Macropod is the common name for a group of marsupials belonging to the family Macropodidae. Their name is derived from the Greek words makros meaning large and poús or pod meaning foot (ie macro + pod = macropod). The key distinguishing features of all macropods are their triangular body shapes, large hind legs and feet, and disproportionately small front limbs. All have forward-facing pouches. And all, except for the musky rat-kangaroo, use hopping as their primary mode of locomotion. There are 73 species of macropods. They range in size from the 2 meter tall red kangaroo which weighs 90kgs to the tiny Musky rat-kangaroo which is just 30 cm tall and weighs about half a kilo.
Kangaroos are the biggest of the marsupials and the largest hopping animal in the world.
Red kangaroos are the largest marsupials and the largest hopping animal in the world. Standing up to 2 meters tall, it can hop at over 60kph and leap over obstacles 3 meters high.
Macropods vary in size considerably, but most have very large hind legs and feet, and long powerfully muscled tails which they use as a third leg during slow movements and as a support, like a tripod, when standing on their hind legs.
Almost all macropods are nocturnal. The reason for this night-time behaviour is that the daytime temperature in Australia can become extremely hot. So these animals have evolved to rest during the heat of the day and venture out at night. The musky rat-kangaroo is the only exception.
Macropods have four sets of molar teeth that continuously migrate from the rear of their jaws to the front as those in front ones wear down or fall out. When the last pair is too is worn down to be of use, the animal will not be able to feed itself and will die of starvation.
While most famous for their unusual hopping gait, macropods also have many other unique aspects to their biology, including embryonic diapause (suspended pregnancy),
The macropods comprise a diverse group of big-footed marsupials. The oldest branch of the family is Hypsiprymnodontidae containing only one living species, the Musky Rat-kangaroo. The second group is the relatively ancient Potoroidae which includes the potoroos and bettongs. The most recent group is Macropodidae, which include kangaroos, wallabies, pademelons, tree-kangaroos and the quokka.
Macropods are only found in Australia and New Guinea.
They can live in varied habitats from trees to the forest floor to open bush and shrub drylands. The majority of Australian macropods live in dry desert and shrub habitats and generally avoid colder climates. While macropods can swim, they are not aquatic. None live in waterways or in the oceans.
Almost all macropods are nocturnal. This means they only come out at night. The reason for this behaviour is that the daytime temperature in Australia can get extremely hot. So these animals have adapted to resting during the heat of the day and venturing out at night. The Musky rat-kangaroo seems to be the exception.
Macropods are generally solitary animals, only coming together for short-lived pair bonds during mating. They exhibit little permanent social organisation. Some of the larger macropods such as kangaroos and wallabies graze in groups called "mobs". However, these are not considered true social groups because there are no leaders or elders that exercise cohesion amongst members of the mob.
All macropods are the herbivores, eating only plant matter. Macropod metabolic rates are lower than that of comparable placental mammals. This means that they require less energy and as a result, they require less food to survive. They also require much less water than a comparably sized placental mammal.
All macropods (except the Musky rat-kangaroo) use hopping as their mode of locomotion. At slow speeds, they also use their tails like an additional leg.
Macropods have elongated and strong hind legs with large feet specially designed for hopping. They have perfected this mode of locomotion to make it one of the fastest and most efficient methods of terrestrial animal locomotion. Very little additional effort and energy are required to increase speed (compared to a horse or human for example) and to carry extra weight such as a large offspring in its pouch.
Macropods are marsupials and have many reproductive strategies that are suitable to the harsh Australian environment.
The female marsupial has three vaginas and two uteruses (uteri). The two outermost lateral sexual vaginas are used for sperm transportation to the two uteruses. Babies are born through the middle birth vagina. (See photo). By contrast, female placental mammals have only one uterus and one vagina.
With this unusual reproductive system, a female marsupial can be in a continuous state of pregnancy, with a fertilised egg in one uterus waiting to be released, a baby growing in the second uterus, one in her pouch and another hopping outside but coming to its mother for milk. Another unique feature of these animals is that during times of extreme drought and starvation the female marsupial can practice birth control by putting the babies growing in her uteruses "on hold", stopping their future development until conditions improve. This is called embryonic diapause. When the mother's pouch becomes free the next baby will be born and the fertilised egg will start developing into a new foetus.
Because of this multiple-offspring strategy and other adaptabilities unique to the marsupial, populations can increase rapidly when food is plentiful.
Most male marsupials have a bifurcated penis. That is, the penial shaft splits into two prongs at the end in order to enter the two separate lateral sexual vaginas of the female. Macropods, such as the kangaroo and wallaby, have a slender tapering single-shaft penis which enters only one of the lateral sexual vaginas. A marsupial's penis is located behind its scrotum. (Most animals have the penis located in front). When flaccid, the penis is withdrawn into the body. The Tasmanian tiger (thylacine) had a scrotum pouch in which it stored its scrotum and testicles for safekeeping.
Marsupial males have also adapted their sperm production to Australia's harsh environment. Because sperm production is energy-intensive, marsupial males have adopted three strategies. Adult kangaroos, wallabies, and rat-kangaroos produce sperm continuously and are therefore continuously fertile. However, in periods of extreme stress such as a drought when food is in short supply, their bodies shut down sperm production to conserve energy. Greater gliders only produce sperm during the mating season and at other times sperm production is shut down. An extreme strategy is that of the Antechinus where sperm is produced only once in the animal's lifetime, synchronised with the female's oestrus period (fertility period, comes into heat). After copulating as many times as possible during this time males exhaust themselves and die in a few days.
The marsupial egg descends from the female's ovary into a uterus where it is fertilized. Once fertilised, the egg is encased in a very thin shell similar to that of birds and reptiles. This shell is just a few microns thick and disintegrates when the egg reaches the third phase of gestation. A remnant from the evolutionary past this unusual characteristic is common amongst marsupial mammals. The gestation period for a marsupial is between 12 to 30 days and varies amongst the different types of marsupials.
As the time approaches for the young marsupial to be born the female marsupial cleans out its pouch by sticking her head into her pouch licking the inside of it clean. It then takes up a "birthing position" by sitting on its back with its tail between its legs and the hind legs extended straight forward. It also leans the trunk of its body forward. It then licks its birth canal opening possibly to stimulate the birth.
The young marsupial, ranging in size from no larger than a grain of rice to about the size of a jelly-bean, soon emerges from the birth canal. It is born blind, hairless, with stumpy forelimb and hardly any trace of its hind legs. Even though it is still so underdeveloped the young newborn has an excellent sense of direction, knowing which way is up and down, and also an acute sense of smell. Using its little forelimbs in a swimming motion, the young joey crawls laboriously up its mother's fur to the pouch. This journey takes it about three minutes. The joey's journey is made entirely by itself. The mother does not assist in any way. Once inside its mother's pouch, the joey quickly attaches itself firmly to a nipple in the pouch.
Once it has attached itself to its mother's nipple the young joey will stay hidden for up to six and a half months. Then it will start to tentatively pop its head out of its mother's pouch and observe the world around it. About two weeks later it will have gained enough confidence to venture out of the pouch and hop about close to its mother. However, if frightened it will immediately jump back into the safety of the pouch. By the time it is about 8 months old the joey no longer uses its mother's pouch.
The female marsupial can produce two types of milk depending on the joey it is feeding. The milk produced in the nipple on which an embryonic joey is attached will be different from the milk produced to feed a joey that has already left the pouch and only comes back to be weaned.