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''Pachyrhinosaurus'' (meaning in Greek "thick-nosed lizard", from ' (), thick; ' (), nose; and (), lizard) is an extinct genus 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 ...
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 from the Late Cretaceous period of
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 the Car ...
. The first examples were discovered by
Charles M. Sternberg Charles Mortram Sternberg (1885–1981) was an American-Canadian fossil collector and paleontology, paleontologist, son of Charles Hazelius Sternberg. Late in his career, he collected and described ''Pachyrhinosaurus'', ''Brachylophosaurus'', ' ...
in Alberta, Canada, in 1946, and named in 1950. Over a dozen partial skulls and a large assortment of other fossils from various species have been found in Alberta and Alaska. A great number were not available for study until the 1980s, resulting in a relatively recent increase of interest in ''Pachyrhinosaurus''. Three species have been identified. ''P. lakustai'', from the
Wapiti Formation The Wapiti Formation is a geological formation of the Western Canada Sedimentary Basin in northwestern Alberta, and northeastern British Columbia, Canada. Its deposition spanned the time interval from the lower Campanian through to the upper Maast ...
, the bonebed horizon of which is roughly equivalent age to the upper Bearpaw and lower Horseshoe Canyon Formations, is known to have existed from about 73.5–72.5 million years ago. ''P. canadensis'' is younger, known from the lower Horseshoe Canyon Formation, about 71.5–71 Ma ago and the St. Mary River Formation. Fossils of the youngest species, ''P. perotorum'', have been recovered from the Prince Creek Formation of Alaska, and date to 70–69 Ma ago. The presence of three known species makes this genus the most speciose among the centrosaurines.


