''Scolosaurus'' 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 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 ankylosaurid

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 ...

s within the subfamily

Ankylosaurinae Ankylosaurinae is a subfamily of ankylosaurid dinosaurs, existing from the Early Cretaceous about 105 million years ago until the end of the Late Cretaceous, about 66 mya. Many genera are included in the clade, such as ''Ankylosaurus'', ''Pina ...

. It is known from the lower levels of the

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. ...

and upper levels of the Oldman Formation in 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'', ...

(latest middle

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 ...

stage, about 76.5 Ma ago) 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 T ...

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 ...

. It contains two

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

, ''S. cutleri'' and ''S. thronus''. The type species, ''S. cutleri'', measured up to in length and in body mass.

Discovery

''Scolosaurus'' was named by Franz Nopcsa von Felső-Szilvás in

1928 Events January * January – British bacteriologist Frederick Griffith reports the results of Griffith's experiment, indirectly proving the existence of DNA. * January 1 – Eastern Bloc emigration and defection: Boris Bazhano ...

, based on

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 ...

NHMUK R.5161, a nearly complete specimen that preserves the entire skeleton except for the distal end of the tail, the right forelimb, the right hindlimb, and the skull. The rare preservation of osteoderms and skin impression are also present. The fossil skeleton was discovered by William Edmund Cutler, an independent fossil collector in 1914 at Quarry 80 of the Deadlodge Canyon locality. It was collected from the bottom of the

in fine-grained sandstone and fine-grained claystone sediments that were deposited during the

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 ...

period, approximately 76.5 million years ago. The holotype specimen is housed in the collection of the

Natural History Museum A natural history museum or museum of natural history is a scientific institution with natural history collections that include current and historical records of animals, plants, fungi, ecosystems, geology, paleontology, climatology, and more. ...

London London is the capital and List of urban areas in the United Kingdom, largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary dow ...

, England. In 2013,

Arbour Arbor(s) or Arbour(s) may refer to: Arts and entertainment * ''Arbor'' (installation), a 2013 public artwork in Indianapolis, Indiana, US * Arbor, a counterweight-carrying device found in theater fly systems * ''The Arbor'', a 1980 play by Andr ...

and Currie reassigned specimen MOR 433, upon which the genus ''Oohkotokia'' was based, to ''Scolosaurus''. This specimen consists of a partial skull, both humeri, a caudal vertebra and several osteoderms and was recovered in the Upper Member of the Two Medicine Formation, in

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 ...

, which has been dated at approximately 74 million years. The remains were collected in 1986-1987 in grey siltstone that was deposited during the

stage of the

period. The specimen is housed in the collection of the

Museum of the Rockies Museum of the Rockies is a museum in Bozeman, Montana. Originally affiliated with Montana State University in Bozeman, and now also, the Smithsonian Institution, the museum is largely known for its paleontological collections. The Museum houses ...

Bozeman, Montana Bozeman is a city and the county seat of Gallatin County, Montana, United States. Located in southwest Montana, the 2020 census put Bozeman's population at 53,293, making it the fourth-largest city in Montana. It is the principal city o ...

. The generic name ''Scolosaurus'' means "pointed stake lizard" and is derived from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

words ''skolos'' (σκῶλος) meaning "pointed stake", and ''saûros'' (σαύρα) meaning "lizard". The specific name, ''cutleri'', honours its discoverer and the collector of the

, W. E. Cutler, who was seriously injured when the specimen fell on him as he was excavating it.

Classification

In 1928, Nopcsa assigned the specimen to the family

Ankylosauridae 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–Pa ...

, and drew morphological comparisons with the fossil material known from '' Dyoplosaurus''. In 1971,

Walter Coombs Walter may refer to: People * Walter (name), both a surname and a given name * Little Walter, American blues harmonica player Marion Walter Jacobs (1930–1968) * Gunther (wrestler), Austrian professional wrestler and trainer Walter Hahn (born 19 ...

concluded that there was only one species of ankylosaurid during the

age of the Late Cretaceous of North America. He synonymized the species '' Anodontosaurus lambei'', ''

Dyoplosaurus acutosquameus ''Dyoplosaurus'' (meaning “double-armoured lizard”) is a monospecific genus of ankylosaurid dinosaur from Alberta that lived during the Late Cretaceous (middle Campanian, ~76.5–75 Ma) in what is now the Dinosaur Park Formation. ''Dyoplosau ...

