An order of extinct mesozoic reptiles, mostly of
   large size (whence the name). Notwithstanding their size, they present
   birdlike characters in the skeleton, esp. in the pelvis and hind limbs.
   Some walked on their three-toed hind feet, thus producing the large
   "bird tracks," so-called, of mesozoic sandstones; others were five-toed
   and quadrupedal. See Illust. of Compsognathus, also Illustration of
   Dinosaur in Appendix.