Leslie Massey
Marsupials are a diverse group of mammals that give birth to underdeveloped young that continue to grow and develop in their mother's pouch. Australia boasts the most diverse population of marsupials in the world, with more than 200 different species. In the United States, the only marsupial that can be found is the Virginia opossum, which migrated from South America around 3 million years ago. This raises the question: should a small Australian marsupial, such as the kowari or quokka, be introduced to the United States?
| Characteristics | Values |
|---|---|
| Number of marsupial species in the US | 1 |
| Name of the marsupial species in the US | Virginia opossum |
| Marsupial species in Australia | More than 200 |
| Total number of marsupial species in the world | 334 |
| Diet of the Virginia opossum | Insects, small vertebrates, eggs, carrion, rats, mice, cockroaches, ticks |
| Habitat of the Virginia opossum | Forests, shrublands, urban environments, backyards, parks |
| Distinct cranial features of marsupials | Relatively small and compact skulls, frontal holes, enlarged cheekbones |
| Marsupials' unique reproductive strategy | Young are born in an undeveloped state and nurtured in a pouch on the mother's abdomen |
| Marsupials' evolutionary relationship with placentals | Marsupials and placentals split from a common ancestor in the Middle Jurassic-Early Cretaceous period |
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What You'll Learn
The Virginia opossum is the only marsupial in the United States
The Virginia opossum, also known as the North American opossum, is the only marsupial in the United States. It is a member of the opossum family found from southern Canada to northern Costa Rica. Its scientific name is Didelphis virginiana.
The Virginia opossum is the size of a domestic cat and is a solitary, nocturnal animal. It is commonly referred to as a "possum", although this term is sometimes used to refer to similar Australian marsupials. Opossums are native to Central America and the southern United States, and their range has expanded northward over the past century. They can now be found as far north as Ontario, Canada.
The Virginia opossum is one of the oldest surviving mammals on the planet, having existed for about 65 million years or more. Scientists believe that modern marsupials, including the opossum, may have descended from ancestors that originated in North America. Around 65-68 million years ago, many of these ancestors went extinct or migrated to South America, which is now home to about 100 marsupial species. The Virginia opossum is believed to have migrated north about 3 million years ago.
The Virginia opossum is known for its unique behaviour of playing dead when faced with danger to avoid predation. They also have a distinctive reproductive strategy, with female opossums giving birth to up to 20 young at a very early stage of development. The young must then find their way into the mother's pouch and attach to a teat to continue developing.
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Australian marsupials migrated from South America
Australia is known for its diverse marsupial population, with kangaroos, wallabies, koalas, wombats, and more. However, the idea that marsupials originated in Australia has been proven incorrect. A study published in the online journal PLoS Biology suggests that Australian marsupials evolved from a common ancestor in what is now South America.
This study, conducted by researchers at the University of Munster in Germany, examined large chunks of marsupial genomes for evolutionary clues. They analyzed the genome sequences of the South American opossum and the Australian tammar wallaby, looking at DNA features called retroposons, or "jumping genes," that are passed down from mother to offspring with very similar genetic sequences. This indicated that the two species shared a common ancestor, supporting the theory that ancient South American marsupials migrated to Australia.
The migration likely occurred over 80 million years ago when the continents were connected as part of the supercontinent Gondwana. This migration theory is further supported by the presence of similar cranial features and dental formulas between South American and Australian marsupials. The overall history of marsupials is one of circular migration, with the earliest identified species found in China, followed by movement to South America and then Australia.
While the Virginia opossum is the only marsupial species found in the United States today, it is believed to have migrated from South America, reinforcing the connection between South American and Australian marsupials. The Virginia opossum is one of the oldest surviving mammals, having existed for about 65 million years or more, and is believed to have migrated north around 3 million years ago when South America connected with North America.
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Marsupials have distinct cranial features
Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are native to Australasia, Wallacea, and the Americas. There are over 300 extant species of marsupials, with about 70% of these species concentrated on the Australian continent.
The Virginia opossum (Didelphis virginiana) is the only marsupial species found in the United States. This species is believed to have migrated north from South America around 3 million years ago. The Virginia opossum is one of the oldest surviving mammals, having existed for about 65 million years or more.
Marsupials exhibit distinct cranial features compared to placentals. Their skulls are typically small and compact, with frontal holes known as foramen lacrimale located at the front of the orbit. Marsupials have enlarged cheekbones that extend further towards the rear, and their lower jaw's angular extension (processus angularis) is bent towards the center.
