''Arrhinoceratops'' (meaning "no nose-horn face", derived from the

Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic pe ...

"a-/α-" "no", rhis/ῥίς "nose" "keras/κέρας" "horn", "-ops/ὤψ" "face") is a

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 ...

of herbivorous

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 ...

. The name was coined as its original describer concluded it was special because the nose-horn was not a separate bone, however further analysis revealed this was based on a misunderstanding. It lived during the latest

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 ...

/earliest

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 inte ...

stage of 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 ...

, predating its famous relative ''

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 ...

'' by a few million years, although it was contemporary with ''

Anchiceratops ''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-siz ...

''. Its remains have been found in

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...

Discoveries and species

Described by William Arthur Parks in 1925, ''Arrhinoceratops'' is known from a partially crushed, slightly distorted

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...

which lacked the

lower jaw In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

s. The remains were collected from the Neill's Ranch site, along the

Red Deer River The Red Deer River is a river in Alberta and a small portion of Saskatchewan, Canada. It is a major tributary of the South Saskatchewan River and is part of the larger Saskatchewan-Nelson system that empties into Hudson Bay. Red Deer River h ...

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 T ...

by a 1923 expedition from the

University of Toronto The University of Toronto (UToronto or U of T) is a public research university in Toronto, Ontario, Canada, located on the grounds that surround Queen's Park. It was founded by royal charter in 1827 as King's College, the first institution ...

.Parks, W.A. (1925). "''Arrhinoceratops brachyops'', a new genus and species of Ceratopsia from the Edmonton Formation of Alberta". ''University of Toronto Studies, Geology Series'' 19:1-15 Parks named 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 specim ...

''Arrhinoceratops brachyops''. The generic name is derived from Greek α~, "without", ῥίς, ''rhis'', "nose", κέρας, ''keras'', "horn", and ὤψ, ''ops'', "face" as Parks had established that no separate nose-horn was present. The specific name means "short-faced" from Greek βραχύς, ''brachys'', "short". 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 seve ...

is ROM 796 (earlier ROM 5135), which was found in a layer of the

Horseshoe Canyon Formation The Horseshoe Canyon Formation is a stratigraphic unit of the Western Canada Sedimentary Basin in southwestern Alberta. It takes its name from Horseshoe Canyon, an area of badlands near Drumheller. The Horseshoe Canyon Formation is part of th ...

dating from the latest Campanian or perhaps earliest

. It consists of the original skull. Other material from

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its ...

, found in the 1930s, was posthumously named ''Arrhinoceratops? utahensis'' by

Charles Whitney Gilmore Charles Whitney Gilmore (March 11, 1874 – September 27, 1945) was an American paleontologist who gained renown in the early 20th century for his work on vertebrate fossils during his career at the United States National Museum (now the N ...

in 1946. It is based on holotype USNM 15583. The question mark indicates that Gilmore himself had doubts about the identification. In 1976, Douglas A. Lawson transferred the species to '' Torosaurus'', as a ''Torosaurus utahensis''.Hunt, R.K. and Lehman, T.M. (2008). "Attributes of the ceratopsian dinosaur ''Torosaurus'', and new material from the Javelina Formation (Maastrichtian) of Texas". ''Journal of Paleontology'' 82(6): 1127-1138. Apart from the holotype skull little fossil material of ''Arrhinoceratops brachyops'' has been found. In 1981

Helen Tyson Helen may refer to: People * Helen of Troy, in Greek mythology, the most beautiful woman in the world * Helen (actress) (born 1938), Indian actress * Helen (given name), a given name (including a list of people with the name) Places * Helen, G ...

in a revision of the genus, provisionally referred specimen ROM 1439,Tyson, H., 1981, "The structure and relationships of the horned dinosaur ''Arrhinoceratops'' Parks (Ornithischia: Ceratopsidae)", ''Canadian Journal of Earth Sciences'' 18: 1241-1247 but in 2007

Andrew Farke Andrew is the English form of a given name common in many countries. In the 1990s, it was among the top ten most popular names given to boys in English-speaking countries. "Andrew" is frequently shortened to "Andy" or "Drew". The word is derived ...

moved this to ''Torosaurus''.

