Antelope Jackrabbits are nocturnal and crepuscular, and almost never vocalize. They are probably the fastest runners of their genus, with a top speed of 72 km per hour. They flash their white rumps somewhat as pronghorns do when they are running. Their ears are white on the outside, and longer than average. Typical of hares, and in contrast to rabbits, Antelope Jackrabbits give birth to well-developed young who are fully furred, with their eyes open, and able to hop.

Adaptation: As seen from the front and side, the spool-like shape of the main gliding surface of the elbow of the Antelope Jackrabbit, Lepus alleni, controls the movement of the forearm so that it can easily flex and extend but not twist. This is an adaptation to cursorial locomotion similar to what is found among other, very distantly related, running mammals.

Links:
Mammal Species of the World
Click here for The American Society of Mammalogists species account