DI'NOSAT.YRIA Nett-Lat., from Gk, cletpor, deinos, terrible -r st it rus. lizard,. An ordk r of fossil reptiles, found only in rocks of AleskLoic age, and containing some of the most wonderful and bizarre land animals that have over lived. In general, the dinosaurs present the same reptilian characters as do the and ptene.aarians, which have been de rived from the same original stuck, and within the order the form is 60 variable that it is difficult to tint reliable distinctive The more primitive genera can sea rmly be distinguished from the general ized eroc.,dilcs, others semble the rhynchocephalians, others the ptero saurian:, and still others are f: r Tt Moved by specialization alon• par ticular lines and afford most re markable and extravagant forms. The closest living allies of the dino saurs are the eroeodiles and the ratite birds (ostrich, utc.1, which, with the more primitive dinosaurs, were probably descended from a eonniu n ancestral stock in early Triassic times.
The skeleton of dinosaurs pre sents some variations from that of other reptiles. The cranium has two temporal vacuities. the v•rtebrw are double concave, though several anterior vertebrab in the more primitive genera may he con cave on the posterior surface only: the sacrum is usually of three or fused Vertebra., but the normal reptilian allmber, two, is found in I he primitive forms. The pelvis is of bird-like structure. often With anterior and posterior elongation of the elements. The limbs are fitted for loeomot ion on land : the forward pair is often reduced in size so that locomotion is bi pedal. Reduction of the number of toes on the hind feet to three is eonnnon. In some gigantic genera the tail was unusually strong and will' the hind limbs formed a tripod support for the animal, 'licit was thus imabled to raise its head to a hei!,lit sometimes of thirty feet above the ground. and to overlook the of the marshes in uhieh it \ allowed. The of dinosaurs is fitted for both earniv.)rous and herhivonms food. Deak-like structure of the jaws is com mon. Th, teeth are often implanted in sockets and in some they appear ill ,mereAsio11111 series. The bead of dinosaurs is usually di-pro portionately small• and the brain is always of very small size and low degree of eonvoltition, indicating an inferior grade of intellirn•nee in these animals, In some forms with small head. )(mg neck, heavy body and hind quarters, and long heavy tail, where the hinder part of the body overbalances by far the forward portion, as in Brontosaurus, Diplodocus, Scelidosaurus, and Stegosaurus. the neural ganglion in the sacrum is many times larger than the cephalic ganglion or brain, a condition necessitated by the great mass of the body that must be innervated from the sacral ganglion in these animals.
In habits the dino saurs were terrestrial, and often amphibious, and the structure of the tail in some era indicates its use as a swimming organ. Some were of ful, bird-like action, walking, running, or leaping on their toed bind limbs. ers were heavy, clumsy beasts, walking or crawling on their idly built four legs. Dinosaurs vary ly in size. The est are of the size of a chicken. The largest are the greatest land animals ever known to have existed. with lengths of CO to 70 feet, heights of 10 to 20 feet. and weights estimated to have varied from 20 to 25 tons. Dinosaurs appeared in the early Triassic time, and during the sic and Cretaceous periods they ruled the land, but toward the end of the Cretaceous they began to decline, and they filially gave way to the early mammals. The remains of the latest members of the order are found in the uppermost tions of the Cretaceous, namely the Laramie group of western America. Their remains have been found in the Mesozoic rocks; of Europe, southern Asia. South Africa, North Autralia. North and South America, and the most noted loealities whence they have been obtained are those of Bernissart in Belgium, and the Rocky Mountain reolon of North Anieriea. The order Dinosauria is divided into three suborder:. some of the peculiarities of which are here given. They are the Sauropoda. Theropoda, and Predentata. R.%1'HOPODA. This is the most primitive group of dinosaurs, resembling the eroeodile: and rhyn chocephalians in the structure of its skeleton and the proportions of its parts. IL includes the gigantic herbivorous genera: Atlantosaurns, Cetiosaurus, Brontosaurus (q.v.), and Dipiodo cus N\ ith very small head, long neck, heavy trunk supported on strong plaMi;_rade five-toed fore and hind limbs of equal size. and with a heavy long tail. The teeth are lolg, spatulate, and spreading. The bones are solid and heavy, and the pubis is simple. This group is mostly of Triassic and Jurassic age.
TnEnoroDA. Carnivorous dinosaurs with cut ting teeth in sockets. Their skeletons are of rather delicate construction and their vertebra; and limb-bones are hollow. Their live-toed fore limbs are of small size and apparently of little use as locomotory organs, but their three-toed hind limbs are strong and the toes are furnished with prehensile claws. These dinosaurs were digitigrade and they walked as do birds or leaped as do the kangaroos. The pelvic bones aro elon gated. Examples of this suborder are Anchi saurus and Ceratosaurus (qq.v.). Hallopus, a leaping dinosaur from the Jurassic of Colorado, and the bird-like Compsognathus, one of the smallest dinosaurs, from the Jurassic litho graphic limestones of Solenholen, Bavaria, also belong in this division.