Mercuriceratops
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''Mercuriceratops'' is an
extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of herbivorous
chasmosaurine 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, durin ...
ceratopsid Ceratopsidae (sometimes spelled Ceratopidae) is a family of ceratopsian dinosaurs including ''Triceratops'', ''Centrosaurus'', and ''Styracosaurus''. All known species were quadrupedal herbivores from the Upper Cretaceous. All but one species are k ...
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
known from the
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
(
Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campanian s ...
stage) of
Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...
, Canada and
Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columbi ...
, United States. It contains a single species, ''Mercuriceratops gemini''.


Discovery

In 2007, Triebold Paleontology Inc found frill elements in
Fergus County, Montana Fergus County is a county in the U.S. state of Montana. As of the 2020 census, the population was 11,446. Its county seat is Lewistown. The county was founded in 1885 and named for James Fergus, a Montana politician who was instrumental in cr ...
. In 2014, the
type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...
''Mercuriceratops gemini'' was named and described by Michael Ryan, David Evans,
Philip John Currie Philip John Currie (born March 13, 1949) is a Canadian palaeontologist and museum curator who helped found the Royal Tyrrell Museum of Palaeontology in Drumheller, Alberta and is now a professor at the University of Alberta in Edmonton. In the ...
and Mark Loewen. The generic name combines the name of the Roman god
Mercury Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...
, a reference to the similarity of the neck shield to the winged helmet of the messenger of the gods, with ~ceratops, "horn face", a usual suffix in ceratopian names. The specific name is that of the constellation
Gemini Gemini may refer to: Space * Gemini (constellation), one of the constellations of the zodiac ** Gemini in Chinese astronomy * Project Gemini, the second U.S. crewed spaceflight program * Gemini Observatory, consisting of telescopes in the Northern ...
, named after the twins
Castor and Pollux Castor; grc, Κάστωρ, Kástōr, beaver. and Pollux. (or Polydeukes). are twin half-brothers in Greek and Roman mythology, known together as the Dioscuri.; grc, Διόσκουροι, Dióskouroi, sons of Zeus, links=no, from ''Dîos'' ('Z ...
, in reference to the similar specimens the species is based on. The species is represented only by two
squamosal bone The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral co ...
s collected from approximately time-equivalent sections of the upper
Judith River Formation The Judith River Formation is a fossil-bearing geologic formation in Montana, and is part of the Judith River Group. It dates to the Late Cretaceous, between 79 and 75.3 million years ago, corresponding to the "Judithian" land vertebrate age. It ...
and the lower
Dinosaur Park Formation The Dinosaur Park Formation is the uppermost member of the Belly River Group (also known as the Judith River Group), a major geologic unit in southern Alberta. It was deposited during the Campanian stage of the Late Cretaceous, between about 76. ...
. The
holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...
, ROM 64222, was found by Triebold, in layer of the Judith River Formation dating from the middle Campanian, about seventy-seven million years old. It consists of a partial right squamosal, possibly of a subadult individual. It was acquired by the
Royal Ontario Museum The Royal Ontario Museum (ROM) is a museum of art, world culture and natural history in Toronto, Ontario, Canada. It is one of the largest museums in North America and the largest in Canada. It attracts more than one million visitors every year ...
. The second specimen, UALVP 54559, was referred. It too is a partial right squamosal but slightly larger and probably of an older individual. It was found by Susan Owen-Kagen, a preparator at the
University of Alberta The University of Alberta, also known as U of A or UAlberta, is a public research university located in Edmonton, Alberta, Canada. It was founded in 1908 by Alexander Cameron Rutherford,"A Gentleman of Strathcona – Alexander Cameron Rutherfor ...
, at a distance of 380 kilometres from the holotype, in Alberta in the Dinosaur Provincial Park, on the north bank of the Red Deer River, one kilometre east of Happy Jack's Cabin, in a layer of the lower Dinosaur Park Formation, two metres above the
Oldman Formation The Oldman Formation is a stratigraphic unit of Late Cretaceous (Campanian stage) age that underlies much of southern Alberta, Canada. It consists primarily of sandstones that were deposited in fluvial channel and floodplain environments. It was ...
. Associated with UALVP 54559, remains of a brow horn core were discovered but these were not referred because the connection with the squamosal was considered too uncertain.


Description

''Mercuriceratops'' was a medium-sized ceratopsian, reaching in length and in body mass. The holotype squamosal has a length of . Ryan ''et al.'' (2014) established a single
autapomorphy In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to t ...
, unique derived trait, of ''Mercuriceratops''. The squamosal possesses a rear branch that is narrowed and rod-shaped instead of being blunt, triangular and tapering, the normal chasmosaurine form, or broadly rounded as with ''
Triceratops ''Triceratops'' ( ; ) is a genus of herbivore, herbivorous Chasmosaurinae, chasmosaurine Ceratopsidae, ceratopsid dinosaur that first appeared during the late Maastrichtian stage of the Late Cretaceous Period (geology), period, about 68 m ...
''. The narrowing is caused by an indentation of the outer rim of the squamosal. The squamosal carries at least six, and perhaps as many as eight, episquamosals,
osteoderms Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct ...
on the frill rim. Based on the narrow form of the squamosal, it was deduced that the inner shield bones, the parietals, were very wide and pierced by enormous parietal ''fenestrae''. ''Mercuriceratops'' was placed in the
Chasmosaurinae 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 ...
. It is the oldest chasmosaurine known from Canada, and the first pre-
Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...
ceratopsid to have been collected on both sides of the Canada–US border. Though the profile of the ''Mercuriceratops'' squamosal suggests it was a transitional form between older rectangular squamosals of
centrosaurine Centrosaurinae (from the Greek, meaning "pointed lizards") is a subfamily of ceratopsid dinosaurs, a group of large quadrupedal ornithischians. Centrosaurine fossil remains are known primarily from the northern region of Laramidia (modern day Al ...
shape and later triangular squamosals, the describers rejected this hypothesis because juvenile centrosaurines do not show such a transitional phase during their
ontogeny Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the stu ...
.


See also

*
Timeline of ceratopsian research This timeline of ceratopsian research is a chronological listing of events in the history of paleontology focused on the ceratopsians, a group of herbivorous marginocephalian dinosaurs that evolved parrot-like beaks, bony frills, and, later, spe ...


References

{{Taxonbar, from=Q16934814 Fossils of Canada Chasmosaurines Late Cretaceous dinosaurs of North America Fossil taxa described in 2014 Taxa named by Philip J. Currie Dinosaur Park fauna Paleontology in Montana Campanian genus first appearances Campanian genus extinctions Ornithischian genera