Discovery and species

''Pachyrhinosaurus canadensis'', was described in 1950 by Charles Mortram Sternberg based on the holotype incomplete skull NMC 8867, and the paratype incomplete skull NMC 8866, which included the anterior part of the skull but was lacking the right lower mandible, and the "beak". These skulls were collected in 1945 and 1946 from the sandy clay of the Horseshoe Canyon Formation in Alberta, Canada. In the years to come, additional material would be recovered at the Scabby Butte locality of the St. Mary River Formation near Lethbridge, Alberta, from terrestrial sediments considered to be between 74 and 66 million years old. These were among the first dinosaur sites found in the province, in the 1880s. The significance of these discoveries was not understood until shortly after World War II when preliminary excavations were conducted. Another ''Pachyrhinosaurus'' skull was taken out of the Scabby Butte locality in 1955, and then in 1957
Wann Langston Jr. Wann Langston Jr. (1921 – April 7, 2013) was an American paleontologist and professor at the University of Texas at Austin. Langston worked on a number of different reptiles and amphibians in his long career, beginning with the 1950 description ...
and a small crew excavated additional pachyrhinosaur remains. The University of Calgary has plans to reopen this important site some day as a field school for university-level paleontology students. Several specimens, NMC 21863, NMC 21864, NMC 10669 assigned in 1975 by W. Langston, Jr. to ''Pachyrhinosaurus'' were also recovered at the Scabby Butte locality. Another ''Pachyrhinosaurus'' bonebed, on the Wapiti River south of Beaverlodge in northwestern Alberta, was worked briefly by staff of the Royal Tyrrell Museum in the late 1980s but is now worked annually for a couple weeks each summer (since 2006) by the University of Alberta. Material from this site appears referable to ''Pachyrhinosaurus canadensis''. In 1974, Grande Prairie, Alberta science teacher Al Lakusta found a large bonebed along
Pipestone Creek Pipestone Creek is a waterway that runs through central Alberta, Canada. For example, over of Pipestone Creek parkland is situated in Millet, Alberta, with a combination of meadows and urban forest. It originates east of Pigeon Lake and flows ea ...
in Alberta. When the area was finally excavated between 1986 and 1989 by staff and volunteers of the
Royal Tyrrell Museum of Palaeontology The Royal Tyrrell Museum of Palaeontology (RTMP, and often referred to as the Royal Tyrrell Museum) is a palaeontology museum and research facility in Drumheller, Alberta, Canada. The museum was named in honour of Joseph Burr Tyrrell, and is situ ...
, paleontologists discovered an amazingly large and dense selection of bones—up to 100 per square meter, with a total of 3,500 bones and 14 skulls. This was apparently the site of a mass mortality, perhaps a failed attempt to cross a river during a flood. Found amongst the fossils were the skeletons of four distinct age groups ranging from juveniles to full-grown dinosaurs, indicating that the ''Pachyrhinosaurus'' cared for their young. The adult skulls had both convex and concave bosses as well as unicorn-style horns on the parietal bone just behind their eyes. The concave boss types might be related to erosion only and not reflect male/female differences. In 2008, a detailed monograph describing the skull of the Pipestone Creek pachyrhinosaur, and penned by
Philip J. 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 ...
,
Wann Langston Jr. Wann Langston Jr. (1921 – April 7, 2013) was an American paleontologist and professor at the University of Texas at Austin. Langston worked on a number of different reptiles and amphibians in his long career, beginning with the 1950 description ...
, and Darren Tanke, classified the specimen as a second species of ''Pachyrhinosaurus'', named ''P. lakustai'' after its discoverer.Currie, P.J., Langston, W., and Tanke, D.H. (2008). "A new species of ''Pachyrhinosaurus'' (Dinosauria, Ceratopsidae) from the Upper Cretaceous of Alberta, Canada." pp. 1-108. In: Currie, P.J., Langston, W., and Tanke, D.H. 2008.
A New Horned Dinosaur from an Upper Cretaceous Bone Bed in Alberta
'. NRC Research Press, Ottawa, Ontario, Canada. 144 pp.
In 2013, Fiorillo ''et al.'' described a new specimen, an incomplete nasal bone attributable to ''Pachyrhinosaurus perotorum'' which was collected from the Kikak-Tegoseak Quarry on the Colville River in Alaska. Fiorillo ''et al.'' named this unique northern Alaskan species after the Texas oil
billionaire A billionaire is a person with a net worth of at least one billion (1,000,000,000, i.e., a thousand million) units of a given currency, usually of a major currency such as the United States dollar, euro, or pound sterling. The American busin ...
and benefactor,
Ross Perot Henry Ross Perot (; June 27, 1930 – July 9, 2019) was an American business magnate, billionaire, politician and philanthropist. He was the founder and chief executive officer of Electronic Data Systems and Perot Systems. He ran an inde ...
. This bone, designated DMNH 21460 belongs to an immature individual. This discovery expands the known age profile of this dinosaur genus from this particular site. The specimen has nasal ornamentation that is dorsally enlarged, representing an intermediate stage of growth. Of note, the authors pointed out that the posterior part of the nasal shows evidence for "a degree of integument complexity not previously recognized in other species" of ''Pachyrhinosaurus''. It was determined that the dorsal surface of the nasal boss bore a thick, cornified pad and sheath.


Description

Size estimates for the largest ''Pachyrhinosaurus'' species, ''P. canadensis'' indicate lengths of and a weight of . The other species, ''P. lakustai'' and ''P. perotorum'', have been estimated by Greg Paul at in length and in weight. They were herbivorous and possessed strong cheek teeth to help them chew tough, fibrous plants. Instead of horns, their skulls bore massive, flattened bosses; a large boss over the nose and a smaller one over the eyes. A prominent pair of horns grew from the frill and extended upwards. The skull also bore several smaller horns or ornaments that varied between individuals and between species. In ''P. canadensis'' and ''P. perotorum'', the bosses over the nose and eyes nearly grew together, and were separated only by a narrow groove. In ''P. lakustai'', the two bosses were separated by a wide gap. In ''P. canadensis'' and ''P. lakustai'', the frill bore two additional small, curved, backward-pointed horns. These were not present in ''P. perotorum'', and in fact some specimens of ''P. lakustai'' also lack them, which may indicate that the presence of these horns varied by age or sex. Various ornaments of the nasal boss have also been used to distinguish between different species of ''Pachyrhinosaurus''. Both ''P. lakustai'' and ''P. perotorum'' bore a jagged, comb-like extension at the tip of the boss which was missing in ''P. canadensis''. ''P. perotorum'' was unique in having a narrow dome in the middle of the back portion of the nasal boss, and ''P. lakustai'' had a pommel-like structure projecting from the front of the boss (the boss of ''P. canadensis'' was mainly flat on top and rounded). ''P. perotorum'' bore two unique, flattened horns which projected forward and down from the top edge of the frill, and ''P. lakustai'' bore another comb-like horn arising from the middle of the frill behind the eyes.


