A wallaby (/ˈwɒləbi/) is a small or middle-sized macropod native to Australia and New Guinea, with introduced populations in New Zealand, Hawaii, the United Kingdom and other countries. They belong to the same taxonomic family as kangaroos and sometimes the same genus, but kangaroos are specifically categorised into the four largest species of the family. The term 'wallaby' is an informal designation generally used for any macropod that is smaller than a kangaroo or a wallaroo that has not been designated otherwise. Although members of most wallaby species are small, some can grow up to approximately two metres in length (from the head to the end of the tail). Their powerful hind legs are not only used for bounding at high speeds and jumping great heights, but also to administer vigorous kicks to fend off potential predators. The tammar wallaby (Notamacropus eugenii) has elastic storage in the ankle extensor tendons, without which the animal's metabolic rate might be 30–50% greater. It has also been found that the design of spring-like tendon energy savings and economical muscle force generation is key for the two distal muscle–tendon units of the tammar wallaby (Macropus-Eugenii). Wallabies also have a powerful tail that is used mostly for balance and support. (Source: Wikipedia.org, CC BY-SA)