Macropod

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Macropods[1]
Red-necked Wallaby
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Infraclass: Marsupialia
Order: Diprotodontia
Suborder: Macropodiformes
Family: Macropodidae
Gray, 1821
Genera
A red-necked wallaby
A red-necked wallaby

Macropods are marsupials belonging to the family Macropodidae, which includes kangaroos, wallabies, tree-kangaroos, pademelons, and several others. Prior to European settlement, there were about 53 species of Macropods. Today, six species have since become extinct. Another 11 species have been greatly reduced in numbers.

Contents

[edit] Physical description

Macropods are herbivorous: some are browsers, but most are grazers and are equipped with appropriately specialised teeth for cropping and grinding up fibrous plants, in particular grasses and sedges. In general, macropods have a broad, straight row of cutting teeth at the front of the mouth, no canine teeth, and a gap before the molars. The molars are large and, unusually, do not appear all at once but a pair at a time at the back of the mouth as the animal ages, eventually becoming worn down by the tough, abrasive grasses and falling out. Most species have four molars and, when the last pair is too worn to be of use, they starve.

Like the eutherian ruminants of the northern hemisphere (sheep, cattle, and so on), macropods have specialised digestive systems that use a high concentration of bacteria protozoans and fungi in the forestomach to digest plant material. The details of organisation are quite different, but the end result is somewhat similar.

Macropods vary in size considerably but most have very large hind legs and a long, powerfully muscled tail. The term macropod comes from the Greek for "long foot" and is appropriate: most have a very long, narrow hind foot with a distinctive arrangement of toes: the fourth toe is very large and strong, the fifth toe moderately so, the second and third are fused and the first toe is usually missing. The short front legs have five separate digits. Some macropods have 7 carpal bones instead of the usual 8 in mammals[1]. All have relatively small heads and most have large ears, except for tree-kangaroos, which must move quickly between tight branches. The young are born very small and the pouch opens forward.

The unusual development of the hind legs is optimised for economical long distance travel at fairly high speed. The famous kangaroo hop is not simply a matter of having strong legs: kangaroos and wallabies have a unique ability to store elastic strain energy in their tendons. In consequence, most of the energy required for each hop is provided "free" by the spring action of the tendons (rather than by muscular effort). The main limitation on a macropod's ability to leap is not the strength of the muscles in the hindquarters: the greatly elongated foot provides enormous leverage and the key factor is the ability of the joints and tendons to stand up under the strain of hopping.

In addition, there is a linkage between the hopping action and breathing. As the feet leave the ground, air is expelled from the lungs by what amounts to an internal piston; bringing the feet forward ready for landing fills the lungs again, providing further energy efficiency. Studies of kangaroos and wallabies have demonstrated that, beyond the minimum energy expenditure required to hop at all, increased speed requires very little extra effort (much less than the same speed increase in, say, a horse, a dog, or a human), and also that little extra energy is required to carry extra weight — something that is of obvious importance to females carrying large pouch young.

The ability of larger macropods to survive on poor-quality, low-energy feed, and to travel long distances at high speed without great energy expenditure (to reach fresh food supplies or waterholes, and to escape predators) has been crucial to their evolutionary success on a continent that, because of soil fertility and low, unpredictable average rainfall, offers only very limited primary plant productivity.

[edit] Classification

Tree-kangaroos have smaller ears for easier maneuvering between tree branches, and much longer tail.
Tree-kangaroos have smaller ears for easier maneuvering between tree branches, and much longer tail.
Five 'legs' for moving slowly while browsing: the forelimbs and muscular tail take the animal's weight while the hind legs are brought forward: a Red Kangaroo.
Five 'legs' for moving slowly while browsing: the forelimbs and muscular tail take the animal's weight while the hind legs are brought forward: a Red Kangaroo.
A pademelon from Tasmania. Although obscured by fur, most of this macropod's lower body consists of legs.
A pademelon from Tasmania. Although obscured by fur, most of this macropod's lower body consists of legs.
A pademelon from Port Douglas, Queensland area eating a slice of sweet potato. Although normally grazing straight from the ground, a macropod would eat a treat in small bites while holding it in its hands.
A pademelon from Port Douglas, Queensland area eating a slice of sweet potato. Although normally grazing straight from the ground, a macropod would eat a treat in small bites while holding it in its hands.
A Forester Kangaroo "flying" over a puddle in Narawntapu National Park, Tasmania
A Forester Kangaroo "flying" over a puddle in Narawntapu National Park, Tasmania

There are two subfamilies in the Macropodidae family: the Sthenurinae was highly successful in the Pleistocene but is now represented by just a single species, and a vulnerable one at that, the Banded Hare-Wallaby; the remainder, about 60 species, makes up the subfamily Macropodinae.

[edit] See also

[edit] References

  1. ^ a b Groves, Colin (16 November 2005). in Wilson, D. E., and Reeder, D. M. (eds): Mammal Species of the World, 3rd edition, Johns Hopkins University Press, 58-70. ISBN 0-801-88221-4. 
  2. ^ Haaramo, M. (2004-12-20). Mikko's Phylogeny Archive: Macropodidae - kenguroos. Retrieved on 2007-03-15.

[edit] External links

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