Marsupial

The Marsupials are the members of the mammalian infraclass Marsupialia. Australasia and the Americas are home to all extant marsupials. The fact that most of these species carry their young in a marsupial pouch is a distinguishing feature. Kangaroos, wallabies, koalas, opossums, wombats, Tasmanian devils, and the extinct thylacine are among well-known marsupials. Dunnarts, potoroos, and cuscus are among lesser-known marsupials.

Marsupials generally represent the clade that has originated from the last common ancestors of the extant metatherians. Similar to other mammals in the Methatheria, these mammals also give birth to underdeveloped young ones that reside or take shelter in the pouch which is located in the mother’s abdomen for a certain amount of time and this could even last for a year. The Australian landmass is home to almost 70% of the world's 334 species. The remaining 30% are located in the Americas, mostly in South America, with thirteen in Central America and one north of Mexico.

The word Marsupial generally comes from, marsupium which is a technical term that means the abdominal pouch. The word is also borrowed from the Latin language which precisely means pouch.

In this article, we are going to discuss marsupial mammals, what is marsupial meaning, their description of the habitat, different types of marsupials, and also a few of the most important and frequently used questions related to the marsupials will be answered. 

Diversity in the Marsupials 

• The Metatherain mammals who are also known as the marsupials consist of 272 species. These are the nascient group of animals that are very diverse when we consider their body forms and they occupy an enormous range of ecological places around the world where they could live happily. 

• Most of the animal marsupials are found in Central and South America. Around 70 species of marsupials are found in Central and South America and around 200 species are found in Australia. The number of species is higher in Australia as many believe that millions of years ago all the species of the marsupials had made Australia as their home but as time passed and humans started to settle in Australia, few marsupial mammals had to travel to other parts of the world. 

• During the Cenozoic, radiation occurred on each of these continents, when placental rivals were few. The current marsupial fauna is quite varied, with some surprising similarities to placental animals. Kangaroos, for example, appear to have no placental mammal analogs in their life cycles and morphology. Even more amazing were past marsupial faunas.

• In the past, Australia was home to one of the largest marsupial mammals that ever lived such as rhinoceros-sized herbivorous, kangaroos which were nearly 10 feet tall, and carnivorous lions that had sharp and long canine teeth and retractable claws. 

• In South America, where simultaneous radiations of big placental herbivores may have prevented marsupials access to these herbivorous niches, marsupials inhabited several predator and rodent-like subcultures. On both continents, it appears that the invasion of placental animals is linked to a decrease in the quantity and variety of marsupials. However, it's uncertain if placental animals triggered marsupial extinction through competition or whether the apparent pattern of replacement is the consequence of chance historical occurrences.

Physical Description of the Marsupials 

• The marsupials differ from placental mammals in a number of ways. The palate of most marsupials is "fenestrated," meaning that it has wide gaps or holes in its bony surface. Almost all marsupials have their dentary angular process inflected or bent medially. The braincase is thin and tiny. When compared to placental animals of similar size, it has a tiny and simple brain. The jugal is a big bone that extends posteriorly to touch and becomes a component of the glenoid fossa. The lacrimal canal opens on the surface of the face rather than inside the orbital space because it is somewhat anterior to the orbit. The bullae aren't always ossified. When they exist, they are typically produced by alisphenoid extensions.

• The marsupials have the characteristics of the mammals such as the mammary glands, three ear bones, and true hairs on their bodies. Even though there are similarities there are also differences between the marsupials and the mammals. Other anatomical traits of marsupials include the front pouch, which holds numerous teats for the feeding of their young. Most contemporary marsupials lack ossified patellae, although epipubic bones are present. The corpus callosum, which connects the right and left hemispheres of the brain, is absent in marsupials and monotremes.

Skull and Teeth of the Marsupials 

• The skull of the marsupials is very unique when it is compared to the placental mammals. The skull of the marsupials is comparatively small and tight. In front of the orbit, holes are located and the cheekbones are very enlarged and it extends further to the rear. The lower jaw's angular extension is curved toward the center. Another distinguishing characteristic is the hard palate, which, unlike the foramina of placental animals, always has more openings. All taxa except wombats have a distinct number of incisors in the upper and lower jaws, which differs from that of placental mammals.