Description

Since this dinosaur is known only from its skull, scientists have few data about its overall anatomy. The skull, as restored, features a broad, square, neck frill with two oval shaped openings. The frill is deeply veined on both the top and the underside by arterial grooves. The sides of the frill are adorned by about nine osteoderms. The rear edge of the frill is lightly scalloped. The left

squamosal 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 ...

in the frill side of the holotype shows a pathological opening, perhaps the result of a wound. Its brow horns were moderately long, but its nose horn was shorter and blunter than most ceratopids. The snout is short and high. Its body is assumed to be typical of the Ceratopsidae. Based on the skull some popular-science books estimate the body length to be long when fully grown. In 2010, Gregory S. Paul estimated its length at , its weight at .Paul, G.S., 2010, ''The Princeton Field Guide to Dinosaurs'', Princeton University Press p. 267 Already

Richard Swann Lull Richard Swann Lull (November 6, 1867 – April 22, 1957) was an American paleontologist and Sterling Professor at Yale University who is largely remembered now for championing a non-Darwinian view of evolution, whereby mutation(s) could ...

had in 1933 been politely critical of Parks' original description, and Tyson discovered that Parks, an

entomologist Entomology () is the scientific study of insects, a branch of zoology. In the past the term "insect" was less specific, and historically the definition of entomology would also include the study of animals in other arthropod groups, such as ara ...

, had made many mistakes. The most notable of these was that the very trait the genus was named after, the lack of a separate ossification or ''os epinasale'' for the nose-horn, is in fact normal for the ceratopids, in which group this horn is an outgrowth of the

nasal bone The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose. Ea ...

, not a distinct element. Other incorrect observations by Parks included the conclusion that the ''os rostrale'', the bone core of the upper beak, directly touched the nasals instead of being separated from them by the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...

e; a presumed anterior process of the

jugal The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Anatomy ...

touching the premaxilla; and thinking that the interparietal bar of the frill presented a separate skeletal element, an ''os interparietale''.

Phylogeny

''Arrhinoceratops'' was by Parks placed within the

Ceratopsia 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 Jurass ...

(this name is Ancient Greek for "horned faces"), a group of herbivorous dinosaurs with

parrot Parrots, also known as psittacines (), are birds of the roughly 398 species in 92 genera comprising the order Psittaciformes (), found mostly in tropical and subtropical regions. The order is subdivided into three superfamilies: the Psittacoide ...

-like beaks which thrived in

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

and

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...

during the Cretaceous Period, which ended roughly 66 million years ago. In 1930 Lori Russell refined this to the Ceratopsidae. Tyson concluded it was closely related to ''Torosaurus'', probably even its direct ancestor."Arrhinoceratops." 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. 127. . Modern research indicates that ''Arrhinoceratops'' is a member of 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, durin ...

.P. Dodson and P.J. Currie, 1990, "Neoceratopsia". In: D.B. Weishampel, H. Osmolska, and P. Dodson (eds.), ''The Dinosauria''. First Edition. University of California Press, Berkeley, pp 593-618

Cladistic Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...

analyses recover it close to ''

''.

The following

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

shows the

phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological s ...

of ''Arrhinoceratops'' according to a study by

Scott Sampson Scott Donald Sampson (born April 22, 1961) is a Canadian paleontologist and science communicator. Sampson is currently the Executive Director of California Academy of Sciences in San Francisco, California. He was previously Vice President of Res ...

e.a. in 2010.

Paleobiology

''Arrhinoceratops'' lived in a wet coast-land with warm summers but cool winters. It was likely preyed upon by '' Albertosaurus''. ''Arrhinoceratops'', like all ceratopsians, was a

herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...

. During the Cretaceous, flowering plants were "geographically limited on the landscape", and so it is likely that this dinosaur fed on the predominant plants of the era: ferns, cycads and conifers. It would have used its sharp ceratopsian beak to bite off the leaves or needles. Its

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

was densely forested.

Footnotes

References