Kangaroos stand on large rear legs, using their long tail for added support. They have small front legs, with handlike paws that lack an opposable thumb. Hopping is their most unusual characteristic. Besides kangaroos and their relatives, no vertebrate bigger than ten pounds hops. At slow speeds, kangaroos walk awkwardly and inefficiently, using their front legs and tail. However, at speeds over fifteen miles per hour, they hop upright in a graceful motion that can be more energetically efficient than running by quadrupeds, whose energy use is proportional to their speed. Kangaroos increase their speed by lengthening their stride, while keeping their hop frequency constant, at little increased energy expenditure. They propel themselves by virtue of highly elastic legs which move in unison and use their long tails to provide balance.
As marsupials, kangaroos nurse their young (called joeys) in a pouch. Female kangaroos, half the size of males, have one-month gestations, which can be interrupted if a young is still suckling in the pouch or under adverse nutritional conditions. In these cases, the embryo goes into diapause, a form of "suspended animation," until hormonal signals permit development to resume. The newborn is highly immature, pink and naked, resembles a slug, and weighs less than 0.03 ounces. Using its front legs and a good sense of smell, it crawls from the birth canal into the pouch
The kangaroo's strong tail assists it in maintaining an upright, bipedal posture. It is the only mammal with a weight over ten pounds that hops as its mode of locomotion. (Adobe)
and attaches itself to one of four teats of the mammary gland. Over the next three months, it remains permanently attached to that teat and becomes fully developed. Depending on the species, joeys leave the pouch for the first time at six to ten months, permanently leave the pouch at eight to eleven months, and are weaned at eleven to eighteen months. Females are sexually mature at eighteen months to two years, although some males do not become so until they are four years old.
Kangaroos are herbivores, and all six species are grazing animals. Their teeth are suited to grasses rather than shrubs and trees. They are also very efficient in their use of water, making them suitable for the arid regions of Australia. Some species consume less than 10 percent the water sheep do under the same conditions. When temperatures are moderate, they can get all of their water from the plants that they eat. They are inac tive in the heat of the day and cool themselves by panting, sweating, and licking; the latter refers to the fact that they cover their front legs with saliva, which by evaporation cools not only their extremities but also their bodies via a dense network of blood vessels close to the surface. Kangaroos are among the most heat-tolerant of mammals. In addition, they have large, padded feet that compact the soil less than domesticated livestock.
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