Pachycephalosaurus

Reconstruction of Pachycephalosaurus

• USA

• P. wyomingensis ( Gilmore, 1931)

Pachycephalosaurus is a genus of bird Beck dinosaur ( Ornithischia ) from the group of Pachycephalosauria. He is the namesake and largest known representatives of this group of dinosaurs.

Features

So far only the skull of Pachycephalosaurus known. Was characteristic, as with all Pachycephalosauriern the strongly thickened skull roof, from the frontal bone ( frontal ) and the parietal ( parietal ) was formed. It was arched dome-like and up to 25 inches thick. Sides and back of the skull there were bony hump, and the nose had some on upwardly projecting hump-like outgrowths. The teeth were - if known - very small and had triangular, slightly jagged crowns on. Maybe had Pachycephalosaurus like other Pachycephalosaurier different tooth types.

The rest of the Body of this dinosaur is not known. Presumably he moved like the other Pachycephalosaurier biped continued ( on the extended hind legs ). Estimates of the total length amounts to between 5 to 8 meters.

Paleobiology

The construction of the teeth suggests a predominantly plant-based diet, possibly supplemented by insects. Most Discussed issue of Paleobiology of Pachycephalosaurus is probably the function of the thickened skull roof. Since the 1950s, the theory is popular, these are for ramming - been used, similar to today's bighorn sheep - about struggles over the mating privilege. Other opinions indicate these animals in effect implemented impacts on the flanks of the enemy or the eye-catching skull structures were used only for display or for identification. For details, see in function of the cranial vault in the Pachycephalosauria.

Discovery and designation

Fossil remains of Pachycephalosaurus were found in Wyoming, South Dakota and Montana in the United States. In addition to an almost complete skull and some isolated skull roofs are known. First, the findings in 1931 by Charles W. Gilmore were classified in the genus Troodon. It was only in 1943 recognized Barnum Brown and Erich Schlaikjer, that this was a new genus, for which they coined the name Pachycephalosaurus.

The name derives from the words pachys ( = " fat" ), kephale ( = " head") and saurus ( = " lizard" ) from. All finds are the Upper Cretaceous (late Maastrichtian ) dated millions of years ago, about 69 to 66, so that Pachycephalosaurus one of the youngest known dinosaurs.

System

Today, only one species is recognized in the genus Pachycephalosaurus with P. wyomingensis. Brown and Schlaikjer had two other species, P. and P. grangeri reinheimeri described. The genus Tylosteus in 1872 by Joseph Leidy described with reference to a shed leg is now regarded as a synonym of Pachycephalosaurus.

The systematic position within the Pachycephalosauria is not entirely clear. Traditionally, Pachycephalosaurus the group with a dome-shaped skull ( " Pachycephalosauridae " ) assigned, since the discovery of flat -headed, but possibly closely kindred with Pachycephalosaurus Dracorex this view has been shaken. In the opinion of R. Sullivan Pachycephalosaurus together with Dracorex and Stygimoloch a group of closely related dinosaurs that Pachycephalosaurini. John Horner and Mark Goodwin assume that Dracorex and Stygimoloch represent younger growth stages of Pachycephalosaurus and have an extreme change in skull shape during growth for the genus after.