Alaskacephale

Extinct genus of dinosaurs

Alaskacephale is an extinct genus of pachycephalosaurid, a group of dome headed, herbivorous ornithischian dinosaurs, that lived during the Campanian stage of the Late Cretaceous period in what is now northern Alaska. The genus is one of the few known Arctic dinosaurs and was found in the Prince Creek Formation, which preserves a menagerie of fossils. The only known specimen, a squamosal bone, was found in 1999 and later described in 2005. However, Alaskacephale was not formally named until the next year. Alaskacephale, due to the lack of fossil remains, is poorly known. Despite this, the presence of bony protuberances from the skull prove that it was a pachycephalosaur. Later phylogenetic analyses suggest it was a close relative of Pachycephalosaurus. However, Alaskacephale is distinguished from other genera by the two rows of nodules found along the squamosal. The Prince Creek Formation bears a variety of fossils, many of them similar to other previously known Laramidian taxa. Alaskacephale coexisted with dinosaurs like the ceratopsian Pachyrhinosaurus, ornithopod Edmontosaurus, and tyrannosaurid Nanuqsaurus in addition to mammals like Unnuakomys.

In 1999 during an expedition by the University of Alaska, an isolated pachycephalosaur squamosal was unearthed from bluffs on the bank of the Colville River in North Slope Borough, Alaska. Strata (rock layers) deriving from this area come from the latest Campanian aged (72 71 mya) Prince Creek Formation. The fossil was then deposited in the University of Alaska Museum and described in 2005 by Roland Gangloff and colleagues as belonging to a pachycephalosaurine closely related to, and possibly, Pachycephalosaurus.

The dimensions of the holotype suggest that A. gangloffi was about half the size of Pachycephalosaurus wyomingensis or three quarters the size of Prenocephale, and about the same size as Sphaerotholus and Foraminacephale. This would make Alaskacephale one of the smaller known pachycephalosaurs. The last pachycephalosaurs went extinct during the Cretaceous Paleogene extinction event, the last surviving genus being Pachycephalosaurus itself. However, a 2020 cladistic analysis recovered the heterodontosaurids as an early branch of the group, which extend the age of pachycephalosaurs as far back as the Early Jurassic. Currently, pachycephalosaurs are recognized as being part of the larger group Marginocephalia which encompasses it and the gigantic, horned ceratopsians. Within Pachycephalosaurinae, Alaskacephale belongs to the tribe Pachycephalosaurini, which contains Alaskacephale, Pachycephalosaurus, and, according to some phylogenetic analyses, Stygimoloch, Dracorex, and Sphaerotholus. Pachycephalosauria originated in Asia but later colonized North America. The Asian members of this clade are more basal compared to the North American genera, which bear more derived characteristics. Pachycephalosaurini is the most advanced group in Pachycephalosauria and is made up of North American members. Below is a cladogram from Evans et al., 2021.

Alaskacephale lived alongside many other dinosaurs during latest interval of the Campanian stage. Having resided at an estimated 80°–85°N paleolatitude, the area Alaskacephale thrived in experienced climatic extremes unlike that experienced by most other dinosaurs. The temperature of this Northern environment would've ranged from around 10 to 12 °C during the warmer months and about 2 °C ± 3.9 °C during the colder months. As well as this, the environment would have faced 120 days of continuous low light conditions during the Winter. In contrast to the contemporary large herbivores Edmontosaurus and Pachyrhinosaurus, which preferred coastal lowland and upland environments respectively, Nanuqsaurus appears to have been fairly ubiquitous throughout the Prince Creek landscape. an unnamed lambeosaurine, an unnamed thescelosaurine (mentioned to be similar to Parkosaurus and Thescelosaurus), an unnamed orodromine (mentioned to be similar to Orodromeus), the ceratopsid Pachyrhinosaurus perotorum, the tyrannosaurid Nanuqsaurus, a large troodontid referred to the dubious genus Troodon, the dromaeosaurid Dromaeosaurus, the dromaeosaurid Richardoestesia (similar to R. isosceles), an unnamed saurornitholestine, an unnamed ornithomimosaur, and multiple avialans. As well as this, several mammals, including the metatherian Unnuakomys, the eutherian Gypsonictops, both an unnamed and named multituberculate, the latter being Cimolodon, and finally an indeterminate marsupial. Interestingly, due to the cooler conditions of this habitat, many otherwise common ectothermic clades lack representation entirely in the Prince Creek Formation, suggesting that all the animals that did thrive in these extreme latitudes were indeed endotherms to some degree.