Dinosaurs Protoceratops.
Aside from passing air along to the lungs, the function of these narial crests is not widely agreed upon. Sound production (honking), an improved sense of smell, or a visually conspicuous ornament for species recognition are some of the variously accepted suggestions. Since these animals are no longer considered to have been amphibious, ideas like snorkeling and extra air storage space have generally been discarded.
Pachycephalosauria
In important respects the pachycephalosaurs conformed to the basic ornithopod body plan (some experts include them with the Ornithopoda rather than as a separate infraorder). All appear to have been bipedal, possessed the typical ornithopod ossified tendons along the back, and had simple leaf-shaped teeth, although the teeth were enameled on both sides. The ornithischian type of pelvis was present, but the obturator process of the ischium was not. The pachycephalosaurs are known as domeheads, because of their most distinctive feature‹a marked thickening of the frontoparietal (forehead) bones of the skull (see illustration). The thickness of bone was much greater than might be expected in animals of their size. The suggestion has been made that this forehead swelling served as protection against the impact of head-butting activities such as those seen today in animals like bighorn sheep.
Stegoceras and Pachycephalosaurus of the North American Cretaceous were the smallest and largest members of the group, the former attaining a length of about 2.5 metres and the latter twice that. Pachycephalosaurs existed almost entirely in the Late Cretaceous (although Yaverlandia is from the Early Cretaceous) and have been found mostly in North America and Asia. The origin of the group is not known, but most likely it derived from some undiscovered Late Triassic or Early Jurassic hypsilophodont.
Ceratopsia
The first ceratopsian Dinosaur remains were found in the 1870s by E.D. Cope, who named the animal Agathaumus, but the material was so fragmentary that its unusual design was not at once recognized. The first inkling that there had been horned Dinosaur did not emerge until the late 1880s with the discovery of a large horn core, first mistaken for that of a bison. Shortly afterward, dozens of large skulls with horns were found‹the first of many specimens of Triceratops .
Ceratopsians were a relatively short-lived Dinosaur group, flourishing from the Middle Cretaceous to the ³great extinction² at the end of the Cretaceous Period. Triceratops, together with Tyrannosaurus, was one of the very last of all dinosaurs. Ceratopsians had a peculiar geographic distribution: the earliest and most primitive kinds, Psittacosaurus and Protoceratops, are known only from Asia‹Mongolia and China specifically; all the advanced ceratopsians, with the exception of a few fragmentary and doubtful specimens, have been found only in North America.
Sizes ranged from relatively small animals the size of a collie to the nine-metre-long, four- to five-ton
Triceratops. Although commonly compared to the modern rhinoceros, Triceratops grew to a weight and bulk
several times that of the largest living rhinoceros, and its behaviour probably was correspondingly different. The
most distinctive feature of nearly all members of the group was the horns on the head, giving them the name
ceratops (³horn face²). Correlated with the various arrays of head horns in the different taxa was the unusually
large size of ceratopsian heads. Great bony growths extended from the back of the skull, reaching well over the
neck and shoulders. This neck shield, or frill, resulted in the biggest head that ever adorned any land animal; the
length of the Torosaurus skull was almost three metres, longer than a whole adult Protoceratops.
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Alternative Theory On Dinosaurs
Paleontology
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