• The dental formula of the early marsupials from \[\frac{5.1.3.4}{4.1.3.4}\] which is per quadrant they have five maxillary or four mandibular incisors, one canine tooth, three premolars, and four molars and have a total of 50 teeth. Few taxa have the same original number of teeth which is 50 whereas in other groups the number of teeth has been reduced. 

• The dental formula for the kangaroos and the wallabies which come under Macropodidae is 3/1 – (0 or 1)/0 – 2/2 – 4/4. Marsupials have 40 to 50 teeth on average, which is substantially more than placental animals. The second set of teeth erupts as permanent teeth only at the 3rd premolar site and back; all teeth anterior to that emerge as baby teeth.

Torso of the Marsupials 

• The marsupial's skeleton has a few general features. Epipubic bones are seen extending forward from the pubic bone of the pelvis, in addition to other distinctive features in the development of the ankle. Because they are seen in males and pouchless animals, it is thought that they were initially used to aid in the muscular approach to hind leg mobility rather than for reproduction. This may be due to a unique characteristic of mammals, although epipubic bones may also be seen in monotremes.

• The reproductive organs of marsupials differ from those of placental animals. The reproductive tract is doubled in size for them. Females have two uteri and two vaginas, and before giving birth, a birth canal called the median vagina develops between them. A split or double penis lies in front of the scrotum in men.

• Most species have a pouch, although not all of them. Many marsupials have a permanent bag, whereas others acquire one during pregnancy, such as the shrew opossum, where the small marsupials are merely covered by skin folds or the mother's hair. The pouch can be arranged in a variety of ways to provide the best possible protection to the offspring. Many kangaroos that walk or climb on all fours have a pouch entrance in the front, whereas locomotive kangaroos have a pouch opening in the rear. Normally, only female water opossums have pouches, but the male water opossum has one as well, which he uses to store his genitalia when swimming or sprinting.

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Habitat 

• Marsupials are very much found in Australia and Australia has been a home for the most number of animal species and from that, we can deduce a point that it has favorable conditions to help the animals survive. Metatheria species can be found in a variety of habitats, from Australia's deserts and arid scrubland to South America's lush rainforests. These creatures may be found in a wide range of terrestrial environments throughout both continents. The only species are known in temperate North America to live in wet forests in their native habitat, although it is also found in towns and small cities. Metatherians have been developed to fill a number of requirements in a variety of environments. Many species are entirely terrestrial, some are arboreal, and at least one is semi-aquatic, the yapoks.

Geographic Range 

• As mentioned before more than 70 species of marsupials are found in Central and South America whereas more than 200 species of marsupials are found in Australia. In temperate North America, one species can be found which is the Virginia opossum. By the Middle Cretaceous, Metatheres had split from the lineage that led to eutherian (placental) mammals

• Early meta there’s diversification is considered to have occurred in North America, but by the middle Miocene, the lineage had been extinct on that continent, reappearing only when North and South America reconnected in the Pliocene. The earliest marsupials are thought to have looked like North American opossums and other Didelphidae relatives. Although there are a few fossil marsupials from Europe, Africa, and Asia, the group was never firmly established on those continents.

Reproduction in the Marsupials 

• Metatherians have a wide range of mating strategies. Throughout the year, many species are alone, only coming together to mate. Promiscuous mating systems are most likely to blame for this pattern of social behavior. Some species' males fight for access to many females. The best example of polygynous mating behavior is the Koalas. In highly sociable animals like whiptail wallabies, which may live in groups of up to 50 individuals, polygyny can also take the shape of male dominance hierarchies. Monogamy can also be seen in Metatheria. Petauroides Volans, for example, live in tiny family groupings made up of a mated pair and their young ones. 

• The placental mammals and the Marsupials differ greatly in their reproductive anatomy and pattern. The reproductive tracts of the marsupial females are fully doubled. The right and left vaginae do not fuse together to create a single body, as they do in all placental animals, and delivery occurs through a new midline channel called the pseudovaginal canal. The uteri of the right and left sides are likewise separated.

• In the developing marsupial embryo, the arrangements of the ducts that become the female reproductive tract are completely different in the marsupials when it is compared to the placental mammals. The few species of the female marsupials develop a pouch or marsupium in which the young are taken care of and basically they are nursed until they are ready to take care of themselves. The male penis is bifid or doubled, similar to the female vagina. In contrast to placental animals, the scrotum is located in front of the penis rather than behind it. The male marsupial penis is bifid or doubled, similar to the female vagina. In contrast to placental animals, the scrotum is located in front of the penis rather than behind it.

