''Foraminacephale'' (meaning "

foramina In anatomy and osteology, a foramen (; : foramina, or foramens ; ) is an opening or enclosed gap within the dense connective tissue (bones and deep fasciae) of extant and extinct amniote animals, typically to allow passage of nerves, arter ...

head") 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 ...

pachycephalosaurid 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 ...

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

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 ...

(

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 ...

stage) deposits of

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

Description

''Foraminacephale'', as a pachycephalosaurid, was a small, bipedal herbivore with a thickened dome on its skull. In 2016,

Gregory S. Paul Gregory Scott Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology. He is best known for his work and research on theropoda, theropod dinosaurs and his detailed illustrations, both l ...

estimated its length at , its weight at . In ''Foraminacephale'', the top surface of the dome is punctuated by many small pits, the eponymous foramina; the dome itself consists of a large, central lobe with a sloped frontal half, and two smaller lateral lobes at the front. The

squamosal bone 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 ...

forms a tall bar of completely smooth bone underneath the dome, save for six bony nodes that line the bottom edge of the dome and an additional "corner" node just below. These features differentiate ''Foraminacephale'' from all other pachycephalosaurids. Unlike ''

Stegoceras ''Stegoceras'' is a genus of Pachycephalosauria, pachycephalosaurid (dome-headed) dinosaur that lived in what is now North America during the Late Cretaceous Period (geology), period, about 77.5 to 74 million years ago (mya). The first specim ...

'', ''

Hanssuesia ''Hanssuesia'' is a genus of pachycephalosaurid dinosaurs from the late Cretaceous period. It lived in what is now Alberta and Montana, and contains the single species ''Hanssuesia sternbergi''. ''Hanssuesia'' is based on a skull dome originall ...

'', and '' Colepiocephale'', the

parietal bone The parietal bones ( ) are two bones in the skull which, when joined at a fibrous joint known as a cranial suture, form the sides and roof of the neurocranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four bord ...

of ''Foraminacephale'' (which constitutes the back part of the dome) projects backwards and downwards over the base of the skull. Two traits also differentiate ''Foraminacephale'' from ''

Sphaerotholus ''Sphaerotholus'' is a genus of pachycephalosaurid dinosaur from the Upper Cretaceous of the western United States and Canada. To date, five species have been described: the type species, ''S. goodwini'', from the Den-na-zin Member of the Kirtla ...

'' and ''

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''. Discovery The holotype specime ...

'': there are prominent grooves between the central lobe and the lateral lobes, and the opening of the

temporal bone The temporal bone is a paired bone situated at the sides and base of the skull, lateral to the temporal lobe of the cerebral cortex. The temporal bones are overlaid by the sides of the head known as the temples where four of the cranial bone ...

is slit-like. Micro-CT scans of a potential specimen, identified as cf. ''Foraminacephale brevis'', support that pachycephalosaurids likely engaged in head-butting.

Ontogeny

As with ''Stegoceras'', the wide age range present in specimens of ''Foraminacephale'' allows for analysis of the ontogeny, or growth, of the dome. Measurements of 27 different points on 21 ''Foraminacephale'' skulls showed that the dome became proportionally taller with age, but did not become significantly wider.

Histology Histology, also known as microscopic anatomy or microanatomy, is the branch of biology that studies the microscopic anatomy of biological tissue (biology), tissues. Histology is the microscopic counterpart to gross anatomy, which looks at large ...

of the specimens showed that the domes became less porous with age - the smallest specimen's skull was 1.67% empty space, while the largest specimen's skull was 0.25% empty space. Generally, the frontal part of the dome was more porous than the parietal part. The growth series of the dome allows ''Foraminacephale'' to be differentiated further from ''Stegoceras''. In young ''Stegoceras'', the dome is flat; however, in even the smallest ''Foraminacephale'' specimens, the parietal is already slightly domed. The

supratemporal fenestrae Temporal fenestrae are openings in the Temple (anatomy), temporal region of the skull of some Amniote, amniotes, behind the Orbit (anatomy), orbit (eye socket). These openings have historically been used to track the evolution and affinities of re ...

on the top of the skulls of ''Foraminacephale'' are slit-like, as opposed to ''Stegoceras'' where they are round, and they seal shut very early in ontogeny as opposed to remaining open more-or-less throughout the animal's lifespan. The amount of empty space in the skull roof was also smaller relative to ''Stegoceras'', and more similar to ''

Acrotholus ''Acrotholus'' (Greek for "highest dome"- akros meaning highest and tholos meaning dome) is an extinct genus of pachycephalosaur dinosaur that lived during the Santonian of the late Cretaceous, in the Milk River Formation of Canada. The type spe ...

