Scolosaurus Temporal range: Late Cretaceous, | |
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Skeletal mount of the S. thronus holotype at the Royal Tyrell Museum | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | † Ornithischia |
Clade: | † Thyreophora |
Clade: | † Ankylosauria |
Family: | † Ankylosauridae |
Subfamily: | † Ankylosaurinae |
Tribe: | † Ankylosaurini |
Genus: | † Scolosaurus Nopcsa, 1928 |
Type species | |
†Scolosaurus cutleri | |
Other species | |
Synonyms | |
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Scolosaurus is an extinct genus of ankylosaurid dinosaurs within the subfamily Ankylosaurinae. It is known from the lower levels of the Dinosaur Park Formation and upper levels of the Oldman Formation in the Late Cretaceous (latest middle Campanian stage, about 76.5 Ma ago) of Alberta, Canada. It contains two species, S. cutleri and S. thronus. [2] [1] The type species, S. cutleri, measured up to 5.6 metres (18 ft) in length and 2.2 metric tons (2.4 short tons) in body mass. [3]
Scolosaurus was named by Franz Nopcsa von Felső-Szilvás in 1928, based on holotype NHMUK PV 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. [2] [4] It was collected from the bottom of the Dinosaur Park Formation in fine-grained sandstone and fine-grained claystone sediments that were deposited during the Campanian stage of the Late Cretaceous period, approximately 76.5 million years ago. [5] The holotype specimen is housed in the collection of the Natural History Museum in London, England.
In 2013, Arbour 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, which has been dated at approximately 74 million years. [6] The remains were collected in 1986-1987 in grey siltstone that was deposited during the Campanian stage of the Cretaceous period. [5] The specimen is housed in the collection of the Museum of the Rockies in Bozeman, Montana.
The generic name Scolosaurus means "pointed stake lizard" and is derived from the Greek words skolos (σκῶλος) meaning "pointed stake", and saûros (σαύρα) meaning "lizard". [7] The specific name, cutleri, honours its discoverer and the collector of the holotype, W. E. Cutler, [4] who was seriously injured when the specimen fell on him as he was excavating it. [8]
In 1928, Nopcsa assigned the specimen to the family Ankylosauridae, and drew morphological comparisons with the fossil material known from Dyoplosaurus . In 1971, Walter Coombs concluded that there was only one species of ankylosaurid during the Campanian age of the Late Cretaceous of North America. He synonymized the species Anodontosaurus lambei , Dyoplosaurus acutosquameus , and Scolosaurus cutleri with Euoplocephalus tutus but did not provide any justification for these synonymies. [9] 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 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 of their cervical armour, the details of other armour and the structure of the forelimb. They also concluded that Scolosaurus and Dyoplosaurus are distinct, due to differences noted in the pelvis and armour. [2] 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. [10] However, this synonymization is contentious as Oohkotokia was subsequently recognized as valid. [11] Thus, much of the material illustrated as belonging to Scolosaurus may actually pertain to Oohkotokia.
The following cladogram is based on a 2015 phylogenetic analysis 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, 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: [12]
The following cladogram is based on a 2017 phylogenetic analysis 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: [13]
In 1874, G. M. Dawson excavated specimen USNM 7943 at the Milk River locality of the Frenchman Formation in Alberta. It was collected from terrestrial sediments that are considered to be from the Maastrichtian 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 Currie who conducted a detailed phylogenetic analysis of the ankylosauridae. [14] 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, Montana. [15] 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 scapulae, both ilia, partial ischia, and both femora, both tibiae and fibulae.
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:
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. [16] 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 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 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. [17] [18] Below this formation are the nearshore deposits of the Virgelle Sandstone. Lithologies, invertebrate 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 horizons of the upper Two Medicine are evidence of at least seasonally arid conditions.
Scolosaurus shared its paleoenvironment with other dinosaurs, such as the duck-billed hadrosaurs Hypacrosaurus , Acristavus , Gryposaurus , Brachylophosaurus , Glishades , Prosaurolophus and Maiasaura , and the ankylosaur Edmontonia . [19] Volcanic eruptions 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. [20] A large variety of ceratopsians coexisted in this region, which included Achelousaurus , Brachyceratops , Cerasinops , Einiosaurus , Prenoceratops and Rubeosaurus . Carnivores included an unnamed troodontid, possibly Stenonychosaurus , the dromaeosaurs Bambiraptor and Saurornitholestes , and the large tyrannosaurids Daspletosaurus and Gorgosaurus . [21]
The excellent vertebrate 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 are represented, including sharks, rays, sturgeons, gars and others. This region preserves the remains of many aquatic amphibians and reptiles, including bivalves, gastropods, frogs, salamanders, turtles, Champsosaurus and crocodilians. Terrestrial lizards, including whiptails, skinks, monitors and alligator lizards have also been discovered. Pterosaurs 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 dromaeosaur 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. [22]
Ankylosaurus is a genus of armored dinosaur. Its fossils have been found in geological formations dating to the very end of the Cretaceous Period, about 68–66 million years ago, in western North America, making it among the last of the non-avian dinosaurs. It was named by Barnum Brown in 1908; it is monotypic, containing only A. magniventris. The generic name means "fused" or "bent lizard", and the specific name means "great belly". A handful of specimens have been excavated to date, but a complete skeleton has not been discovered. Though other members of Ankylosauria are represented by more extensive fossil material, Ankylosaurus is often considered the archetypal member of its group, despite having some unusual features.
