Dinosaurs Theories.
Here we see a model taking shape.
Several theories have been proposed to explain this frill structure: a protective shield to cover the neck region, an attachment site of greatly enlarged jaw muscles, an attachment site of powerful neck muscles for wielding the head horns, or a sort of ornament to present a huge, frightening head-on profile to potential attackers. Most probably, all these functions were involved at some stage in the development of the frill. The most unusual thought is that the structure was none of these, but rather acted as a giant heat-control apparatus, with its entire upper surface covered in a vast network of blood vessels pulsing with overheated blood or absorbing solar heat. The idea is interesting but fails to account for several important associated features -the massive coronoid process of the lower jaw, for example - that are better explained as mechanical and muscular adaptations.
The infraorder is usually divided into three families: the primitive psittacosaurids, including the putative ceratopsian ancestor, Psittacosaurus; the protoceratopsids, including Protoceratops of Asia and Leptoceratops of North America; and the ceratopsids, encompassing all the advanced and better-known kinds such as Triceratops, Torosaurus, and Monoclonius, all from North America.
Psittacosaurus has sometimes been classified as an ornithopod, largely because of its relatively long hind limbs and short front limbs, probably resulting in bipedal stance and locomotion. Resembling ornithopods in body form, it had a shorter neck and tail and was much smaller (only two metres long) than the most advanced ornithopods like the iguanodonts and hadrosaurs. Psittacosaurus, however, possessed a ceratopsian-like beak, the beginnings of a characteristic neck frill at the back of the skull, and teeth that prefigured those of the more advanced ceratopsians. Also, its remains have been found in rocks that predate those containing the ceratopsids.
The best-known of the protoceratopsids is the genus Protoceratops. Dozens of skeletal specimens have been found and studied, ranging from near hatchlings to full-size adults. This rare treasure, the first to include very young individuals unmistakably associated with mature individuals, was the result of the series of American Museum of Natural History expeditions in the 1920s to the Gobi. Their collection provided the first good growth series of any dinosaur. Even more momentous was their discovery of several nests of eggs loosely associated with Protoceratops skeletons‹the first certifiable Dinosaur eggs. Additional specimens of Protoceratops and its nests of eggs were recovered on subsequent expeditions by Soviets, Poles, and Chinese.
The skeletal anatomy of the protoceratopsids foreshadowed that of the more advanced ceratopsids. The ceratopsian skull was disproportionately large for the rest of the animal, comprising about one-fifth of the total body length in Protoceratops and at least one-third in Torosaurus . The head frill of Protoceratops was a modest backward extension of the upper temporal fenestral arches but became the enormous fan-shaped ornament of later forms. Protoceratops also displayed a short but stout horn on the snout, a development of the nasal bones; this too was a precursor of the prominent nasal horns of ceratopsids like Monoclonius , Centrosaurus, Chasmosaurus, Styracosaurus, Torosaurus, and Triceratops. The last two genera developed two additional, larger horns above the eyes. These horns undoubtedly were covered by horny sheaths or soft tissue, as is evidenced by impressions on them of superficial vascular channels for the nourishing blood vessels.
Ceratopsian jaws were highly specialized. The lower jaw was massive and solid to support a large battery of teeth similar to those of the duckbills. The front of the lower jawbones met in a long, strong symphysis capped by a stout beak formed of the toothless predentary. This structure itself must have been covered by a sharp, horny, turtlelike beak. Continuous dental surfaces extended over the rear two-thirds of the jaw. The tooth batteries, however, differed from those of the hadrosaurs in forming long, vertical slicing surfaces as upper and lower batteries met, operating much like self-sharpening shears.
From the lower jaw a massive coronoid process jutted up toward a relatively small upper temporal fenestra, providing a strong attachment point for jaw muscles and powerful leverage for their action. Because the upper fenestra was so small, and the teeth so specialized for cutting, it has generally been accepted that the powerful jaw muscles were attached to the upper frill surface and connected to the coronoid process beneath by means of a stout tendon passing through the upper fenestra. At least one factor in the expansion of the skull frill would seem to have been the size of the required jaw muscles. (That, however, would not have precluded other functions for the frill as well‹shielding the neck, enlarging the head-on profile, or even controlling temperature.)
As in the hadrosaurs, each dental battery consisted of about two dozen or more tooth positions compressed
together into a single large block of teeth. At each tooth position there was one functional, or occluding, tooth
(the duckbills had two or three) along with several more unerupted replacement teeth beneath. (All toothed
reptiles, living and extinct, have a lifelong supply of replacement teeth.) An intriguing question arises: what did
the ceratopsians feed on that required such an unusual and powerful feeding mechanism? The answer remains
hidden, but the suggestion is that they fed on something exceedingly tough and fibrous, like the fronds of palms
or cycads, both of which were plentiful during late Mesozoic times.
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Original Source - http://www.crystalinks.com/
Alternative Theory On Dinosaurs
Paleontology
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