Having looked at paleodinosaurs and heneravians

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Having looked at paleodinosaurs and heneravians, we now turn to the biggest predatory dinosaur superorder, Theropoda. (walking dinosaur costume)As the theropods evolved, they tended to become increasingly birdtike. But this is a large and complex group that exhibited much parallelism, some important reversals, and specializations of its own. It has become clear that the old way of dividing theropods into two simple groups is useless. In the old arrangement, the Coelurosauria hetd the small, hollow-boned species, starting with Triassic, kink-snouted Coelophysfs and ending with the Late Cretaceous ostrich-mimics, and the Carnosauria incorporated the big-bodied, big-headed, heavy-boned forms. This started with Dilophosaut’us, which also had a kinked snout, andMego’ loscurus, both of the Jurassic, and finished up in the Cretaceous with tyrannosaurs. This division was meaningless, for large size and stoutness of build and bones is just the sort of thing that many gloups tend to develop on their own. In 1984, Jacques Gauthier and Kevin Padian tried to revive and revise these old terms to fit the new phylogenetics, but the process of adapting them involves so much distortion that there is little point in doing so. At best, carnosaur and coelurosaur are informal terms for big and small theropods; it is better just to say big and small. A modern assessment of theropods finds that Theropoda contain two orders: the archaic Paleotheropoda and the more ad.vanced., more birdlike Avetheropoda, which includes the direct ancestors of birds. The two theropod orders are especially satis$ring because they each show about the same anatomical diversity as is found in the two ungulate orders, the perissodactlya (odd-toed horses and rhinos) and Artiodactyla (even-toed pigs, deer, and cattle), and both are marked by differing ankle and foot details (Animatronic dinosaur).

 

The most primitive paleotheropod is small procompsognafhus, which retains an archaic broad pubis. The least advanced of the namow-hipped theropods are the coelophysids. These include small coelophysians as well as larger dilophosaurs. (animatronic dinosaur for sale)Coelophysids are an example of a bewildering combination of primitive and derived characters. Quite primitive in most regards, dilophosaurs had only four hip vertebrae. Yet the group’s unique kinked articulation between the premaxillary and maxilla bones in the snout, the many co-ossified bones, and the unique double head crests, are advanced. Dilophosaurs were even more like advanced theropods in some other ways, and had a unique and sophisticated suspensorium (the complex of cheek bones that support the lower ju*). All this can be sorted out satisfactorily. The kinked snouts, crests, and peculiar jaw supports show that coelophysids were an increasingly aberrant side branch that left no descendants. This means they paralleled other advanced theropods and birds in such details as extensive bone ossification and increasingly narrow cannon bones (realistic dinosaur costume). crests, peculiar jaw supports, and narrow cannon bones show that dilophosaurs are the most advanced of the bunch, so their reduced hips must be a secondary reversal to a more primitive condition. It may be that the extraordinarily aberrant Boryonyr and Spinoscurus are extremely specialized developments of the dilophosaur branch; their deeply kinked snout and other similarities certainly suggest so.