''Brachyceratops'' ('short horned face') is a

dubious Doubt is a mental state in which the mind remains suspended between two or more contradictory propositions, unable to be certain of any of them. Doubt on an emotional level is indecision between belief and disbelief. It may involve uncertainty ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

ceratopsian Ceratopsia or Ceratopia ( or ; Ancient Greek, Greek: "horned faces") is a group of herbivore, herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period (geology), Period, although anc ...

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 only from partial juvenile specimens dating to the late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

Period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

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 Columb ...

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

. ''Brachyceratops'' has historically been known from juvenile remains, with one specimen having since been re-classified as ''

Rubeosaurus ovatus ''Styracosaurus'' ( ; meaning "spiked lizard" from the Ancient Greek / "spike at the butt-end of a spear-shaft" and / "lizard") is a genus of herbivorous ceratopsian dinosaur from the Cretaceous Period (Campanian stage), about 75.5 to 74.5&nb ...

''.Andrew T. McDonald & John R. Horner, (2010). "New Material of "Styracosaurus" ovatus from the Two Medicine Formation of Montana", In: Michael J. Ryan, Brenda J. Chinnery-Allgeier, and David A. Eberth (eds), ''New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium'', Indiana University Press, 656 pp.

History of discovery

''Brachyceratops montanensis'', 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 specime ...

, was first discovered in the

Two Medicine Formation The Two Medicine Formation is a geological formation, or rock body, in northwestern Montana and southern Alberta that was deposited between and (million years ago), during Campanian (Late Cretaceous) time. It crops out to the east of the Rocky M ...

(

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. Campani ...

, about 74 million years old) on a Blackfoot Indian Reservation in Teton County in north-central

."Brachyceratops." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. ''The Age of Dinosaurs''. Publications International, LTD. p. 133. . The original find was made on August 1913 by C. W. Gilmore and his assistant John Floyd Strayer and was named and shortly described by Gilmore one year later. The generic name is derived from el, βραχύς, ''brachys'', "short", el, κέρας, ''keras'', "horn" and el, ὤψ, ''ops'', "face", in reference to the short snout. The specific name refers to the provenance from Montana. All that was found were incomplete and jumbled remains of five juvenile individuals of about 1.5 m (5 feet) in length. It has been speculated that these juveniles may have been nest mates that stayed together after hatching. 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 sever ...

specimen is USNM 7951, a partial skull. The

paratype In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype nor a syntype). O ...

s are USNM 7952, a snout, USNM 7953, a partial skeleton with skull and USNM 7957, a foot. The material is disarticulated but the preservation is excellent. In 1917 Gilmore published a monograph on ''Brachyceratops'' in which a reconstruction of the skeleton as a whole was given. In 1939 Gilmore referred a larger subadult specimen, USNM 14765, to ''Brachyceratops''. All specimens are currently part of the collection of the

Smithsonian Institution The Smithsonian Institution ( ), or simply the Smithsonian, is a group of museums and education and research centers, the largest such complex in the world, created by the U.S. government "for the increase and diffusion of knowledge". Founded ...

Washington D.C. ) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle, Jefferson Memorial, White House, Adams Morgan, Na ...

, where a skeletal restoration is mounted. As ''Brachyceratops'' is known only from the remains of five juveniles — plus the subadult that Gilmore found about a mile from the original specimens —, it was long considered likely that these represented the immature forms of known centrosaurine

s, with ''

Monoclonius ''Monoclonius'' (meaning "single sprout") is a dubious genus of herbivorous ceratopsian dinosaur found in the Late Cretaceous layers of the Judith River Formation in Montana, United States, and the uppermost rock layers of the Dinosaur Park Form ...

'' often suggested as the likeliest candidate. By 2011 however, several studies had shown that the single specimen which was adult enough to be compared with related species, USNM 14765, represented the juvenile form of the later-named '' Rubeosaurus''.

Description

Among the five original specimens parts of three skulls were discovered, detached from their owner's body and fragmented. Despite this, the skull showed that the animal had only small bumps over the eyes rather than full-grown horns like in the more famous

ceratopsians Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic ...

such as ''

Triceratops ''Triceratops'' ( ; ) is a genus of herbivorous chasmosaurine ceratopsid dinosaur that first appeared during the late Maastrichtian stage of the Late Cretaceous period, about 68 million years ago in what is now North America. It is one ...

''. The nasal horn was thick and low, while its neck frill was moderately large. Unfortunately the specimens were incomplete so it cannot be determined if there were parietal openings in the frill like some other

possessed.

Classification

''Brachyceratops'' belonged to the

Centrosaurinae 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 A ...

, but its exact placement has been difficult to discover because it is known only from juvenile specimens. In 1997, Scott Sampson and colleagues re-examined ''Brachyceratops'' and noted that it is almost certainly the juvenile form of an already known centrosaurine dinosaur. However, because many features that distinguish ceratopsians from each other do not appear until adulthood, exactly which centrosaurine remained unknown, and Sampson ''et al.'' classified ''Brachyceratops'' as a ''nomen dubium'', or dubious name.Sampson, S.D., M. J. Ryan, and D. H. Tanke. (1997). "Craniofacial ontogeny in centrosaurine dinosaurs (Ornithischia: Ceratopsidae): taphonomic and behavioral implications." ''Zoological Journal of the Linnean Society'', 121: 293–337. In 2007, Michael J. Ryan and colleagues suggested that ''Brachyceratops'' was possibly the juvenile form of ''Styracosaurus ovatus'', which has since been reclassified as '' Rubeosaurus''. A 2011 study supported this idea for the most mature specimen of ''Brachyceratops'', USNM 14765, which shows one unique newly evolved feature ( apomorphy) in common with ''Rubeosaurus'' to the exclusion of other centrosaurines. However, the same study suggested that because the holotype specimen of ''Brachyceratops'' is too incomplete and juvenile to preserve any determinable apomorphies, ''Brachyceratops'' must be considered a nomen dubium, and cannot be a senior synonym of ''Rubeosaurus''.

References

{{Taxonbar, from=Q131602 Centrosaurines Late Cretaceous dinosaurs of North America Nomina dubia Fossil taxa described in 1914 Paleontology in Montana Taxa named by Charles W. Gilmore Campanian genus first appearances Campanian genus extinctions Ornithischian genera

History of discovery

Description

Classification

See also

References