COHOST DINOOLVEIA: Order Saurischia. Primitively carnivorous dinosaurs.
Suborder Theropoda. Bipedal carnivorous dinosaurs. Suborder Sauropoda. Quadrupedal, amphibious, plant feeding dinosaurs.
Order OrnitAischia. Predentate or beaked herbivorous dinosaurs.
Suborder Ornithopoda. Bipedal unarmored dinosaurs. Suborder Stegosaur's. armored dinosaurs. Suborder Ceratopsia. QQuadrupedal horned dinosaurs.
The two main phyla or orders of dinosaurs have received the rather cumbrous names of Saurischia (Gr. aaput, lizard, and 'roxtor, hip joint) and Omithischia (Gr. opvic, bird), be cause of the basic structure of their pelvis, which in the one case resembles that of the crocodile or saurian and in the other that of the bird, and, as has been said, there is evidence that the relationship thus implied is real. In many ways the two groups give evidence of having undergone closely parallel lines of evolu tionary progress, especially in their method of locomotion and consequently in their motor organs. This is particularly true of the first suborder in each phylum, the Theropoda and Omithopoda. Out of each of these more con servative stocks arose aberrant lines in which a premium was placed either on bulk (Sauro poda) or on armor (Stegosauria) or on wea pons (Ceratopsia), with consequent modifica tions and specializations far removed from the primitive stock. Then, too, there was on the part of the two main orders the diametrically opposed dietary — flesh on -the one hand, with its relatively simple dental and digestive mechan ism, and vegetal food on the other, with a re sultant complexity of dentition in the more highly specialized members which has never been surpassed.
Sanriachia — Theropoda. The earliest known dinosaurs belong to the Saurischia, suborder Theropoda, and they existed with but little change until the close of the Mesozoic. They were bipedal, with four-toed, bird-like feet, armed with increasingly powerful claws, and with four-fingered hands provided with grasp ing talons. The skull was lightly constructed,
somewhat bird-like in form, but possessing no beak. On the contrary, their powerful jaws were armed with a single row of teeth, often flattened, curved and dagger-like, with finely serrate margins which must have made them highly efficient for tearing and rending their prey, but not for mastication. The teeth were mainly in the forward portion of the jaws. The head was poised at right angles to the rather short neck and the compact trunk was followed by a long and often very slender tail which served to counterbalance the weight of the body and head when they were borne on the hind limbs in a semi-erect posture. From an. ex haustive study of dinosaurian footprints which exist by the thousands impressed upon the Triassic rocks of the Connecticut Valley, one is justified in assuming that the fore feet were never brought into contact with the ground, al though they doubtless were of use in fighting or in grasping the prey. There is as yet no direct evidence of the nature of their skin ex cept on the sole of the foot, but we have no reason to suppose that it was other than reptile like, clothed in all probability with a flexible scaly covering, but otherwise unarmored.
The Theropoda were highly conservative, in creasing in general dimensions and consequent prowess, with the peculiar exception that in the larger forms, the megalosaurs, the hands failed to keep pace with the general increase in stature until in the final forms they were rela fixely so absurdly small that it is difficult to conjecture their use. But not all Theropoda were of this sort, for another group remained relatively small, agile forms until the end of their racial career. At least one of these (Struthiomimus) became entirely toothless — a sign of degeneracy, but in this instance coupled with an otherwise efficient body, which makes the interpretation of habits and habitat a matter of great doubt.