'', and ''Scolosaurus cutleri'' with ''

Euoplocephalus tutus ''Euoplocephalus'' ( ) is a genus of very large, herbivorous ankylosaurid dinosaurs, living during the Late Cretaceous of Canada. It has only one named species, ''Euoplocephalus tutus''. The first fossil of ''Euoplocephalus'' was found in 1897 ...

'' but did not provide any justification for these synonymies.Coombs W. (1971) The Ankylosauridae. Ph.D. thesis, Columbia University, New York, NY, 487 p. The synonymization of ''Scolosaurus cutleri'' and ''Euoplocephalus tutus'' was generally accepted and thus NHMUK R.5161 was assigned to ''E. tutus''. However, a redescription of ''Scolosaurus'' published in 2013 in the ''

Canadian Journal of Earth Sciences The ''Canadian Journal of Earth Sciences'' is a monthly peer-reviewed scientific journal established in 1963, which reports current research on all aspects of the Earth sciences. It is published by NRC Research Press. The journal also publishes ...

'' by Paul Penkalski and William T. Blows suggested that the genus is a valid taxon. They concluded that ''Scolosaurus'' can be distinguished from ''Euoplocephalus'' by the

form Form is the shape, visual appearance, or configuration of an object. In a wider sense, the form is the way something happens. Form also refers to: *Form (document), a document (printed or electronic) with spaces in which to write or enter data * ...

of their cervical armour, the details of other

armour Armour (British English) or armor (American English; see spelling differences) is a covering used to protect an object, individual, or vehicle from physical injury or damage, especially direct contact weapons or projectiles during combat, or f ...

and the structure of the forelimb. They also concluded that ''Scolosaurus'' and ''Dyoplosaurus'' are distinct, due to differences noted in the

pelvis The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...

and armour. Due to its completeness, the holotype of ''Scolosaurus'' has formed the basis for most ''Euoplocephalus'' reconstructions since 1971; therefore, most images of ''Euoplocephalus'' actually depict ''Scolosaurus'' instead. A 2013 study found that the ankylosaurine '' Oohkotokia'' was indistinguishable from ''Scolosaurus'', and was therefore considered a

junior synonym The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linn ...

. However, this synonymization is contentious as ''Oohkotokia'' was subsequently recognized as valid. Thus, much of the material illustrated as belonging to ''Scolosaurus'' may actually pertain to ''Oohkotokia''.

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 ...

is based on a 2015

phylogenetic analysis In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

of the Ankylosaurinae conducted by Victoria Arbour and Phillip J. Currie. The cladogram follows the biogeographical family tree provided by that study, which is a fusion of the study's 50% majority rule tree as well as the maximum agreement subtree. The study's 50% majority rule tree was a cladogram formed by a collection of

clades A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English te ...

, although it only included clades that appear in more than 50% of the family trees found during the analysis. The maximum agreement subtree is the cladogram that results from an algorithm which attempts to maximize the amount of taxa included in the result while also retaining the fundamental shape of all other trees in the sample. Some controversial taxa thus had to be omitted by the subtree in order for the resulting cladogram to fulfill the second requirement. The biogeographical tree (i.e. the following cladogram) is basically the 50% majority rule tree, except with some of the polytomies resolved according to the results of the maximum agreement subtree: The following

is based on a 2017

of the Ankylosaurinae conducted by Victoria Arbour and David Evans. The cladogram depicts the majority rule (average result) of 10 most parsimonious trees, which each are considered to have the fewest evolutionary steps, thus being the most accurate under the principle of

Occam's razor Occam's razor, Ockham's razor, or Ocham's razor ( la, novacula Occami), also known as the principle of parsimony or the law of parsimony ( la, lex parsimoniae), is the problem-solving principle that "entities should not be multiplied beyond neces ...