Classification

The cladogram below shows the phylogenetic position of all currently known ''Pachyrhinosaurus'' species following Chiba ''et al.'' (2017):


Paleobiology


Growth rates

During the first few years of development, ''P. perotorum'' show extremely rapid growth. When the animals were one year old, they had already reached 28% of their adult body size. By age two, they were almost half the size of a mature adult. However, the rate of growth slows considerably after that, and maximum size is not fully attained until about age twenty. The development of characteristics useful in sexual selection, including competition between males, such as pronounced
nasal Nasal is an adjective referring to the nose, part of human or animal anatomy. It may also be shorthand for the following uses in combination: * With reference to the human nose: ** Nasal administration, a method of pharmaceutical drug delivery ** ...
bosses, occurred at approximately nine years of age. This presumably corresponds to the age of sexual maturity. Unlike other ''Pachyrhinosaurus'' species, ''P. perotorum'' shows highly conspicuous growth banding in the bones, indicating retarded growth during the winter. This is perhaps not surprising, considering that ''P. perotorum'' experienced much harsher winters than southerly species within the genus. ''P. lakustai'' does not show growth banding early in ontogeny in the specimens that have been examined. However, growth bands are weakly expressed later in ontogeny. This probably indicates rapid growth in youth, followed by gradually decreasing growth rates as the animal neared adulthood. The growth curve of the animal would therefore be somewhat
asymptotic In analytic geometry, an asymptote () of a curve is a line such that the distance between the curve and the line approaches zero as one or both of the ''x'' or ''y'' coordinates tends to infinity. In projective geometry and related contexts, ...
, unlike the linear growth found in many ectothermic animals. The development of characteristics useful in sexual selection, including competition between males, such as pronounced
nasal Nasal is an adjective referring to the nose, part of human or animal anatomy. It may also be shorthand for the following uses in combination: * With reference to the human nose: ** Nasal administration, a method of pharmaceutical drug delivery ** ...
bosses, occurred when the dinosaur was roughly 73% the size of a full-grown adult. The age of sexual maturity is unknown. Due to the lack of conspicuous growth banding, more detailed analyses of ''P. lakustai'' growth rates cannot be performed.


Paleoecology


St. Mary River Formation


Habitat

The St. Mary River Formation has not undergone a definitive radiometric dating, however, the available stratigraphic correlation has shown that this formation was deposited between 74 and 66 million years ago, during the Campanian and the late Maastrichtian, during the final regression of the mid-continental Bearpaw Seaway. It ranges from as far south as Glacier County, Montana to as far north as the Little Bow River in Alberta. The St. Mary River Formation is part of the Western Canadian Sedimentary Basin in southwestern Alberta, which extends from the Rocky Mountains in the west to the
Canadian Shield The Canadian Shield (french: Bouclier canadien ), also called the Laurentian Plateau, is a geologic shield, a large area of exposed Precambrian igneous and high-grade metamorphic rocks. It forms the North American Craton (or Laurentia), the anc ...
in the east. It is laterally equivalent to the Horseshoe Canyon Formation. The region where dinosaurs lived was bounded by mountains to the west, and included ancient channels, small freshwater ponds, streams, and floodplains.


