Amtocephale
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''Amtocephale'' is a
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of pachycephalosaurid
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
from early
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent 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 ''cre ...
(
Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...
-
Coniacian The Coniacian is an age or stage in the geologic timescale. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series and spans the time between 89.8 ± 1 Ma and 86.3 ± 0.7 Ma (million years ago). The Coniacian is preceded by ...
stages) deposits of southern
Gobi Desert The Gobi Desert (, , ; ) is a large, cold desert and grassland region in North China and southern Mongolia. It is the sixth-largest desert in the world. The name of the desert comes from the Mongolian word ''gobi'', used to refer to all of th ...
,
Mongolia Mongolia is a landlocked country in East Asia, bordered by Russia to the north and China to the south and southeast. It covers an area of , with a population of 3.5 million, making it the world's List of countries and dependencies by po ...
. ''Amtocephale'' is known from the
holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...
MPC-D 100/1203, a nearly complete frontoparietal dome of a subadult individual. It was collected from the Baynshire Formation at the Amtgai locality. ''Amtocephale'' was first named by Mahito Watabe, Khishigjaw Tsogtbaatar and Robert M. Sullivan in
2011 The year marked the start of a Arab Spring, series of protests and revolutions throughout the Arab world advocating for democracy, reform, and economic recovery, later leading to the depositions of world leaders in Tunisia, Egypt, and Yemen ...
and the
type species In International_Code_of_Zoological_Nomenclature, 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 spe ...
is ''Amtocephale gobiensis''. The generic name combines a reference to the Amtgai site with a Greek κεφαλή, ''kephale'', "head". The
specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...
refers to the provenance from the Gobi. ''Amtocephale'' was assigned to the
Pachycephalosauridae 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 pachycepha ...
and is perhaps the oldest pachycephalosaurid known, depending on the exact age of the formation.


History of naming

Paleontological expeditions of the Hayashibara Museum of Natural Sciences with the
Mongolian Paleontological Center Mongolian may refer to: * Something of, from, or related to Mongolia, a country in Asia * Mongolian people, or Mongols * Bogd Khanate of Mongolia, the government of Mongolia, 1911–1919 and 1921–1924 * Mongolian language * Mongolian alphabet * ...
into the
Gobi Desert The Gobi Desert (, , ; ) is a large, cold desert and grassland region in North China and southern Mongolia. It is the sixth-largest desert in the world. The name of the desert comes from the Mongolian word ''gobi'', used to refer to all of th ...
began in 1993, surveying and prospecting in over 50 localities. The Amtgai locality, an outcrop of fossil beds within small cliffs, was excavated in 1993, 1994, 2001 and 2004. This small bed of less than of exposed
sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...
and
mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...
is part of the Baynshire Formation, where the HMNS and MPC collected and limb bones of
ornithopods Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (). They represent one of the most successful groups of herbivore, herbivorous dinosaurs during the Cretaceous. The most primitive members of the group were bipedal and rel ...
,
turtle Turtles are reptiles of the order (biology), order Testudines, characterized by a special turtle shell, shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Crypt ...
skulls and shells, several specimens of the
theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...
''
Segnosaurus ''Segnosaurus'' is a genus of therizinosaurid dinosaur that lived in what is now southeastern Mongolia during the Late Cretaceous, about 102–86 million years ago. Multiple incomplete but well-preserved specimens were discovered in the Go ...
'', and the skull of a
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 pachycepha ...
. This single partial subadult skull of ''Amtocephale'' from the Baynshire Formation, MPC-D 100/1203, was described by Japanese paleontologist Mahito Watabe, Mongolian paleontogist Khishigjaw Tsogtbaatar, and American paleontologist Robert M. Sullivan in
2011 The year marked the start of a Arab Spring, series of protests and revolutions throughout the Arab world advocating for democracy, reform, and economic recovery, later leading to the depositions of world leaders in Tunisia, Egypt, and Yemen ...
as the new taxon ''Amtocephale gobiensis''. The
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
name is a combination of the Amtgai locality and the
Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...
word κεφαλή (''cephalo'') for "head", while the
species name In taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, altho ...
is a reference to the Gobi Desert of Mongolia where it was found. The age of the Baynshire Formation is poorly constrained, correlated to some stage of the early
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent 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 ''cre ...
between the
Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...
and the Santonian, though it has even been found to be as young as the
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. Campa ...
(~80.6 mya). Review of the land-vertebrate faunas of Mongolia has been inconclusive as the fauna are not distinctive, but as it is from the Baynshire Formation ''Amtocephale'' would correlate with a "Baynshirenian" age. The vertebrates of the Baynshire Formation suggest the Amtgai locality is no younger than the Santonian (83.5 mya) but it may be slightly older. This makes ''Amtocephale'' approximately the same age as the fauna of the
Milk River Formation The Milk River Formation is a sandstone-dominated stratigraphic unit of the Western Canada Sedimentary Basin in southern Alberta, Canada. It was deposited in near-shore to coastal environments during Late Cretaceous (late Santonian to early Campa ...
of
Alberta Alberta is a Provinces and territories of Canada, province in Canada. It is a part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to its west, Saskatchewan to its east, t ...
. Recent
calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
U–Pb measurements performed by Kurumada and colleagues in 2020 have estimated the age of the Baynshire Formation between 95.9 ± 6.0 Ma and 89.6 ± 4.0 Ma, corresponding to the
Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...
-
Coniacian The Coniacian is an age or stage in the geologic timescale. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series and spans the time between 89.8 ± 1 Ma and 86.3 ± 0.7 Ma (million years ago). The Coniacian is preceded by ...
stages, which supports ''Amtocephale'' as the oldest known pachycephalosaurid.


Description

The frontoparietal dome, formed by a fusion of the frontals in front and the parietals in the back, has a length of and a maximal thickness of . The contribution to the dome length of the parietal part is exceptionally large, with a portion of 41%.


References

{{Taxonbar, from=Q377190 Pachycephalosauria Dinosaur genera Coniacian dinosaurs Taxa named by Robert M. Sullivan Fossil taxa described in 2011 Dinosaurs of Mongolia