Referred material

In 1874, G. M. Dawson excavated specimen USNM 7943 at the Milk River locality of the

Frenchman Formation The Frenchman Formation is stratigraphic unit of Late Cretaceous (late Maastrichtian) age in the Western Canada Sedimentary Basin. It is present in southern Saskatchewan and the Cypress Hills of southeastern Alberta. The formation was defined b ...

in Alberta. It was collected from terrestrial sediments that are considered to be from the

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, approximately 70.6 to 66 million years old. The specimen consisted of a partial first cervical ring, which is part of the dinosaur's neck. In 2013, this material was assigned to ''Scolosaurus'' by Arbour and Curry who conducted a detailed phylogenetic analysis of the ankylosauridae. It is currently housed at the Smithsonian Institution in Washington, DC. In 1928, George F. Sternberg, collected specimen USNM 11892, from the '' Montanazhdarcho'' holotype locality, high up in the Two Medicine Formation in

Glacier County Glacier County is located in the U.S. state of Montana. As of the 2020 census, the population was 13,778. The county is located in northwestern Montana between the Great Plains and the Rocky Mountains, known to the Blackfeet as the "Backbone ...

. The material, a partial skull, was recovered from channel sandstone sediments that were deposited during the Campanian stage, approximately 74 million years ago. This is also housed at the Smithsonian Institution. Other referred specimens include FPDM V-31, NSM PV 20381 and TMP 2001.42.9. FPDM V-31 and TMP 2001.42.9 are both skulls, in various states of preservation. NSM PV 20381 includes a skull, dorsal vertebrae, caudal vertebrae, ribs, both

scapula The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on eith ...

e, both ilia, partial

ischia Ischia ( , , ) is a volcanic island in the Tyrrhenian Sea. It lies at the northern end of the Gulf of Naples, about from Naples. It is the largest of the Phlegrean Islands. Roughly trapezoidal in shape, it measures approximately east to ...

, and both femora, both

tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it conn ...

e and

fibula The fibula or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity ...

Distinguishing anatomical features

A differential diagnosis is a statement of the anatomical features of an organism (or group) that collectively distinguish it from all other organisms. Some, but not all, of the features in a diagnosis are also autapomorphies. An autapomorphy is a distinctive anatomical feature that is unique to a given organism. According to Arbour and Currie (2013), ''Scolosaurus'' (including the Two Medicine material) can be distinguished from other ankylosaurines based on the following characteristics: * the

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 ...

horns are proportionately longer, are backswept, and have distinct apices (unlike ''Anodontosaurus lambei'' and ''Euoplocephalus tutus'') * the presence of a small circular caputegula at the bases of the squamosal and quadratojugal bones (unlike ''Euoplocephalus tutus'') * the postacetabular process of the ilium is proportionately longer (compared to ''Anodontosaurus lambei'', ''Dyoplosaurus acutosquameus'' and ''Euoplocephalus tutus'') * the presence of proportionately large circular medial osteoderms with low central prominences, and compressed, half-moon shaped lateral/distal osteoderms on the cervical half rings (unlike ''Anodontosaurus lambei'' and ''Euoplocephalus tutus'') * the sacral ribs are laterally-directed (unlike ''Dyoplosaurus acutosquameus'') * the osteoderms are conical, with centrally positioned apices on the lateral sides of the anterior portion of the tail (unlike ''Dyoplosaurus acutosquameus'') * the tail club knob appears circular in dorsal view, unlike that of ''Anodontosaurus'', which appears wider than it is long or that of ''Dyoplosaurus'', which appears longer than it is wide * the presence of anteriorly-directed nares, and the absence of a continuous keel between the squamosal horn and the supraorbital bones (unlike ''Ankylosaurus magniventris'')

Paleoecology

Habitat

Argon-argon radiometric dating indicates that the Two Medicine Formation was deposited between 83.5 and 70.6 million years ago, during the Campanian stage of the Late Cretaceous period, in what is now northwestern Montana. If ''Oohkotokia'' is the same as ''Scolosaurus'' it would mean that ''Scolosaurus'' existed for around 3 million years. The Two Medicine Formation correlates to the Belly River Group in southwest Alberta, and the Pakowki Formation eastward. The Two Medicine Formation was deposited by rivers and deltas between the western shoreline of the

Western Interior Seaway The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, and the Western Interior Sea) was a large inland sea that split the continent of North America into two landmasses. The ancient sea ...