Paleofauna

''Pachyrhinosaurus'' shared its
paleoenvironment Paleoecology (also spelled palaeoecology) is the study of interactions between organisms and/or interactions between organisms and their environments across geologic timescales. As a discipline, paleoecology interacts with, depends on and informs ...
with other dinosaurs, such as 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 Jurassic. ...
ns '' Anchiceratops'' and '' Montanoceratops cerorhynchus'', the armored nodosaur '' Edmontonia longiceps'', the duckbilled hadrosaur ''
Edmontosaurus ''Edmontosaurus'' ( ) (meaning "lizard from Edmonton") is a genus of hadrosaurid (duck-billed) dinosaur. It contains two known species: ''Edmontosaurus regalis'' and ''Edmontosaurus annectens''. Fossils of ''E. regalis'' have been found in rocks ...
regalis'', the theropods ''
Saurornitholestes ''Saurornitholestes'' ("lizard-bird thief") is a genus of carnivorous dromaeosaurid theropod dinosaur from the late Cretaceous of Canada (Alberta) and the United States (Montana, New Mexico, Alabama, North Carolina, and South Carolina). Two spec ...
'' and '' Troodon'', possibly the
ornithopod Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (), that started out as small, bipedal running grazers and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world ...
'' Thescelosaurus'', and the tyrannosaurid '' Albertosaurus'', which was likely the apex predator in its ecosystem. Vertebrates present in the St. Mary River Formation at the time of ''Pachyrhinosaurus'' included the
actinopterygian Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or ho ...
fishes ''Amia fragosa'', '' Lepisosteus'', ''
Belonostomus ''Belonostomus'' (from el, βέλος , 'dart' and el, στόμα 'mouth') is a genus of prehistoric ray-finned fish that was described by Louis Agassiz in 1844. It is a member of the order Aspidorhynchiformes, a group of fish known for their ...
'', '' Paralbula casei'', and '' Platacodon nanus'', the mosasaur '' Plioplatecarpus'', the turtle '' Boremys'' and the diapsid reptile ''
Champsosaurus ''Champsosaurus'' is an extinct genus of crocodile-like choristodere reptile, known from the Late Cretaceous and early Paleogene periods of North America and Europe (Campanian-Paleocene). The name ''Champsosaurus'' is thought to come from , () sa ...
''. A fair number of mammals lived in this region, which included '' Turgidodon russelli'', ''
Cimolestes ''Cimolestes'' (from Ancient Greek , 'chalk robber') is a genus of early eutherians with a full complement of teeth adapted for eating insects and other small animals. Paleontologists have disagreed on its relationship to other mammals, in part b ...
'', ''
Didelphodon ''Didelphodon'' (from ''is''/nowiki>.html" ;"title="/nowiki>''is''/nowiki>">/nowiki>''is''/nowiki> "opossum" plus "tooth") is a genus of stagodont metatherians from the Late Cretaceous of North America. Description Although perhaps little la ...
'', ''
Leptalestes ''Leptalestes'' is an extinct genus of mammals in the infraclass Metatheria. It was described by B.M. Davis in 2007. A new species, ''L. toevsi'', was described from the late Cretaceous period of the United States by John P. Hunter, Ronald E. Hei ...
'', ''
Cimolodon ''Cimolodon'' is a genus of the extinct mammal order of Multituberculata within the suborder Cimolodonta and the family Cimolodontidae. Specimens are known from the Late Cretaceous of North America. Systematics The genus ''Cimolodon'' was nam ...
nitidus'', and ''
Paracimexomys ''Paracimexomys'' is a genus of extinct mammals in the also extinct Multituberculata order. ''Paracimexomys'' lived during the Cretaceous period. The few fossils remains come from North America. Some Romanian fossils were also tentatively assig ...
propriscus''. Non-vertebrates in this ecosystem included mollusks, the oyster '' Crassostrea wyomingensis'', the small clam '' Anomia'', and the snail ''
Thiara ''Thiara'' is a genus of freshwater snails, aquatic gastropod mollusks in the subfamily Thiarinae of the family Thiaridae. Species Species with accepted names within the genus ''Thiara'' include: * † '' Thiara aldrichi'' Palmer, 1944 * ' ...
''. Flora of the region include the aquatic angiosperm '' Trapago angulata'', the amphibious heterosporous fern '' Hydropteris pinnata'',
rhizome In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow hori ...
s, and taxodiaceous conifers.


