Superfamily MacropodoideaThis is a diverse but recognizable groups of marsupials. There are at least 65 species of kangaroos, with most being found in Australia, and a small, but unique, assortment in New Guinea. Despite the varied range of forms, there is a common body plan to all members of this group. They are often referred to as the 'macropods' from the scientific name of the superfamily, which translates from the Greek to mean 'big -footed' (Egerton 1997). This term describes one of their most defining and distinctive characteristics; long toes on big feet, on the end of strong hindlegs. This physical feature allows, especially in the larger species, for a fast and efficient hopping gait. In contrast, the arms and hands are generally much shorter and weaker. Historically, there have been many different families of kangaroos. Some of these contained members that were probably carnivorous in habit (Archer et al 200). All living macropods are herbivorous, with the smaller ones being a little more omnivorous, and the larger ones being more standard grazers (Stahan 1998). All of the extant species belong to two families; the smaller, more primitive potoroids ('rat kangaroos', 'potoroos', 'bettongs'), and the generally larger and more recently evolved macropodids (kangaroos and various wallabies).
Script: Courtesy of Damon Ramsey BSc.(Zool) Biologist Guide
Kangaroo Hopping: Locomotion in the Macropodoids
One of the first features most people associate with kangaroos is the hopping. - As far as we know, this is a completely unique mode of transport in animals of this size, and according to the fossil record, has never occurred in any other animal at any other time in the history of life on Earth.
Due to the energy stored in the elastic tendons, the 'bouncing' locomotion is actually very efficient. In fact, it has been measured at being more efficient than galloping in equivalent sized mammals at certain speeds (Strahan and Cayley 1995). It also assists in reducing the energy used in breathing, by coordinating in and out breaths with the upwards compression and downward dropping of the gut during jumping. When moving at slower speeds, kangaroos use an equally unique 'pentapedal' locomotion that involves the two hindlegs, the two weaker forelegs and pushing with the tail (Egerton 1997). Due to their unique anatomy, kangaroos generally don't 'walk' backwards as four legged mammals can, (this is said to be one of the reasons kangaroos are symbolically represented on the Australian coat of arms). Equally, they do not generally move their legs independently, except when swimming or lying down (Strahan 1998).
Script: Courtesy of Damon Ramsey BSc.(Zool) Biologist Guide
The sex life and reproductive cycle of the Macropodoids Males of the more sociable kangaroos and wallabies may act aggressively towards each other, even fighting, to gain the right to females. The males approach the female from behind, often stroking the tail. Females of almost all species of macropodoids lack a specific mating season and therefore can be potentially receptive all year around, depending on conditions and young in development. All species have a well-developed pouch that opens forwards, and with muscles at the top that can lock the young in or out. Even though the pouch covers four teats, all but one species give birth one at a time (Strahan 1998). However if conditions are right, they can continuously produce young, one after another, for their entire life (Strahan 1998). This often results in the mother kangaroo having three offspring at any one time, all at different stages; an embryo inside, a joey in the pouch, and a young by the side (Strahan and Cayley 1995). This is when the multiple teats are used; the different teats actually produce different types of milk for the differently aged young. Another interesting feature of this reproductive cycle is the condition known as 'embryonic diapause', found in the macropodoids and a few other types of mammals (Strahan 1998). The female kangaroo can mate and fertilize immediately after birth, but can then put 'on hold' the development of the embryo, dependent on the progress of the current pouched young (Strahan 1998). This allows for the quick replacement of young, for the 'frozen' embryo will resume development if the pouched young dies (Strahan 1998).
Script: Courtesy of Damon Ramsey BSc.(Zool) Biologist Guide
The ‘Rat-kangaroos’, 'Bettongs', and 'Potoroos': Family Potoroidae Of the two families of kangaroos, the Potoroids are considered the more primitive. Kangaroos are thought to have evolved from a possum-like ancestor, and thus the potoroids retain more 'primitive' possum-like conditions than their larger wallaby and kangaroo relatives. They have less developed hind legs and shorter feet than their 'big-foot' cousins, and being closer in evolutionary terms to their possum-like ancestors, the potoroids also retain slightly prehensile (climbing) tails from their arboreal ancestors. Potoroids are much more omnivorous in their diet than the larger wallabies and kangaroos. They generally cannot digest grass like their larger stomached relatives, but eat 'easier' food such as fruit, tubers, fungi, insects and even dead animals (Strahan 1998). There are also some behavioural differences between the smaller potoroids and the bigger macropods. Unlike the bigger kangaroos, which essentially plonk down on the ground or rest up against a tree to snooze, the smaller, more vulnerable potoroids make nests (Strahan 1997). These are constructed out of plant materials such as grasses and fallen branches. They use their grasping 'possum-like' tail to carry material for their nest making. The sight of a small kangaroo bounding through the undergrowth with a curled tail full of sticks is quite an odd sight indeed. Apart from reproduction and raising young, potoroids are not considered gregarious, and are usually seen scampering alone along the ground. Currently, there are about ten species of potoroids in Australia (Strahan 1998). Being an older lineage than the larger kangaroos, there were many more and varied genera and species in prehistoric times (Archer et al 2000). In more recent times they have suffered in both terms of abundance and species diversity by the clearing of land by Europeans, and the introduction of competitive rabbits and predatory cats, dogs and foxes (Egeton 1997). In fact, Strahan and Cayley (1995) contend that no marsupial group has suffered more than the potoroids since European settlement; they observe that two species are extinct, three have suffered massive range reductions, one is rare, and that only three are considered secure.
Script: Courtesy of Damon Ramsey BSc.(Zool) Biologist Guide
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Eastern Grey Kangaroo
Rock Wallaby
Swamp Wallaby