Pachycephalosaurus (thick headed lizard)
Pachycephalosaurus (thick headed lizard)
Named By : Barnum Brown & Erich Maren Schlaikjer - 1943
Diet : Herbivore / Omnivore
Size : Estimated 8 meters long
Type of Dinosaur : Euornithopod
Type Species : P. wyomingensis (type)
Found in : USA
When it Lived : Late Cretaceous, 76-65 million years ago
Pachycephalosaurus (/,paekI,sef@l@’so:r@s/; meaning “thick-headed lizard”, from Greek pachys-/pakhus- “thick”, kephale/kephale “head” and sauros/sauros “lizard”) is a genus of pachycephalosaurid dinosaurs. P. wyomingensis is the type species. It lived in what is now North America’s Late Cretaceous Period (Maastrichtian phase). There have been remains found in Montana, South Dakota and Wyoming. It was a herbivorous creature that is only known from one skull and a few very thick skull roofs. The skull roofs were 9 inches thick. Recent years have seen more complete fossils. Pachycephalosaurus was one of the last non-avian dinosaurs to survive the Cretaceous–Paleogene extinction. Tylosteus, a western North American dinosaur, has been compared to Pachycephalosaurus. Recent studies also have identified the genera Stygimoloch, Dracorex, and Dracorex.
Pachycephalosaurus, like other pachycephalosaurids was a bipedal herbivore. It had a thick skull roof. It had long hindlimbs, and small forelimbs. Pachycephalosaurus, the largest pachycephalosaur known, is Pachycephalosaurus. Pachycephalosaurus’s skull domes, and those of related genera, led to the idea that pachycephalosaurs may have used their skulls for intra-species fighting. In recent years, this hypothesis has been challenged.
Pachycephalosaurus remains may have been discovered as early as 1850. Donald Baird has determined that Ferdinand Vandeveer Hayden (1859-1868), an early collector of fossils in the North American West, found a bone fragment near the Missouri River’s head in what is now the Lance Formation in southeast Montana. Joseph Leidy described this specimen (ANSP 8568) in 1872 as belonging the dermal armor of a reptile, or an armadillo like animal. Tylosteus was given its name. Baird, who restudied the specimen over a century later, discovered its true nature and identified it as a Pachycephalosaurus squamosal (bone at the back of skull). He also found a set bony knobs that resemble those on other Pachycephalosaurus specimens. According to the International Code of Zoological Nomenclature, Tylosteus is preferred because it predates Pachycephalosaurus. Baird petitioned for Pachycephalosaurus to be used in 1985. The latter name was not used for more than fifty years and was based on poor stratigraphic and geographic information. However, this may not be the end. Robert Sullivan suggested that ANSP 8568 was more similar to the corresponding bone from Dracorex than the one of Pachycephalosaurus in 2006. However, it is not clear if Dracorex represents a juvenile Pachycephalosaurus as was recently suggested.
Charles W. Gilmore named P. wyomingensis in 1931, as the only valid type of Pachycephalosaurus. It was named for the partial skull USNM 12311, which is located in the Lance Formation, Niobrara County. Gilmore assigned Troodon to T. wyomingensis, his new species. Paleontologists believed that Troodon was the same species as Stegoceras at the time. They had similar teeth. The family Troodontidae was assigned what we now call pachycephalosaurids, a mistake that Charles M. Sternberg corrected in 1945.
With newer and more complete material in 1943, Barnum Brown, Erich Maren Schlaikjer established the genus Pachycephalosaurus. Two species were named: Pachycephalosaurus Reinheimeri and Pachycephalosaurus Grangeri. P. grangeri was based upon AMNH 1696. This skull is from the Hell Creek Formation in Ekalaka, Carter County. Montana. P. reinheimeri was based upon what is now DMNS469, a dome with a few elements from the Lance Formation in Corson County, South Dakota. They also refer to the older species Troodon wyomingensis as their new genus. Since 1983, their two more recent species were considered synonymous with P. Wyomingensis.
Pachycephalosaurus was discovered in Scollard Formation (Alberta, Canada) in 2015. This suggests that dinosaurs from this era were multi-ethnic and did not have distinct faunal provinces.