Horseshoe Canyon Formation


Habitat

The Horseshoe Canyon Formation has been
radiometrically dated Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares t ...
as being between 74 and 67 million years old. It was deposited during the gradual withdrawal of the Western Interior Seaway, during the Campanian and Maastrichtian stage of the Late Cretaceous period. The Horseshoe Canyon Formation is a terrestrial unit which is part of the
Edmonton Group Within the earth science of geology, the Edmonton Group is a Late Cretaceous (Campanian stage) to early Paleocene stratigraphic unit of the Western Canada Sedimentary Basin in the central Alberta plains. It was first described as the Edmonton Forma ...
that includes the
Battle Formation The Battle Formation is a Formation (geology), geologic formation of Late Cretaceous (Maastrichtian) age in the Western Canadian Sedimentary Basin, Western Canada Sedimentary Basin. It is present throughout much of the central Alberta plains, wh ...
and the
Whitemud Member Within the earth science of geology, the Edmonton Group is a Late Cretaceous ( Campanian stage) to early Paleocene stratigraphic unit of the Western Canada Sedimentary Basin in the central Alberta plains. It was first described as the Edmonto ...
, both in Edmonton. The valley where dinosaurs lived included ancient meandering estuary channels, straight channels, peat
swamp A swamp is a forested wetland.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Swamps are considered to be transition zones because both land and water play a role in ...
s, river deltas, floodplains, shorelines and wetlands. Due to the changing sea levels, many different environments are represented in the Horseshoe Canyon Formation, including offshore and near-shore marine habitats and coastal habitats like lagoons, and tidal flats. The area was wet and warm with a temperate to subtropical climate. Just prior to the Campanian–Maastrichtian boundary, the mean annual temperature and precipitation in this region dropped rapidly. The dinosaurs from this formation form part of the
Edmontonian The Edmontonian was a North American faunal epoch occurring during the Late Cretaceous, lasting from approximately 70 to 68 million years ago. Paleobiogeography In southern North America, little changed in the transition from the Judithian to th ...
land vertebrate age, and are distinct from those in the formations above and below. Modern life at high elevations in lower latitudes resembles life at low elevation in higher latitudes. There may be parallels to this phenomenon in Cretaceous ecosystems, for instance, ''Pachyrhinosaurus'' species are found in both Alaska and upland environments in southern Alberta.Lehman, T. M., 2001, Late Cretaceous dinosaur provinciality: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, pp. 310-328. During the
Edmontonian The Edmontonian was a North American faunal epoch occurring during the Late Cretaceous, lasting from approximately 70 to 68 million years ago. Paleobiogeography In southern North America, little changed in the transition from the Judithian to th ...
, in North America's northern biome, there is a general trend of reduced centrosaurine diversity, with only ''Pachyrhinosaurus'' surviving. ''Pachyrhinosaurus'' appears to have been part of a coastal fauna characterized by an association with ''
Edmontosaurus ''Edmontosaurus'' ( ) (meaning "lizard from Edmonton") is a genus of hadrosaurid (duck-billed) dinosaur. It contains two known species: ''Edmontosaurus regalis'' and ''Edmontosaurus annectens''. Fossils of ''E. regalis'' have been found in rocks ...
''.