Euoplocephalus is a genus of large herbivorous ankylosaurid dinosaurs, living during the Late Cretaceous of Canada. It has only one named species, Euoplocephalus tutus.
Zuul is a genus of herbivorous ankylosaurine dinosaur from the Campanian Judith River Formation of Montana. The type species is Zuul crurivastator. It is known from a complete skull and tail, which represents the first ankylosaurin known from a complete skull and tail club, as well as the most complete ankylosaurid specimen thus far recovered from North America. The specimen also preserved in situ osteoderms, keratin, and skin remains.
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–Paleogene extinction event. These animals were mainly herbivorous and were obligate quadrupeds, with leaf-shaped teeth and robust, scute-covered bodies. Ankylosaurids possess a distinctly domed and short snout, wedge-shaped osteoderms on their skull, scutes along their torso, and a tail club.
Anodontosaurus is an extinct genus of ankylosaurid dinosaurs within the subfamily Ankylosaurinae. It is known from the entire span of the Late Cretaceous Horseshoe Canyon Formation of southern Alberta, Canada, and is also known from the Dinosaur Park Formation. It contains two species, A. lambei and A. inceptus.
Dyoplosaurus is a monospecific genus of ankylosaurid dinosaur from Alberta that lived during the Late Cretaceous in what is now the Dinosaur Park Formation. Dyoplosaurus represents a close relative of Scolosaurus and Anodontosaurus, two ankylosaurids known from the Horseshoe Canyon and Dinosaur Park Formation.
Panoplosaurus is a genus of armoured dinosaur from the Late Cretaceous of Alberta, Canada. Few specimens of the genus are known, all from the middle Campanian of the Dinosaur Park Formation, roughly 76 to 75 million years ago. It was first discovered in 1917, and named in 1919 by Lawrence Lambe, named for its extensive armour, meaning "well-armoured lizard". Panoplosaurus has at times been considered the proper name for material otherwise referred to as Edmontonia, complicating its phylogenetic and ecological interpretations, at one point being considered to have existed across Alberta, New Mexico and Texas, with specimens in institutions from Canada and the United States. The skull and skeleton of Panoplosaurus are similar to its relatives, but have a few significant differences, such as the lumpy form of the skull osteoderms, a completely fused shoulder blade, and regularly shaped plates on its neck and body lacking prominent spines. It was a quadrupedal animal, roughly 5 m (16 ft) long and 1,600 kg (3,500 lb) in weight. The skull has a short snout, with a very domed surface, and bony plates directly covering the cheek. The neck had circular groups of plates arranged around the top surface, both the forelimb and hindlimb were about the same length, and the hand may have only included three fingers. Almost the entire surface of the body was covered in plates, osteoderms and scutes of varying sizes, ranging from large elements along the skull and neck, to smaller, round bones underneath the chin and body, to small ossicles that filled in the spaces between other, larger osteoderms.
Tarchia is a genus of herbivorous ankylosaurid dinosaur from the late Cretaceous of Mongolia.
Nodocephalosaurus is a monospecific genus of ankylosaurid dinosaur from New Mexico that lived during the Late Cretaceous in what is now the De-na-zin member of the Kirtland Formation. The type and only species, Nodocephalosaurus kirtlandensis, is known only from a partial skull. It was named in 1999 by Robert M. Sullivan. Nodocephalosaurus has an estimated length of 4.5 metres and weight of 1.5 tonnes. It is closely related and shares similar cranial anatomy to Akainacephalus.
Palaeoscincus is a dubious genus of ankylosaurian dinosaur based on teeth from the mid-late Campanian-age Upper Cretaceous Judith River Formation of Montana. Like several other dinosaur genera named by Joseph Leidy, it is an historically important genus with a convoluted taxonomy that has been all but abandoned by modern dinosaur paleontologists. Because of its wide use in the early 20th century, it was somewhat well known to the general public, often through illustrations of an animal with the armor of Edmontonia and the tail club of an ankylosaurid.
The Two Medicine Formation is a geological formation, or rock body, in northwestern Montana and southern Alberta that was deposited between 82.4 Ma and 74.4 Ma, during Campanian time. It crops out to the east of the Rocky Mountain Overthrust Belt, and the western portion of this formation is folded and faulted while the eastern part, which thins out into the Sweetgrass Arch, is mostly undeformed plains. Below the formation are the nearshore deposits of the Virgelle Sandstone, and above it is the marine Bearpaw Shale. Throughout the Campanian, the Two Medicine Formation was deposited between the western shoreline of the Late Cretaceous Interior Seaway and the eastward advancing margin of the Cordilleran Overthrust Belt. The Two Medicine Formation is mostly sandstone, deposited by rivers and deltas.
