''Sphaerotholus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

pachycephalosaur Pachycephalosauria (; from Greek παχυκεφαλόσαυρος for 'thick headed lizards') is a clade of ornithischian dinosaurs. Along with Ceratopsia, it makes up the clade Marginocephalia. With the exception of two species, most pachyc ...

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 ...

from the Upper

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 th ...

of the western

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

and

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 tot ...

. To date, three

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 appropriate s ...

have been described: 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 specimen ...

, ''S. goodwini'', from the Den-na-zin Member of the

Kirtland Formation The Kirtland Formation (originally the Kirtland Shale) is a sedimentary geological formation. Description The Kirtland Formation is the product of alluvial muds and overbank sand deposits from the many channels draining the coastal plain that ...

(Late

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. Campanian s ...

) of San Juan County,

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Tiguex , OfficialLang = None , Languages = English, Spanish ( New Mexican), Navajo, Ker ...

, USA; ''S. buchholtzae'', from the

Hell Creek Formation The Hell Creek Formation is an intensively studied division of mostly Upper Cretaceous and some lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana. The formation stretches over portions of ...

(Late

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 interval from ...

) of western Carter County,

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 Columbi ...

, USA and 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 by ...

Saskatchewan Saskatchewan ( ; ) is a Provinces and territories of Canada, province in Western Canada, western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on t ...

; and ''S. edmontonensis'', from 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 the ...

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 Ter ...

History of discovery

The

etymology Etymology ()The New Oxford Dictionary of English (1998) – p. 633 "Etymology /ˌɛtɪˈmɒlədʒi/ the study of the class in words and the way their meanings have changed throughout time". is the study of the history of the Phonological chan ...

of ''Sphaerotholus'' is a combination of 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 ...

''sphaira'', meaning "ball", and ''tholos'', meaning "dome", and is a reference to the characteristically dome-shaped pachycephalosaurian

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, the ...

. The survival of ''Sphaerotholus'' from the Campanian of New Mexico to the end of the Maastrichtian of Montana demonstrates that this

taxon In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

had both a relatively long duration (approximately 7-8 million years) and a widespread distribution. Williamson and Carr, who first described the

in 2002, diagnose it as follows: "Differs from all other pachycephalosaurids where known in the possession of a parietosquamosal bar that decreases in depth laterally as seen in caudal view and is bordered by a single row of nodes and one lateroventral corner node." ''Sphaerotholus'' is considered a highly

derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...

pachycephalosaur.

Species

''Sphaerotholus goodwini''

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 several ...

of the type species (NMMNH P-27403, New Mexico Museum of Natural History) consists of an incomplete skull lacking the facial and palatal elements. The species is diagnosed as follows: "''Sphaerotholus'' which in caudal view possesses a parietosquamosal bar that reduces in depth laterally to a lesser extent than in ''S. buchholtzae'' and the parietal is reduced to a thin slip between 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 The quadratojugal is a skull bone present in many vertebrates, including ...

s." The species name honors

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

Mark Goodwin for his work with pachycephalosaurian dinosaurs.

''Sphaerotholus buchholtzae''

The

of ''S. buchholtzae'' (TMP 87.113.3) consists of an incomplete skull. The species was diagnosed as having a parietal that is widely exposed between the squamosals and wide enough to bear parietosquamosal nodes, a shallower caudal margin of the parietosquamosal shelf, the

lateral Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction *Lateral cricoarytenoid muscle *Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral cons ...

corner node is reduced in size and located above the ventral margin of the parietosquamosal bar, and the nodes in the lateral margin of the parietosquamosal shelf reduced on the squamosal and coalescing into a ridge on the postorbital. The specific name honors Emily A. Buchholtz for her extensive work with pachycephalosaurians. Sullivan (2003) considered ''S. buchholtzae'' a junior synonym of ''

Prenocephale ''Prenocephale'' (meaning "sloping head") is a genus of small pachycephalosaurid dinosaur from the Late Cretaceous Nemegt Formation of Mongolia. It was similar in many ways to its close relative, ''Homalocephale''. Description Adult ''Prenoceph ...

edmontonensis'' (or ''Sphaerotholus edmontonensis''). However, Mallon et al. (2015), in their description of a new ''S. buchholtzae'' specimen from the

, noted that ''S. edmontonensis'' was distinct from ''S. buchholtzae'' based on comparative morphology and morphometrics.

''Sphaerotholus edmontonensis''

A ''Troodon edmontonensis'' was described by Brown and Schlaikjer in 1943 on the basis of three domes from the Horseshoe Canyon Formation of Alberta. Williamson and Carr considered the species to be invalid, but in 2010 Nicholas Longrich et al. named a ''Sphaerotholus edmontonensis'' that could be distinguished from ''S. goodwini'' by the paired hornlets on the back of the dome, and from ''S. buchholtzae'' by the elongate parietals. It was once considered a species of ''

Stegoceras ''Stegoceras'' is a genus of pachycephalosaurid (dome-headed) dinosaur that lived in what is now North America during the Late Cretaceous period, about 77.5 to 74 million years ago (mya). The first specimens from Alberta, Canada, were descri ...

'' and was about the same size, reaching in length and in body mass.

References

Sources

External links

dinosaur.net.cn
(includes photograph of the type skull of ''Sphaerotholus goodwini'' and a life restoration of same) {{Taxonbar, from=Q134104 Late Cretaceous dinosaurs of North America Hell Creek fauna Fossil taxa described in 2002 Pachycephalosaurs Horseshoe Canyon fauna Kirtland fauna Paleontology in New Mexico Paleontology in Montana Paleontology in Alberta Campanian genus first appearances Maastrichtian genus extinctions Ornithischian genera