Dimetrodon was an apex predator, among the largest of its day. It grew to up to 3½ meters (11 feet) in length and weighed 250 kilograms (550 lbs) (the size of a big cat). The name Dimetrodon means 'two measures of teeth', so named because it had a large skull with two different types of teeth (shearing teeth and sharp canine teeth), unlike reptiles. Dentition showing this differentiation of teeth is called heterodonty. It walked on four side-sprawling legs like a crocodile and had a large tail. Dimetrodon may have moved in a manner similar to present-day lizards. In addition, Dimetrodon was not a dinosaur, despite being often incorrectly classed with them. Rather, it is classified as a pelycosaur. Fossils of Dimetrodon have been found in North America and Europe, as well as significant discovery of Dimetrodon footprints in southern New Mexico by Jerry MacDonald. As well as their sheer size and power, Dimetrodon had a killer edge. As a protomammal, they evolved specialized teeth. Incisors shear of chunks of flesh. Serrated canines cut and slice. Humans have inherited these same meat-eating teeth, although we use a smaller version in our mouths today. There are several species of Dimetrodon, and the information given above refers to the type species only.