Paleofauna

''P. canadensis'' coexisted with
ankylosaurids Ankylosauridae () is a family of armored dinosaurs within Ankylosauria, and is the sister group to Nodosauridae. The oldest known Ankylosaurids date to around 122 million years ago and went extinct 66 million years ago during the Cretaceous–Pal ...
'' Anodontosaurus lambei'' and '' Edmontonia longiceps'', the maniraptorans ''
Atrociraptor ''Atrociraptor'' (meaning "savage thief") is a genus of saurornitholestine dromaeosaurid theropod dinosaur from the Late Cretaceous (Maastrichtian stage) of Alberta, Canada. The type (and only) specimen of ''Atrociraptor'', holotype RTMP 95.1 ...
marshalli'', ''
Epichirostenotes ''Epichirostenotes'' (meaning "above ''Chirostenotes''", because it lived after the latter genus) is a genus of oviraptorosaurian dinosaur from the late Cretaceous. ''Epichirostenotes'' is known from an incomplete skeleton found in 1923 at the ...
curriei'', the troodontid ''
Albertavenator ''Albertavenator'' (meaning "Alberta hunter") is a genus of small troodontid theropod dinosaur, known from the early Maastrichtian in the Cretaceous period. It contains a single species, ''A. curriei'', named after paleontologist Phil Currie, bas ...
'' curriei, the alvarezsaurid theropod '' Albertonykus borealis'', the
ornithomimids Ornithomimidae (meaning "bird-mimics") is a family of theropod dinosaurs which bore a superficial resemblance to modern ostriches. Ornithomimids were fast, omnivorous or herbivorous dinosaurs known mainly from the Late Cretaceous Period of Lauras ...
''
Dromiceiomimus ''Dromiceiomimus'' is a genus of ornithomimid theropod from the Late Cretaceous (early Maastrichtian) of Alberta, Canada. The type species, ''D. brevitertius'', is considered a synonym of ''Ornithomimus edmontonicus'' by some authors, while other ...
brevitertius'', ''
Ornithomimus ''Ornithomimus'' (; "bird mimic") is a genus of ornithomimid dinosaurs from the Late Cretaceous Period of what is now North America. ''Ornithomimus'' was a swift bipedal theropod which fossil evidence indicates was covered in feathers, equipped w ...
edmontonicus'', and an unnamed species of '' Struthiomimus'', the bone-head pachycephalosaurids '' Stegoceras'', and '' Sphaerotholus edmontonensis'', the
ornithopod Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (), that started out as small, bipedal running grazers and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world ...
''
Parksosaurus ''Parksosaurus'' (meaning " William Parks's lizard") is a genus of neornithischian dinosaur from the early Maastrichtian-age Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada. It is based on most of a partially articulated skeleton a ...
warreni'', the
hadrosaurids Hadrosaurids (), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod family, which includ ...
''
Edmontosaurus ''Edmontosaurus'' ( ) (meaning "lizard from Edmonton") is a genus of hadrosaurid (duck-billed) dinosaur. It contains two known species: ''Edmontosaurus regalis'' and ''Edmontosaurus annectens''. Fossils of ''E. regalis'' have been found in rocks ...
regalis'', ''
Hypacrosaurus ''Hypacrosaurus'' (meaning "near the highest lizard" reek υπο-, ''hypo-'' = less + ακρος, ''akros'', high because it was almost but not quite as large as ''Tyrannosaurus'') was a genus of duckbill dinosaur similar in appearance to ''Co ...
altispinus'', and ''
Saurolophus ''Saurolophus'' (; meaning "lizard crest") is a genus of large hadrosaurid dinosaur from the Late Cretaceous period of Asia and North America, that lived in what is now the Horseshoe Canyon and Nemegt formations about 70 million to 68 million ...
osborni'', 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 Jurassic. ...
ns '' Anchiceratops ornatus'', '' Arrhinoceratops brachyops'', '' Eotriceratops xerinsularis'', '' Montanoceratops cerorhynchus'', and the
tyrannosaurids Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family (biology), family of coelurosaurian Theropoda, theropod dinosaurs that comprises two subfamilies containing up to thirteen genus, genera, including the eponymous ''Tyrannos ...
'' Albertosaurus'' sarcophagus and a possible species of ''
