Kangaroo

Kangaroos are the largest marsupials alive today. Excluding specimens sent overseas, they are only found on the continent of Australia apart from some species in some areas of Papua New Guinea. There are at least sixty-nine species of kangaroo , which include wallabies and tree-kangaroos.

Description

Kangaroos have large ears on top of their small heads, a long snout, and short arms with clawed fingers. Their legs are strong, powerful, and are made for leaping. Their feet have four toes at the end of elongated metatarsi that they rest on when standing. They also have a powerful, thick tail that is used as support when standing, a third-leg when walking slowly, and for counterbalance while leaping. Like all Marsupials, female kangaroos have a pouch on their stomachs in which they carry their young.

Diet

Kangaroos are herbivores, eating grass, roots, and shrubs. They have a chambered stomach similar to sheep and cattle. They are able to regurgitate their food, chew it again as cud, and then swallow it for digestion.

Social Order

Kangaroos travel in mobs of about ten or more males and females. The leader of the mob, called a "boomer", is a male determined by age and size. The boomer has access to females in his mob for mating and will wander around the mob intimidating any other males who try to mate with his harem.

Reproduction

Like all marsupials, kangaroos lack a true placenta, the structure in a pregnant female's womb that provides nutrients for and removes waste from the growing embryo. Instead of a fully developed placenta, kangaroo females form a type of yolk sac in the womb. The embryo absorbs nutrients from this yolk sac for four to five weeks and then emerges from the birth canal, still in an embryo-like form but with well-developed forelimbs. The tiny animal crawls along its mother's body and into an abdominal pouch. Once inside, the offspring attaches firmly to a nipple, suckling milk. It remains there for several months until it is more fully formed and can move about on its own. The young kangaroo, sometimes called a joey, may remain with the mother, climbing into her pouch for nourishment or safety, until it is more than a year old. Most kangaroos produce a single young per litter. Depending on environmental conditions and food resources, one litter is typically born each year. Some kangaroo species living in dry regions have evolved the ability to breed whenever food and water resources are favorable. This may result in normal reproduction or no litters for several years if conditions are poor. The unpredictable nature of the availability of resources has led to the evolution of another specialized reproductive feature in some kangaroos. As soon as the tiny offspring emerges from the womb, the female is able to mate again. While the newborn suckles a nipple in the mother’s pouch, a fertilized egg begins developing in her womb. The development of the fertilized egg stops abruptly when the egg becomes a simple, hollow ball of about 100 cells, called a blastocyst. The blastocyst remains in a state of suspended development in the female's womb while the offspring in the pouch continues to grow. After the pouch offspring is more mature and is able to leave the mother’s pouch (up to six or seven months later), the blastocyst resumes development and soon emerges from the womb and moves into the now empty pouch. This reproductive feature, called embryonic diapause, enables kangaroos to care for up to three litters simultaneously during desirable conditions: an older, weaned offspring still under the mother's care, another maturing in the pouch, and a third in suspended development in the uterus. Should adverse conditions cause the weaned young to die, other offspring are still available for rearing.

Development of the Young in the Pouch

Kangaroos have adapted to the varied conditions across Australia in many ways. One of the most unusual, is the way females of some species can delay the progress of pregnancy. In this way the female is ready to give birth to a replacement for the young in her pouch if it dies early, or within a week of when it permanently leaves the pouch. This ability to delay births means that there can be up to 12 months between a mating and the birth of the young one resulting from that mating (when the normal gestation period is less than 35 days). It also means that the species can best respond to periods of drought and plenty.

Species which have this unusual ability normally mate again soon after the female gives birth. The tiny newly born kangaroo (less than 25 mm long) moves unaided into its mother's pouch and attaches itself to one of four teats. During the early stages of pouch life the young is permanently attached to the teat, but as it matures and begins to grow hair it also develops the ability to release and reattach itself to the teat.

In the late stages of pouch life, once it has a thin covering of fur, the young one begins to explore the outside world for increasing lengths of time until eventually it is old enough to be excluded permanently from the pouch. Complete weaning may take a number of months more after the young has permanently left the pouch. If the mother gives birth during this time, the newborn young will attach itself to a different teat to that being used by the older young. It is remarkable that when this happens the mother produces two different kinds of milk for the two different-aged young.

Origins

Consistent with their view that the fossil record as a whole does not support the evolutionary position, creationists state that there is a lack of transitional fossils showing an evolutionary origin of kangaroos. Rebecca Driver writes:

The Macropod family is alleged to have evolved from either the Phalangeridae (possums) or Burramyidae (pygmy-possums)...
However, there are no fossils of animals which appear to be intermediate between possums and kangaroos. Wabularoo naughtoni, supposed ancestor of all the macropods, was clearly a kangaroo (it greatly resembles the potoroos which dwell in Victoria’s forests). If modern kangaroos really did come from it, all this shows is the same as we see happening today, namely that kangaroos come from kangaroos, "after their kind."

According to the origins theory model used by young earth creation scientists, modern kangaroos are the descendants of the two founding members of the modern kangaroo baramin that were taken aboard Noah's Ark prior to the Great Flood. It has not yet been determined by baraminologists whether kangaroos form a holobaramin with the wallaby, tree-kangaroo, wallaroo, pademelon and quokka, or if all these species are in fact apobaraminic or polybaraminic.

After the Flood, these kangaroos bred from the Ark passengers migrated to Australia. There is debate whether this migration happened over land with lower sea levels during the post-flood ice age, or before the supercontinent of Pangea broke apart The idea that God simply generated kangaroos into existence there is considered by most creation researchers to be contra-Biblical.

Other views on kangaroo origins include the belief of some Australian Aborigines that kangaroos were sung into existence by their ancestors during the "Dreamtime" and the evolutionary view that kangaroos and the other marsupials evolved from a common marsupial ancestor which lived hundreds of millions of years ago.

In accordance with their worldviews, a majority of biologists regard evolution as the most likely explanation for the origin of species including the kangaroo.

External Links

• Kangaroo facts
• Answers About Kangaroos
• How did animals get from the Ark to places such as Australia?