and the eastward advancing margin of the Cordilleran Overthrust Belt. Since the mid-Cretaceous, North America had been divided in half by this seaway, with much of Montana and Alberta below the surface of the water. However, the uplift of the

Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico ...

forced the seaway to retreat eastwards and southwards. Rivers flowed down from the mountains and drained into the seaway, carrying sediment that formed the Two Medicine Formation and the Judith River Group. About 73 million years ago, the seaway began to advance westwards and northwards again, and the entire region was covered by the Bearpaw Sea, now preserved throughout the Western US and Canada by the massive Bearpaw Shale, which overlies the Two Medicine. Below this formation are the nearshore deposits of the Virgelle Sandstone. Lithologies,

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

faunas, and plant and pollen data support that the Two Medicine Formation was deposited in a seasonal, semi-arid climate with possible rainshadows from the Cordilleran highlands. This region experienced a long dry season and warm temperatures. The extensive red beds and

caliche Caliche () is a sedimentary rock, a hardened natural cement of calcium carbonate that binds other materials—such as gravel, sand, clay, and silt. It occurs worldwide, in aridisol and mollisol soil orders—generally in arid or semiarid regions ...

horizons of the upper Two Medicine are evidence of at least seasonally arid conditions.

Paleofauna

''Scolosaurus'' shared its paleoenvironment with other dinosaurs, such as the duck-billed

hadrosaurs 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 incl ...

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 ...

'', ''

Acristavus ''Acristavus'' (meaning "non-crested grandfather") is a genus of saurolophine dinosaur. Fossils have been found from the Campanian Two Medicine Formation in Montana and Wahweap Formation in Utah, United States. The type species ''A. gagslarsoni ...

'', ''

Gryposaurus ''Gryposaurus'' (meaning "hooked-nosed (Greek ''grypos'') lizard"; sometimes incorrectly translated as "griffin (Latin ''gryphus'') lizard") was a genus of duckbilled dinosaur that lived about 80 to 75 million years ago, in the Late Cretaceo ...

'', ''

Brachylophosaurus ''Brachylophosaurus'' ( or ; meaning "short-crested lizard", Greek ''brachys'' = short + ''lophos'' = crest + ''sauros'' = lizard, referring to its small crest) was a mid-sized member of the hadrosaurid family of dinosaurs. It is known from sev ...

'', '' Glishades'', ''

Prosaurolophus ''Prosaurolophus'' (; meaning "before ''Saurolophus''", in comparison to the later dinosaur with a similar head crest) is a genus of hadrosaurid (or duck-billed) dinosaur from the Late Cretaceous of North America. It is known from the remains of ...

'' and ''

Maiasaura ''Maiasaura'' (from the Greek ''μαῖα'', meaning "good mother" and ''σαύρα'', the feminine form of ''saurus'', meaning "reptile") is a large herbivorous saurolophine hadrosaurid ("duck-billed") dinosaur genus that lived in the area cur ...

'', and the ankylosaur ''

Edmontonia ''Edmontonia'' is a genus of panoplosaurin nodosaurid dinosaur from the Late Cretaceous Period. It is part of the Nodosauridae, a family within Ankylosauria. It is named after the Edmonton Formation (now the Horseshoe Canyon Formation in Ca ...

''.

Volcanic eruption Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are oft ...

s from the west periodically blanketed the region with ash, resulting in large-scale mortality, while simultaneously enriching the soil for future plant growth. Fluctuating sea levels also resulted in a variety of other environments at different times and places within the Judith River Group, including offshore and nearshore marine habitats, coastal wetlands, deltas and lagoons, in addition to the inland floodplains. The Two Medicine Formation was deposited at higher elevations farther inland than the other two formations. A large variety of

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 ...

coexisted in this region, which included '' Achelousaurus'', ''

Brachyceratops ''Brachyceratops'' ('short horned face') is a dubious genus of ceratopsian dinosaur known only from partial juvenile specimens dating to the late Cretaceous Period of Montana, United States. ''Brachyceratops'' has historically been known from j ...

'', ''

Cerasinops ''Cerasinops'' (meaning 'cherry face') was a small ceratopsian dinosaur. It lived during the Campanian of the late Cretaceous Period.