''. Furthermore, in ''Foraminacephale'', the squamosal and

postorbital The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some ve ...

bones became part of the dome much quicker, the dome thickened at a slower rate, and the sides of the dome were less angled than in ''Stegoceras''.

Discovery and naming

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 ...

of ''Foraminacephale'' is CMN 1423, a nearly complete frontoparietal dome collected in

Dinosaur Provincial Park Dinosaur Provincial Park is a UNESCO World Heritage Site situated 220 kilometres (137 mi) east of Calgary, Alberta, Canada; or northeast of Brooks. The park is situated in the Red Deer River valley, which is noted for its striking badland topo ...

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 ...

in 1902 and reported on during the same year. The layers of rock where the specimen were found belong to 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 7 ...

of the

Belly River Group The Belly River Group is a stratigraphic unit of Late Cretaceous age in the Western Canadian Sedimentary Basin. It takes the name from the Belly River, a tributary of the Oldman River in southern Alberta, and was first described in outcrop on t ...

. Various other fragments of the skull are also known from the Dinosaur Park Formation, representing juvenile, subadult, and adult individuals. Although it has been reported that many specimens are known from the contemporary

Oldman Formation The Oldman Formation is a stratigraphic unit of Late Cretaceous (Campanian stage) age that underlies much of southern Alberta, Canada. It consists primarily of sandstones that were deposited in fluvial channel and floodplain environments. It was ...

, only one (catalogued as TMP 2015.044.0041) can definitely be assigned to ''Foraminacephale''. Another specimen 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 th ...

formerly assigned to ''Foraminacephale'', CMN 11316, was re-identified as a small, juvenile indeterminate pachycephalosaurine. CMN 1423 was first assigned to a new species of ''

'' by

Lawrence Lambe Lawrence Morris Lambe (August 27, 1863 – March 12, 1919) was a Canadian geologist, palaeontologist, and ecologist from the Geological Survey of Canada (GSC). His published work, describing the diverse and plentiful dinosaur discoveries from t ...

in 1918; there was considerable debate over whether ''"S." brevis'' represented a truly distinct animal or simply a morph, perhaps the female, of ''S. validum''. Later, it was assigned to ''

'' by Robert M. Sullivan in 2000, and then it was assigned to ''

'' by Longrich, Sankey & Tanke in 2010. In 2011, Ryan Schott suggested a new generic name, ''Foraminacephale'', in his

Master of Science A Master of Science (; abbreviated MS, M.S., MSc, M.Sc., SM, S.M., ScM or Sc.M.) is a master's degree. In contrast to the Master of Arts degree, the Master of Science degree is typically granted for studies in sciences, engineering and medici ...

thesis, resulting in a new combination ''Foraminacephale brevis''. It remained an invalid ''nomen ex dissertatione'' until Schott and David Evans formally renamed ''"S." brevis'' to ''Foraminacephale brevis'' in 2016. The generic name combines Latin ''foramina'' ("foramina") with ''cephale'', Latinised Greek for "head", referring to the many pits that covered the top of its dome.

Classification

A phylogenetic analysis in 2016 found that ''Foraminacephale'' was a member of the Pachycephalosaurinae, in a more derived position than ''

'', but in a more basal position than ''

''. The consensus of the phylogenetic trees recovered is shown below. The topology of this phylogenetic tree is not very stable, likely due to the incompleteness of most pachycephalosaur specimens.

Paleoecology

The

is particularly rich in pachycephalosaur remains; 70% of all known pachycephalosaur fossils come from this region. Because of a lack of understanding of pachycephalosaur ontogeny, various authors have assigned this material to anywhere from a single species, ''

Stegoceras validum ''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 descr ...

'', to four different genera. This has significant implications for the Late Cretaceous biodiversity of herbivorous dinosaurs. The 2016 description of ''Foraminacephale'' recognized four distinct species of pachycephalosaur from the Belly River Group: ''Stegoceras'', ''Foraminacephale'', ''

'', and '' Colepiocephale'', although the specimens that have been referred to ''Hanssuesia'' likely represent more than one of the existing species.

References