_Ornitholestes._ In contrast with the _Allosaurus_ and _Tyrannosaurus_ this skeleton represents the smaller and more agile carnivorous dinosaurs which preyed upon the lesser herbivorous reptiles of the period. These little dinosaurs were probably common during all the Age of Reptiles, much as the smaller quadrupeds are today, but skulls or skeletons are rarely found in the formations known to us. The _Anchisaurus_, _Podokesaurus_ and other genera of the Triassic Period have left innumerable tracks upon the sandy shales of the Newark formation, but only two or three skeletons are known. A cast of one of them is exhibited here. The original is preserved in the Yale Museum. In the succeeding Jurassic Period we have the _Compsognathus_, smallest of known dinosaurs, and this _Ornitholestes_ some six feet long. A cast of the _Compsognathus_ skeleton is shown, the original found in the lithographic limestone of Solenhofen is preserved in the Munich Museum. The _Ornitholestes_ is from the Bone-Cabin Quarry in Wyoming. The forefoot with its long slender digits is supposed to have been adapted for grasping an active and elusive prey, and the name (_Ornitho-lestes_ = bird-robber) indicates that that prey may sometimes have been the primitive birds which were its contemporaries. In the Cretacic Period, there were also small and medium sized carnivorous dinosaurs, contemporary with the gigantic kinds; a complete skeleton of _Ornithomimus_ at the entrance to the Dinosaur Hall finely illustrates this group. In appearance most of these small dinosaurs must have suggested long-legged bipedal lizards, running and walking on their hind limbs, with the long tail stretched out behind to balance the body. From what we know of their tracks it seems that they walked or ran with a narrow treadway, the footsteps almost in the middle line of progress. They did not hop like perching birds, nor did they waddle like most living reptiles. Occasionally the tail or fore feet touched the ground as they walked; and when they sat down, they rested on the end of the pubic bones and on the tail. So much we can infer from the footprint impressions. The general appearance is shown in the restorations of _Ornitholestes_, _Compsognathus_ and _Anchisaurus_ by Charles Knight. [Illustration: Fig. 17.--Skeleton of _Ornitholestes_ a small carnivorous dinosaur of the Jurassic period. American Museum No. 619.] [Illustration: Fig. 18.--Restoration of _Ornitholestes_, by C.R. Knight under direction of Professor Osborn. _After Osborn_]