Pachycephalosaurus
| Pachycephalosaurus | ||||||||||||
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Reconstruction of Pachycephalosaurus |
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| Temporal occurrence | ||||||||||||
| Upper Cretaceous (late Maastrichtian ) | ||||||||||||
| 69.9 to 66 million years | ||||||||||||
| Locations | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Pachycephalosaurus | ||||||||||||
| Brown & Schlaikjer, 1943 | ||||||||||||
| Art | ||||||||||||
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Pachycephalosaurus is a genus of pelvic dinosaurs (Ornithischia) from the group of Pachycephalosauria . He is the namesake and largest known representative of this group of dinosaurs.
features
So far, only the skull of Pachycephalosaurus is known. As with all pachycephalosaurs, the strongly thickened skull roof, which was formed from the frontal bone and the parietal bone, was characteristic. It was arched like a dome and up to 25 centimeters thick. On the side and back of the skull there were bony cusps, and the nasal bone also had some protruding cusp- like outgrowths. The teeth were - as far as known - very small and had triangular, slightly serrated crowns. Perhaps possessed Pachycephalosaurus like other Pachycephalosaurier different types of teeth.
The rest of the body structure of this dinosaur is unknown. Presumably he moved like the other Pachycephalosaurier biped (on the elongated hind legs). Gregory S. Paul estimated it in 2010 at 4.5 meters in length and 450 kilograms.
Paleobiology
The structure of the teeth suggests a predominantly plant-based diet, possibly supplemented by insects. The most discussed question of pachycephalosaurus palaeobiology is probably the function of the thickened skull roof. Since the 1950s, the thesis has been popular that these were used for ramming - for example in battles for the mating privilege - similar to today's bighorn sheep . Other opinions say that these animals used it to hit the opponent's flanks or that the conspicuous skull structures were only used for display or identification. For more information, see the function of the skull roof in the Pachycephalosauria .
Discovery and naming
Pachycephalosaurus fossil remains have been found in Wyoming , South Dakota, and Montana in the United States . In addition to an almost complete skull, some isolated skull roofs are also known. Initially, the finds were classified in 1931 by Charles W. Gilmore in the genus Troodon . It was not until 1943 that Barnum Brown and Erich Schlaikjer recognized that this was a new genus, for which they coined the name Pachycephalosaurus .
The name is derived from the words pachys (= "thick"), kephale (= "head") and saurus (= "lizard"). All finds are dated to the Upper Cretaceous (late Maastrichtian ) about 69 to 66 million years ago, making Pachycephalosaurus one of the youngest known dinosaurs.
Systematics
E u. F: fragmentary skull of Stygimoloch
G u. H: Dracorex skull , the youngest stage.
Today, with P. wyomingensis, only one species in the genus Pachycephalosaurus is recognized. Brown and Schlaikjer had described two other species, P. grangeri and P. reinheimeri . The genus Tylosteus , already described by Joseph Leidy in 1872 on the basis of a scaly leg, is now a synonym for Pachycephalosaurus .
The systematic position within the Pachycephalosauria has not been fully clarified. Traditionally, Pachycephalosaurus assigned to the group with a dome-shaped skull ( "Pachycephalosauridae"), since the discovery of the flat-headed, but may closely with Pachycephalosaurus kindred dracorex this view has been shaken. According to R. Sullivan, Pachycephalosaurus, together with Dracorex and Stygimoloch, form a group of closely related dinosaurs, the Pachycephalosaurini. John Horner and Mark Goodwin assume that Dracorex and Stygimoloch represent younger growth stages of Pachycephalosaurus and show for the genus an extreme change in the shape of the skull in the course of growth.
literature
- Teresa Maryańska , Ralph E. Chapman, David B. Weishampel : Pachycephalosauria. In: David B. Weishampel, Peter Dodson , Halszka Osmólska (eds.): The Dinosauria . 2nd edition. University of California Press, Berkeley CA et al. 2004, ISBN 0-520-24209-2 , pp. 464-477.
Individual evidence
- ^ Gregory S. Paul : The Princeton Field Guide To Dinosaurs. Princeton University Press, Princeton NJ et al. 2010, ISBN 978-0-691-13720-9 , p. 244, online .
- ^ Robert M. Sullivan: A taxonomic review of the Pachycephalosauridae (Dinosauria: Ornithischia). In: Spencer G. Lucas, Robert M. Sullivan (Eds.): Late Cretaceous Vertebrates from the Western Interior (= New Mexico Museum of Natural History and Science. Bulletin. 35, ISSN 1524-4156 ). New Mexico Museum of Natural History and Science, Albuquerque NM 2006, pp. 347–365, digital version (PDF; 4.79 MB) .
- ^ John R. Horner , Mark B. Goodwin: Extreme Cranial Ontogeny in the Upper Cretaceous Dinosaur Pachycephalosaurus. In: PLoS ONE . Vol. 4, No. 10, 2009, e7626, doi : 10.1371 / journal.pone.0007626 .
