Having looked at how to relate and name animals, it is time to start a predatory dinosaur cladogram. (walking dinosaur costume) The very primitive diapsid reptiles are chosen as the outgroup. Generally, diapsids have two temporal openings in the skull behind the orbit, or eye socket (realistic dinosaur costume); other reptiles have only the upper one of these, or neither. Lizards, crocodilians, and birds are living diapsids. A key feature further uniting some diapsids is yet another opening in front of the orbit. Diapsids with this preorbital opening are classified as archosaurs, among which are birds and crocodilians. Actually, living birds and crocodilians have little or no preorbital opening left, but their earliest forms did. Lizards and their ancestors never had apreorbital opening and are not archosaurs.
Among extinct animals, thecodonts, pterosaurs, and dinosaurs had a preorbital opening, and with crocs and birds form the Archosauria. Most of these also share more erect gaits, and a bird-type bone histology that, (Animatronic dinosaur), suggests they had faster growth rates and heightened metabolisms. The higher level systematics of these archosaurs, and the dinosaurs they include, is in a great state of flux. The traditional way of classiSring dinosaurs is no longer preeminent and in fact is so obsolete that it is misleading to perpetuate it. For this reason, in this book I have gone ahead and offered a new reorganization of predatory dinosaur taxonomy and systematics, even though the phylogenetic conclusions it is based upon are not yet firm. I do so because some working scheme is needed, and because I doubt that the phylogenetics will solidif,i soon enough to produce a better anangement before this book is published. Dinosaurs have traditionally been classified as two separate orders of the subclass Archosauria, in the class Reptilia. But dinosaurs are radically different from all living reptiles. As we have seen, structurally and physiologically they are more like birds. It makes no more sense to put TJnannoscurus and Tbfceratops in the sarne group as turtles andlizards than it does to put birds in the Reptilia. Starting with Robert Bakker and Peter Galton in 1974, this has led a number of scholars to suggest that dinosaurs and birds be united in a class of their owrr, Probably it is best simply to raise the Archosauria to class rank, and include in it thecodonts, crocodilians, pterosaurs, dinosaurs, and birds. Some have criticized the use of the archosaur’s high growth and metabolic rates to define this group. But the classes Aves and Mammalia have long been defined, in part, by their warmblooded nature. Besides, the archosaur’s distinctive bone histology is itself a hard, morphological character that can be directly measured. The whole idea of taking crocodilians and dinosaurs out of reptiles and putting them together with birds has met considerable resistance. But if archosaurs are given a new class, then there is no justification for keeping their very similar avian descendants in another class. Whatever happens, at least dinosaurs and their relatives are no longer either “lower” vertebrates or reptiles, they are archosaurs, equal to mammals in status.