Daspletosaurus ''Daspletosaurus'' ( ; meaning "frightful lizard") is a genus of tyrannosaurid dinosaur that lived in Laramidia between about 79.5 and 74 million years ago, during the Late Cretaceous Period. The genus ''Daspletosaurus'' contains three species ...
'', which were the apex predators of this paleoenvironment. Of these, the hadrosaurs dominated in terms of sheer number and made up half of all dinosaurs who lived in this region. Vertebrates present in the Horseshoe Canyon Formation at the time of ''Pachyrhinosaurus'' included
reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...
s, and
amphibian Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...
s. Sharks, rays,
sturgeon Sturgeon is the common name for the 27 species of fish belonging to the family Acipenseridae. The earliest sturgeon fossils date to the Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretace ...
s,
bowfin The bowfin (''Amia calva'') is a bony fish, native to North America. Common names include mudfish, mud pike, dogfish, grindle, grinnel, swamp trout, and choupique. It is regarded as a relict, being the sole surviving species of the Halecomorphi ...
s, gars and the gar-like ''
Belonostomus ''Belonostomus'' (from el, βέλος , 'dart' and el, στόμα 'mouth') is a genus of prehistoric ray-finned fish that was described by Louis Agassiz in 1844. It is a member of the order Aspidorhynchiformes, a group of fish known for their ...
'' made up the fish fauna. Reptiles such as turtles and crocodilians are rare in the Horseshoe Canyon Formation, and this was thought to reflect the relatively cool climate which prevailed at the time. A study by Quinney et al. (2013) however, showed that the decline in turtle diversity, which was previously attributed to climate, coincided instead with changes in soil drainage conditions, and was limited by aridity, landscape instability, and migratory barriers. The saltwater
plesiosaur The Plesiosauria (; Greek: πλησίος, ''plesios'', meaning "near to" and ''sauros'', meaning "lizard") or plesiosaurs are an order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia. Plesiosaurs first appeared ...
''
Leurospondylus ''Leurospondylus'' is a genus of plesiosaur whose family is currently disputed, but is suggested to be Plesiosauridae. Etymology The name ''Leurospondylus'' comes from a fusion of two Greek words, ''leuros'' (λευρός) meaning "even", "fla ...
'' was present and freshwater environments were populated by turtles, ''
Champsosaurus ''Champsosaurus'' is an extinct genus of crocodile-like choristodere reptile, known from the Late Cretaceous and early Paleogene periods of North America and Europe (Campanian-Paleocene). The name ''Champsosaurus'' is thought to come from , () sa ...
'', and crocodilians like '' Leidyosuchus'' and ''
Stangerochampsa ''Stangerochampsa'' is an extinct genus of globidontan alligatoroid, possibly an alligatorine or a stem-caiman, from the Late Cretaceous of Alberta. It is based on RTMP.86.61.1, a skull, partial lower jaws, and partial postcranial skeleton di ...
''. Evidence has shown that multituberculates and the early marsupial ''
Didelphodon ''Didelphodon'' (from ''is''/nowiki>.html" ;"title="/nowiki>''is''/nowiki>">/nowiki>''is''/nowiki> "opossum" plus "tooth") is a genus of stagodont metatherians from the Late Cretaceous of North America. Description Although perhaps little la ...
coyi'' were present. Vertebrate trace fossils from this region included the tracks of theropods, ceratopsians and ornithopods, which provide evidence that these animals were also present.Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. (2004) 861 pp. . Non-vertebrates in this ecosystem included both marine and terrestrial invertebrates.


See also

* Timeline of ceratopsian research


References

{{Portal bar, Dinosaurs, Cretaceous, Canada, Alaska Centrosaurines Late Cretaceous dinosaurs of North America Maastrichtian life Taxa named by Charles Mortram Sternberg Fossil taxa described in 1950 Horseshoe Canyon fauna Paleontology in Alberta Paleontology in Alaska Campanian genus first appearances Maastrichtian genus extinctions Ornithischian genera