'', ''

Einiosaurus ''Einiosaurus'' is a genus of herbivorous centrosaurine ceratopsian dinosaur from the Upper Cretaceous (Campanian stage) of northwestern Montana. The name means 'buffalo lizard', in a combination of Blackfeet Indian ''eini'' and Latinized Ancie ...

'', ''

Prenoceratops ''Prenoceratops'', (meaning 'bent or prone-horned face' and derived from Greek ''prene-/πρηνη-'' meaning 'bent forwards' or 'prone', ''cerat-/κερατ-'' meaning 'horn' and ''-ops/ωψ'' meaning 'face') is a genus of ceratopsian dinosaur f ...

'' and '' Rubeosaurus''. Carnivores included an unnamed troodontid, possibly ''

Stenonychosaurus ''Stenonychosaurus'' (meaning "narrow claw lizard") is a genus of troodontid dinosaur from the Late Cretaceous Dinosaur Park Formation of Alberta, Canada, as well as possibly the Two Medicine Formation. The type and only species, ''S. inequ ...

'', the

dromaeosaur Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...

s '' Bambiraptor'' and '' Saurornitholestes'', and the large tyrannosaurids '' Daspletosaurus'' and ''

Gorgosaurus ''Gorgosaurus'' ( ; ) is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period (Campanian), between about 76.6 and 75.1 million years ago. Fossil remains have been found in the Ca ...

''."3.11 Montana, United States; 2. Lower Two Medicine Formation," in Weishampel, et al. (2004). The excellent

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...

fossil record of Two Medicine and Judith River rocks resulted from a combination of abundant animal life, periodic natural disasters, and the deposition of large amounts of sediment. Many types of freshwater and

estuarine fish Coastal fish, also called inshore fish or neritic fish, inhabit the sea between the shoreline and the edge of the continental shelf. Since the continental shelf is usually less than deep, it follows that pelagic coastal fish are generally ep ...

are represented, including

shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachi ...

rays Ray may refer to: Fish * Ray (fish), any cartilaginous fish of the superorder Batoidea * Ray (fish fin anatomy), a bony or horny spine on a fin Science and mathematics * Ray (geometry), half of a line proceeding from an initial point * Ray (gra ...

, sturgeons,

gar Gars are members of the family Lepisosteidae, which are the only surviving members of the Ginglymodi, an ancient holosteian group of ray-finned fish, which first appeared during the Triassic, over 240 million years ago. Gars comprise seven livin ...

s and others. This region preserves the remains of many aquatic amphibians and reptiles, including bivalves,

gastropods The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. The ...

frog A frog is any member of a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-frog" ''Triadobatrachus'' is ...

salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All t ...

turtle Turtles are an order of reptiles known as Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked t ...

s, ''

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 , () ...

'' and

crocodilia Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period ( Cenomanian stage) and are the closest livi ...

ns. Terrestrial lizards, including whiptails, skinks, monitors and

alligator lizards An alligator lizard is any one of various species of lizards in the family Anguidae that have some shared characteristics. The term may specifically refer to: Species of the genus ''Elgaria'': * Northern alligator lizard (''Elgaria coerulea'') ...

have also been discovered.

Pterosaur Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 ...

s like '' Montanazhdarcho'' and '' Piksi'' as well as birds like '' Apatornis'' and '' Avisaurus'' flew overhead. Several varieties of mammals, such as the multituberculate '' Cimexomys'' coexisted with dinosaurs in the Two Medicine Formation and the various other formations that make up the Judith River wedge. Fossilized eggs belonging to a

have been recovered here. When water was plentiful, the region could support a great deal of plant and animal life, but periodic droughts often resulted in mass mortality.

References

{{Taxonbar, from=Q7434319 Ankylosaurids Late Cretaceous dinosaurs of North America Fossil taxa described in 1928 Taxa named by Franz Nopcsa von Felső-Szilvás Dinosaur Park fauna Oldman fauna Paleontology in Alberta Fossils of Canada Cretaceous Canada Paleontology in Montana Campanian genus first appearances Campanian genus extinctions Ornithischian genera

Discovery

Classification

Referred material

Distinguishing anatomical features

Paleoecology

Habitat

Paleofauna

See also

References