The hard palate of marsupials contains more openings than that of placentals. Marsupials also have a unique dental structure. Most Australian marsupials outside the order Diprotodontia have a varying number of incisors between their upper and lower jaws. Early marsupials had a dental formula of 5.1.3.4/4.1.3.4 per quadrant, totaling up to 50 teeth. Some marsupials, like the opossum, retain this large number of teeth, while others have reduced counts.
In addition to their cranial features, marsupials are known for their reproductive strategy. Marsupials give birth to relatively undeveloped young, which are then nurtured within a pouch on the mother's abdomen. This pouch provides protection and allows the offspring to continue developing before living independently.
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Marsupials have a unique reproductive strategy
The reproductive strategy of marsupials involves giving birth to live young, but with a very short gestation period, resulting in underdeveloped offspring. This strategy offers a lower risk to the mother, as she can easily abandon the young at an early developmental stage and survive to try again later. This adaptability may have contributed to the successful migration of marsupials from North America to Australia via Antarctica, as they could cope with less stable environmental conditions.
Marsupials have a distinct reproductive anatomy compared to placentals. The female reproductive tract is bifid, meaning they have two uteri and two vaginas, with a birth canal forming between them during birth. In contrast, male marsupials typically have a bifurcated penis, separated into two columns. Additionally, most female marsupials possess an abdominal pouch, which can vary in its level of development. Some have well-developed pouches, while others have only skin folds around the mammary glands, and a few small marsupials lack a pouch altogether.
The young of marsupials are born in a relatively undeveloped state and are nurtured within the mother's pouch. This prolonged development within the pouch involves complex lactation, with genetic studies revealing insights into the local regulation of mammary physiology and neonatal programming. Marsupials exhibit a wide range of reproductive strategies, and their reproductive biology is highly varied. For example, some species, such as the dasyuridae, exhibit semelparity, where males almost completely disappear from the ecological landscape after mating, relying heavily on sperm storage in the female reproductive tract.
The Virginia opossum, native to the United States, is an example of a marsupial that utilises the pouch for nurturing its young. After the babies are developed enough to leave the pouch, the mother continues to carry them on her back for an additional month or two while they continue to nurse. This extended period of care ensures the survival of the underdeveloped young.
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Marsupials are native to Australasia, Wallacea and the Americas
Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are native to Australasia, Wallacea, and the Americas. Marsupials are characterised by their unique reproductive strategy, where the young are born in an underdeveloped state and are then nurtured within a pouch on their mother's abdomen. This process is known as "premature birth", and it allows the newborn to continue developing while attached to the nipples on the mother's lower belly.
In Australasia, marsupials are found in Australia, Tasmania, and New Guinea, as well as in the surrounding islands. Australia boasts the most diverse population of marsupials in the world, with over 200 species out of about 334 worldwide. The Tasmanian devil, wombat, and kangaroo are some of the well-known marsupials native to this region.
In the Americas, marsupials are found throughout South America, excluding the central and southern Andes and parts of Patagonia. They are also present in Central America and southern Mexico. The only marsupial species found in the United States is the Virginia opossum (Didelphis virginiana), which migrated north from South America around 3 million years ago. This species is widespread in the eastern United States and along the Pacific coast.
The evolutionary history of marsupials dates back to the Middle Jurassic-Early Cretaceous period when the first mammals with their distinctive mode of reproduction arose on the ancient southern supercontinent of Gondwanaland. Over time, the supercontinent broke up into separate continents, and the ancestors of marsupials evolved in isolation on the new continents of Australia and South America. Molecular and DNA analyses support a South American origin for marsupials, with Australian marsupials descending from a single migration event across the Antarctic land bridge.
The presence of marsupials in two seemingly disconnected parts of the world, Australasia and the Americas, has sparked curiosity. This distribution can be explained by the movement of the southern continents and the migration of species. Marsupials likely originated in South America during the Jurassic when Australia and South America were connected via Antarctica. As the continents drifted apart, the marsupial populations in each isolated continent evolved and diversified independently. The formation of the Isthmus of Panama allowed for the migration of opossums into North America, leading to their presence in the northern hemisphere.
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Frequently asked questions
The only marsupial in the United States is the Virginia opossum (Didelphis virginiana), which is also found in Central and North America.
Marsupials are a diverse group of mammals that give birth to underdeveloped young that continue to grow and develop in their mother's pouch. This is in contrast to placental mammals, such as humans, dogs and whales, where the young are more developed at birth.
Yes, opossums have a very adaptable diet, which makes it easy for them to live in a range of environments, from urban to suburban to wilderness areas. They also help to control pest populations, such as rats, mice, cockroaches and ticks.
