_Mylodon_ was one of the larger North American ground-sloths. Its teeth, without the protective enamel which is present among higher mammals, are restricted to the cheek region, and have the form of simple pegs; instead of being specialized they stand close to the extreme of generalization. The construction of the entire skeleton is massive, suggesting great strength with slow movements. The hands are well developed, provided with stout claws, and must have served the creature well as protection against attacks by predatory neighbors. We have some idea as to what caused the extermination of the ground-sloths in this particular region, but the complete disappearance of such a large and widely distributed group at the close of the Pleistocene period is a mystery that may never be explained. [Illustration: The Folsom, New Mexico, Bison (_Bison taylori_)] The saber-tooth cat, sometimes referred to as a tiger, was specialized as a meat eater though hardly as a hunting animal. In the La Brea region its principal food was probably the flesh of the sluggish ground-sloths. The size was equal to that of the African lion, with hind limbs slightly longer and the front legs more powerfully developed. The most remarkable characteristic is to be found in the development of the upper canine teeth and modifications of the skull which were necessary to enable the animal to use these teeth as weapons. In order to make the “sabers” effective it was necessary to get the lower jaws out of the way, and this was provided for in an unusual type of hinge which enabled the mouth to open wider than is possible in the case of the less specialized carnivores. Judging by all the structural features of the skeleton, _Smilodon_ could not have lived well on small animals, for it was not equipped to capture that kind of prey. It is evident that large mammals were preferred, and that the method of attack was to spring upon the victim and cling there with the powerfully developed fore limbs until the kill was completed by stabbing into a vulnerable spot. That the position of the large sabers near the front of the mouth interfered with normal feeding, is a reasonable conclusion. There are also anatomical features which lead to the belief that this carnivore was a blood sucker, perhaps more than it was meat-eater.