They are special in that nearly half of their fibula is fused with the tibia. This allows them to have great mobility and to run faster. They have a narrow, light skull with pronounced internal segmentation. The palatal openings of their skull are only as wide as the molar teeth. The ulna and the radius are of equal thickness and upper and lower arms are almost the same length.
Rabbits are very similar to many other mammals.
The compostion of their blood serum bears great similarity to that of the ungulates . Their proteins and nucleic acids tend to indicate a connection to the primates and tree shrews . They are no more closely related to rodents than they are to any other mammals. The cottontail rabbit species is located in three-fourths of the United States, except for the west. It can also be found in a small portion of southern Canada, all of Mexico, some of Central America, and the northern tip of South America.