Cretaceous period, between 68 and 66 million years ago, though it is possible that the species range might extend to as far back as 69 million years ago. Fossils have been discovered across the Western Interior of North America, from as far north as Saskatchewan to as far south as Texas.

<i>Einiosaurus</i> Ceratopsian dinosaur genus from Upper Cretaceous period

Einiosaurus is a genus of herbivorous centrosaurine ceratopsian dinosaur from the Upper Cretaceous of northwestern Montana. The name means 'bison lizard', in a combination of Blackfeet Indian eini and Latinized Ancient Greek sauros; the specific name (procurvicornis) means 'with a forward-curving horn' in Latin. Einiosaurus is medium-sized with an estimated body length at 4.5 metres (15 ft).

<i>Achelousaurus</i> Genus of ceratopsid dinosaur from North America

Achelousaurus is a genus of centrosaurine ceratopsid dinosaur that lived during the Late Cretaceous Period of what is now North America, about 74.2 million years ago. The first fossils of Achelousaurus were collected in Montana in 1987, by a team led by Jack Horner, with more finds made in 1989. In 1994, Achelousaurus horneri was described and named by Scott D. Sampson; the generic name means "Achelous lizard", in reference to the Greek deity Achelous, and the specific name refers to Horner. The genus is known from a few specimens consisting mainly of skull material from individuals, ranging from juveniles to adults.

<i>Anchiceratops</i> Extinct genus of dinosaurs

Anchiceratops is an extinct genus of chasmosaurine ceratopsid dinosaur that lived approximately 72 to 71 million years ago during the latter part of the Cretaceous Period in what is now Alberta, Canada. Anchiceratops was a medium-sized, heavily built, ground-dwelling, quadrupedal herbivore that could grow up to an estimated 4.3 metres (14 ft) long. Its skull featured two long brow horns and a short horn on the nose. The skull frill was elongated and rectangular, its edges adorned by coarse triangular projections. About a dozen skulls of the genus have been found.

<i>Medusaceratops</i> Extinct genus of dinosaurs

Medusaceratops is an extinct genus of centrosaurine ceratopsian dinosaur known from the Late Cretaceous Judith River Formation of Montana, northern United States. It contains a single species, Medusaceratops lokii.

<span class="mw-page-title-main">Chasmosaurinae</span> Extinct subfamily of dinosaurs

Chasmosaurinae is a subfamily of ceratopsid dinosaurs. They were one of the most successful groups of herbivores of their time. Chasmosaurines appeared in the early Campanian, and became extinct, along with all other non-avian dinosaurs, during the Cretaceous–Paleogene extinction event. Broadly, the most distinguishing features of chasmosaurines are prominent brow horns and long frills lacking long spines; centrosaurines generally had short brow horns and relatively shorter frills, and often had long spines projecting from their frills.

<i>Kosmoceratops</i> Dinosaur genus from the Late Cretaceous period

Kosmoceratops is a genus of ceratopsid dinosaur that lived in North America about 76–75.9 million years ago during the Late Cretaceous period. Specimens were discovered in Utah in the Kaiparowits Formation of the Grand Staircase–Escalante National Monument in 2006 and 2007, including an adult skull and postcranial skeleton and partial subadults. In 2010, the adult was made the holotype of the new genus and species Kosmoceratops richardsoni; the generic name means "ornate horned face", and the specific name honors Scott Richardson, who found the specimens. The find was part of a spate of ceratopsian discoveries in the early 21st century, and Kosmoceratops was considered significant due to its elaborate skull ornamentation.

<i>Vagaceratops</i> Extinct genus of reptiles

Vagaceratops is a genus of herbivorous ceratopsian dinosaur. It is a chasmosaurine ceratopsian which lived during the Late Cretaceous period in what is now Alberta. Its fossils have been recovered from the Upper Dinosaur Park Formation. It is sometimes included in the genus Chasmosaurus as Chasmosaurus irvinensis instead of being recognized as its own genus.

<span class="mw-page-title-main">Triceratopsini</span> Extinct tribe of dinosaurs

Triceratopsini is a tribe of herbivorous chasmosaurine dinosaurs that lived between the late Campanian to the late Maastrichtian stages of the Cretaceous period, between 74.73 and 66 million years ago. Fossils of these animals have been found in western North America, in particular West Canada, Western and Midwestern United States, which was once part of the ancient continent of Laramidia. The tribe was named by Nicholas R. Longrich in 2011 for the description of Titanoceratops, which he defined as "all species closer to Triceratops horridus than to Anchiceratops ornatus or Arrhinoceratops brachyops". Triceratopsins were the largest of the chasmosaurines; suggesting that gigantism had evolved in the Ceratopsidae once. In addition there is an evolutionary trend in the solidification of the frills, the most extreme being in Triceratops.

