Sphaerotholus
Encyclopedia
Sphaerotholus is a genus
of pachycephalosaurid dinosaur
from the Upper Cretaceous
of the western United States
. To date, two species
have been described: the type species
, S. goodwini, from the Den-na-zin Member of the Kirtland Formation
(Late Campanian
) of San Juan County
, New Mexico
, and a second species, S. buchholtzae, from the Hell Creek Formation
(Late Maastrichtian
) of western Carter County
, Montana
. The etymology
of Sphaerotholus is a combination of the Greek
sphaira, meaning "ball," and tholos, meaning "dome," and is a reference the characteristically dome-shaped pachycephalosaurian skull
. The survival of Sphaerotholus from the Campanian of New Mexico to the end of the Maastrichtian of Montana demonstrates that this taxon
had both a relatively long duration (approximately 7-8 million years) and a widespread distribution. Williamson and Carr (2002) diagnose this genus
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
pachycephalosaur.
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 by Carr and Williamson (2002) 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
s." The species name honors paleontologist Mark Goodwin for his work with pachycephalosaurian dinosaurs. A second specimen was referred to cf. S. goodwini (NMMNH P-30068), from the younger Farmington Member of the Kirtland Formation. It consists of a fragmentary squamosal and almost complete dentary, and another unidentified skull fragment.
of S. buchholtzae (TMP 87.113.3) consists of an incomplete skull. The species is diagnosed by Carr and Williamson (2002) as follows: "Sphaerotholus which in caudal view possesses a parietal that is widely exposed between the squamosals that is wide enough to bear parietosquamosal nodes , the caudal margin of the parietosquamosal shelf shallows to a greater degree than in S. goodwini, the lateral corner node is reduced in size relative to S. goodwini and located above the ventral margin of the parietosquamosal bar, and the nodes in the lateral margin of the parietosquamosal shelf are reduced on the squamosal and coalesce into a ridge on the postorbital." The species name honors Emily A. Buchholtz for her extensive work with pachycephalosaurians.
It has been proposed that this species could be a subjective junior synonym of P. edmontonensis (or Sphaerotholus edmontonense).
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of pachycephalosaurid dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
from the Upper Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
of the western United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. To date, two species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
have been described: the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
, S. goodwini, from the Den-na-zin Member of the Kirtland Formation
Kirtland Formation
The Kirtland Formation is a sedimentary geological formation. It is the product of alluvial muds and overbank sand deposits from the many channels draining the coastal plain that existed on the inland seashore of North America, in the late Cretaceous period. It overlies the Fruitland Formation...
(Late Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
) of San Juan County
San Juan County, New Mexico
-2010:Whereas according to the 2010 U.S. Census Bureau:*51.6% White*0.6% Black*36.6% Native American*0.4% Asian*0.1% Native Hawaiian or Pacific Islander*3.5% Two or more races*7.2% Other races*19.1% Hispanic or Latino -2000:...
, New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
, and a second species, S. buchholtzae, from the Hell Creek Formation
Hell Creek Formation
The Hell Creek Formation is an intensely-studied division of Upper Cretaceous to lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana...
(Late Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
) of western Carter County
Carter County, Montana
-Demographics:As of the census of 2000, there were 1,360 people, 543 households, and 382 families residing in the county. The population density was -Demographics:...
, Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
. The etymology
Etymology
Etymology is the study of the history of words, their origins, and how their form and meaning have changed over time.For languages with a long written history, etymologists make use of texts in these languages and texts about the languages to gather knowledge about how words were used during...
of Sphaerotholus is a combination of the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
sphaira, meaning "ball," and tholos, meaning "dome," and is a reference the characteristically dome-shaped pachycephalosaurian skull
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
. The survival of Sphaerotholus from the Campanian of New Mexico to the end of the Maastrichtian of Montana demonstrates that this taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
had both a relatively long duration (approximately 7-8 million years) and a widespread distribution. Williamson and Carr (2002) diagnose this genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
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
Anatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
view and is bordered by a single row of nodes and one lateroventral corner node." Sphaerotholus is considered a highly derived
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
pachycephalosaur.
Sphaerotholus goodwini
The holotypeHolotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
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 by Carr and Williamson (2002) 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
Parietal
Parietal may refer to:*Parietal placentation*Parietal lobe of the brain*Parietal bone of the skull*Parietal scales of a snake lie in the general region of the parietal bone*Parietal cell in the stomach*Parietal pleura...
is reduced to a thin slip between the squamosal
Squamosal
The squamosal is a bone of the head of higher vertebrates. It is the principal component of the cheek region in the skull, lying below the temporal series and otic notch and bounded anteriorly by postorbital. Posteriorly, the squamosal articulates with the posterior elements of the palatal complex,...
s." The species name honors paleontologist Mark Goodwin for his work with pachycephalosaurian dinosaurs. A second specimen was referred to cf. S. goodwini (NMMNH P-30068), from the younger Farmington Member of the Kirtland Formation. It consists of a fragmentary squamosal and almost complete dentary, and another unidentified skull fragment.
Sphaerotholus buchholtzae
The holotypeHolotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
of S. buchholtzae (TMP 87.113.3) consists of an incomplete skull. The species is diagnosed by Carr and Williamson (2002) as follows: "Sphaerotholus which in caudal view possesses a parietal that is widely exposed between the squamosals that is wide enough to bear parietosquamosal nodes , the caudal margin of the parietosquamosal shelf shallows to a greater degree than in S. goodwini, the lateral corner node is reduced in size relative to S. goodwini and located above the ventral margin of the parietosquamosal bar, and the nodes in the lateral margin of the parietosquamosal shelf are reduced on the squamosal and coalesce into a ridge on the postorbital." The species name honors Emily A. Buchholtz for her extensive work with pachycephalosaurians.
It has been proposed that this species could be a subjective junior synonym of P. edmontonensis (or Sphaerotholus edmontonense).
External links
- Sphaerotholus at Thescelosaurus!
- dinosaur.net.cn (includes photograph of the type skull of Sphaerotholus goodwini and a life restoration of same)