• Let’s keep aside all the differences between a marsupial male and female when they are compared to placental ones. The most unique and conspicuous difference between the marsupials and the placental mammals is in the degree of the development of the young ones at birth. The marsupial babies are very tiny when they are born which is that their weight is just one percent of the mother’s body weight and there are also cases where the young ones also weigh in milligrams. This is due to the fact that the young ones are born after a very short gestation period which is between 8 to 43 days and it also depends on the type of species. The placenta is formed in only a few selected species and even in the ones which have placenta the gestation period is very short. 

• Newborn marsupials are small and have barely begun to build functioning organs when they emerge from their mother's reproductive canal and crawl to the pouch. The forelimbs are highly developed because they are used to drag the young along the mother's abdomen by grabbing hairs with the forelimbs, while the hindlimbs are only paddles. The heart, kidneys, and lungs are all on the verge of failing. Even the brain is at an early stage of development. The pouch is where the majority of the development takes place, and the breastfeeding time is extended.

• It has been suggested that the reproductive pattern of the marsupial is very primitive for the metatherian and eutherian mammals. Many have argued and theorized in the past that the young ones must be born quickly before the mother’s immune system can respond and if it does, the immune system would consider the unborn baby as foreign tissue and will try to protect the body of the female marsupial from it. Most of the development takes place in the pouch where the baby is safe from maternal immune attacks. 

• Much of metatheres growth takes place after parturition when the young are nursing. Young grow inside the boundaries of a marsupium, or pouch, in roughly half of all marsupial species. In certain species, such as Macropus, weaning might take a year or longer. As a result, female metatheres devote very little energy and resources to pregnancy, whereas nursing necessitates a significant investment. 

• The pouch, which is a protective fold of skin in many species, may be permanent or form just when the reproductive cycle begins. In any scenario, resources must be allocated to the creation and maintenance of institutions that will safeguard the developing young. Once they are totally independent of the pouch, young typically do not associate directly with their mothers for more than a few weeks. This is true for both social and non-social animals.

The Behavior of the Marsupials

• As a consequence of evolving through the years and to fill ecological requirements, the marsupials have undergone or show a variety of behaviors in the wild. Arboreal, terricolous, or fossorial marsupials exist, and at least one species is semi-aquatic and examples of such are yapoks or water opossums. Walking, gliding, hopping, running, and swimming are some of the ways they move. Powered flight has not evolved among marsupials and so they cannot fly. 

• Marsupials can be diurnal, nocturnal, or crepuscular, and their activity patterns reflect this diversity. Some species may hibernate during the winter, while others stay active throughout the year. Some species live in groups, while others live alone.

Food Habits, Communication, and Predators 

• The marsupials could be omnivorous, insectivorous, carnivorous and herbivorous in nature. The best example of omnivorous marsupials is the American opossums, Australian possums, and the bandicoots. Marsupials such as the Kangaroos, koalas, and wombats are strictly herbivorous in nature and there are also several groups of marsupials that are either insectivorous or carnivorous and one such example is Dasyuridae.

• Vision, olfaction, hearing, and touch are all vital to Marsupial species in various degrees, just as they are to mammals in general. Communication may also take many other forms. Some marsupials use auditory signals to communicate, especially during mating or territorial battles. Many species have distinct color patterns that might reveal sex or species identity. Pheromones can be utilized to communicate reproductive receptivity as well.

• As the rule of the jungle, no one is excluded when it comes to predation and the same case is with the marsupials. They are also preyed on by many animals. Because marsupials are hardly ever top carnivores, they are preyed upon by a variety of mammalian, reptile, and avian predators.

Conservation Status of the Marsupials 

• Many marsupials are endangered or threatened. Over 200 species which are roughly two-thirds of all marsupials are now listed as being of considerable concern by the International Union for Conservation of Nature and Natural Resources (IUCN). Many populations have been substantially decreased due to habitat loss, overexploitation, and competition with alien species and livestock. As a direct result of human activities, a number of species have gone extinct in the last two centuries.