Heishansaurus, meaning "Heishan lizard" after the area in China where it was discovered, is the name given to a dubious genus of herbivorous ornithischian dinosaur, probably belonging to the Ankylosauridae.
Shanxia is a monospecific genus of ankylosaurid dinosaur from the Shanxi Province that lived during the Late Cretaceous in what is now the Huiquanpu Formation. Shanxia may possibly represent a junior synonym of Tianzhenosaurus, an ankylosaurine also known from the Huiquanpu Formation of China.
Minotaurasaurus is a monospecific genus of ankylosaurid dinosaur that lived in Mongolia during the Late Cretaceous in what is now the Djadochta Formation. The type and only species, Minotaurasaurus ramachandrani, is known from two skulls, a cervical vertebra and a cervical half ring. It was named and described in 2009 by Clifford Miles and Clark Miles. The first fossils of Minotaurasaurus were illegally exported out of Mongolia.It has been suggested to be a synonym of Tarchia but more recent publications consider it as a distinct genus.
Ahshislepelta is a monospecific genus of ankylosaur dinosaur from New Mexico that lived during the Late Cretaceous in what is now the Hunter Wash Member of the Kirtland Formation. The type and only species, Ahshislepelta minor, is known only from an incomplete postcranial skeleton of a small subadult or adult individual. It was named in 2011 by Michael Burns and Robert M. Sullivan. Based on the size of the humerus, Ahshislepelta is larger than Pinacosaurus mephistocephalus but smaller than Talarurus and Pinacosaurus grangeri.
Oohkotokia is a genus of ankylosaurid dinosaur within the subfamily Ankylosaurinae. It is known from the upper levels of the Two Medicine Formation of Montana, United States. The discovery of Oohkotokia supports that Ankylosaurine dinosaurs existed and flourished continuously in Montana and/or Alberta throughout the late Campanian and early Maastrichtian stages in the Late Cretaceous period. It was a large, heavily built, quadrupedal, herbivore, that could grow up to 5 metres (16 ft) long and weigh up to 2 metric tons.
Ziapelta is an extinct genus of ankylosaurid. Its fossils have been found in the Hunter Wash and De-na-zin members of the Kirtland Formation of Upper Cretaceous (Campanian) New Mexico. It was named in 2014, in a research paper led by ankylosaur researcher Victoria Arbour. There is a single species in the genus, Ziapelta sanjuanensis. The genus is named after the Zia sun symbol, a stylized sun with four groups of rays, having religious significance to the Zia people of New Mexico, and the iconic symbol on the state flag of New Mexico, and pelta (Latin), a small shield, in reference to the osteoderms found on all ankylosaurids. The specific name is in reference to San Juan County and the San Juan basin, where the fossils were found. Multiple specimens have been described to date, though the fossils are mostly from the front part of the animal. Its closest relative appears to be either Scolosaurus or Nodocephalosaurus, depending on what cladistic model is used.
This timeline of ankylosaur research is a chronological listing of events in the history of paleontology focused on the ankylosaurs, quadrupedal herbivorous dinosaurs who were protected by a covering bony plates and spikes and sometimes by a clubbed tail. Although formally trained scientists did not begin documenting ankylosaur fossils until the early 19th century, Native Americans had a long history of contact with these remains, which were generally interpreted through a mythological lens. The Delaware people have stories about smoking the bones of ancient monsters in a magic ritual to have wishes granted and ankylosaur fossils are among the local fossils that may have been used like this. The Native Americans of the modern southwestern United States tell stories about an armored monster named Yeitso that may have been influenced by local ankylosaur fossils. Likewise, ankylosaur remains are among the dinosaur bones found along the Red Deer River of Alberta, Canada where the Piegan people believe that the Grandfather of the Buffalo once lived.
Platypelta is an extinct genus of herbivorous ankylosaurid dinosaurs within the subfamily Ankylosaurinae. It is known from the Late Cretaceous Dinosaur Park Formation of southern Alberta, Canada. The type species is Platypelta coombsi.
Akainacephalus is a monospecific genus of ankylosaurid dinosaur from southern Utah that lived during the Late Cretaceous in what is now the Horse Mountain Gryposaur Quarry of the Kaiparowits Formation. The type and only species, Akainacephalus johnsoni, is known from the most complete ankylosaur specimen ever discovered from southern Laramidia, including a complete skull, tail club, a number of osteoderms, limb elements and part of its pelvis, among other remains. It was described in 2018 by Jelle P. Wiersma and Randall B. Irmis. It is closely related and shares similar cranial anatomy to Nodocephalosaurus.