The collective term “dinosaurs” (meaning terrible lizards) has been
given to that distinctive group of reptiles prominent in Mesozoic life
for some 140 million years. In size, the dinosaurs ranged from as little
as 1 foot to as much as 85 feet in length and from a few pounds to
perhaps 45 tons in weight. Some were _carnivorous_ (meat-eaters) but the
majority were _herbivorous_ (plant-eaters). Some were _bipedal_ (walked
on their hind-legs) while others were _quadrupedal_ (walked on all
fours), and although most of the dinosaurs were terrestrial in habitat,
aquatic and semi-aquatic forms were also present.
According to the structure of their hip bones, the dinosaurs have been
divided into two great orders. These are the Saurischia (forms with
lizard-like pelvic girdle) and the Ornithischia (dinosaurs with a
bird-like pelvic girdle).
[Illustration: Plate 43
Dr. Brown, R. T. Bird, and Dr. Schaikjer with the skull of
_Phobosuchus_, an extinct crocodile from the Cretaceous of Trans-Pecos
Texas.
Photograph courtesy of the American Museum of Natural History.]