<i>Nasutoceratops</i> Extinct genus of dinosaurs

Nasutoceratops is an extinct genus of ceratopsian dinosaur. It is a basal centrosaurine which lived during the Late Cretaceous Period. Fossils have been found in southern Utah, United States. Nasutoceratops was a large, ground-dwelling, quadrupedal herbivore with a short snout and unique rounded horns above its eyes that have been likened to those of modern cattle. Extending almost to the tip of its snout, these horns are the longest of all the members of the centrosaurine subfamily. The presence of pneumatic elements in the nasal bones of Nasutoceratops are a unique trait and are unknown in any other ceratopsid.

<i>Xenoceratops</i> Extinct genus of dinosaurs

Xenoceratops is a genus of centrosaurine ceratopsid dinosaur known from the Late Cretaceous, and is known to have lived in what is currently Alberta, Canada. The genus has one known species, Xenoceratops foremostensis. Its remains were discovered in the Foremost Formation.

<i>Coronosaurus</i> Extinct genus of dinosaurs

Coronosaurus is a genus of centrosaurine ceratopsian dinosaurs which lived in the Late Cretaceous, in the middle Campanian stage. Its remains, two bone beds, were discovered by Phillip J. Currie in the Oldman Formation of Alberta, Canada, and its type and only species, Coronosaurus brinkmani, was first described in 2005, as a new species within the genus Centrosaurus. Later studies questioned the presence of a direct relationship, and in 2012 it was named as a separate genus. Coronosaurus means "crowned lizard", coming from "corona", Latin for crown, and "sauros", Greek for lizard; this name refers to the unique, crown-like shape of the horns on the top of its frill.

<i>Judiceratops</i> Extinct genus of dinosaurs

Judiceratops is an extinct horned dinosaur. It lived around 78 million years ago, during the Late Cretaceous Period in what is now Montana, United States. Like other horned dinosaurs, Judiceratops was a large, quadrupedal herbivore. It is the oldest known chasmosaurine.

Bravoceratops is a genus of large chasmosaurine ceratopsid dinosaur that lived approximately 70 million years ago, and is known from the Late Cretaceous Javelina Formation in what is now Texas, United States.

<i>Mercuriceratops</i> Extinct genus of dinosaurs

Mercuriceratops is an extinct genus of herbivorous chasmosaurine ceratopsid dinosaur known from the Late Cretaceous of Alberta, Canada and Montana, United States. It contains a single species, Mercuriceratops gemini.

<i>Wendiceratops</i> Extinct genus of dinosaurs

Wendiceratops is a genus of herbivorous centrosaurine ceratopsian dinosaur from the Late Cretaceous of Canada.

<i>Spiclypeus</i> Extinct genus of dinosaurs

Spiclypeus is an extinct genus of chasmosaurine ceratopsian dinosaur known from the Late Cretaceous Judith River Formation of Montana, United States.

<i>Yehuecauhceratops</i> Extinct genus of dinosaurs

Yehuecauhceratops is a genus of horned centrosaurine ceratopsid dinosaur from the Late Cretaceous of Coahuila, Mexico. It contains a single species, Y. mudei, described from two partial specimens by Rivera-Sylva et al. in 2016 and formally named by Rivera-Sylva et al. in 2017. It was a small centrosaurine with a body length of 3 metres (9.8 ft), making it smaller than Agujaceratops and Coahuilaceratops, the other two ceratopsids in its environment; the three may have been ecologically segregated. A ridge bearing a single roughened projection near the bottom of the squamosal bone, which probably supported a small horn, allows Yehuecauhceratops to be distinguished from other centrosaurines. Its affinities to nasutoceratopsin centrosaurines, such as Avaceratops and Nasutoceratops, are supported by various morphological similarities to the former.

<i>Terminocavus</i> Genus of ceratopsid dinosaurs (fossil)

Terminocavus is a genus of ceratopsid dinosaur from the late Cretaceous Period of what is now North America. The genus contains a single species, the type species Terminocavus sealeyi, known from a parietal and some other associated fragments. The holotype specimen was discovered in the Kirtland Formation of New Mexico in 1997, and was later described and named in a 2020 study. It was similar in anatomy to Pentaceratops and Anchiceratops, which it was closely related to, but had a distinctive heart-shaped upper frill with very narrow notch. It has been hypothesized to form an anagenetic series with several other chasmosaur species.

<i>Bisticeratops</i> Extinct genus of chasmosaurine dinosaurs

Bisticeratops is a genus of chasmosaurine ceratopsian from outcrops of the Campanian age Kirtland Formation found in the Bisti/De-Na-Zin Wilderness in northwestern New Mexico, United States. The type and only species is B. froeseorum, known from a nearly complete skull.

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