Ornithischia

Hip joint of Edmontosaurus, an hadrosaurider ornithischians

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The bird Beck dinosaur ( Ornithischia ) in addition to the lizards Beck dinosaurs ( Saurischia ) one of the two orders of dinosaurs.

This differentiation of the dinosaur was a large step towards a better understanding of their relationships and was in 1887 by Harry Govier Seeley from King's College London. Until then, quite a few well-preserved dinosaur skeletons had been described and Seeley noticed that one could classify them based on their pelvic anatomy in two groups. Seeley called these two groups Saurischia and Ornithischia.

Features

The arrangement of the pelvic bones of bird Beck dinosaurs resembles that of the birds, which Seeley led to the choice of this name. However, the birds are dinosaurs lizards Beck, the anatomical similarity is only superficial. While ischium ( ischium ) and ilium ( ilium ) are arranged in the orientation as in the lizards Beck dinosaurs, the pubic bone ( pubis ) is not down and slightly forward to the head, but consists of a narrow, rod-shaped bone, which along ischium next to the lies and pointing backwards. Ilium, ischium and pubis to form a twin structure in the Saurischiern the basin, however, is three units. In some bird Beck dinosaurs - especially for those from the Upper Cretaceous as the Ceratopsia or Ankylosauria - differs from the basin of this structure. The pubic bone is reduced and forms a new, forward-facing spinous process, the Präpubis; the basic structure is still recognizable.

The cause of the backward "rotated " pubis is unclear, as fossil evidence for the early stages of development are lacking. One explanation alone of the bipedal lifestyle ago contradicts that this feature is absent in similar living Saurischia as Coelophysis and on the other hand, for example in the Hypsilophodontidae, which are among the Ornithischia, by developing a distinctive Präpubis - extension forward an approximation to the Saurischia - pelvic structure was. It is possible that the need for forward movement of the thigh muscles anlagerten to other bones instead of the pubis, so that it could be re-formed or is set back to give the thighs more freedom of movement and more space for the plant to digest food important intestinal tract to create. Another reason may be the more favorable position of the center of gravity for this often bipedal ( two-legged ) dinosaurs been his ..

Apart from the different pelvic bone, this group also includes other characteristics that are not found in the lizards Beck dinosaurs. All bird Beck dinosaur wore on the tip of the lower jaw bone, the Praedentale. Somewhat less striking are the rows extended spinous processes, which probably helped streamline and support the back. Unlike lizards Beck Beck dinosaur dinosaur bird were herbivores with a significantly greater species richness.

System

The following cladogram makes the family relationships of the main groups of Ornithischia clear:

Pisanosaurus

Heterodontosauridae

Stegosauria

Ankylosauria

Stormbergia

Hexinlusaurus

Agilisaurus

Ornithopods

Pachycephalosauria

Ceratopia

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