Log In Start studying!

Select your language

Suggested languages for you:
StudySmarter - The all-in-one study app.
4.8 • +11k Ratings
More than 3 Million Downloads
Free
|
|

Marsupials

Marsupials

If you’ve ever seen a kangaroo–whether in person, on the TV, or over the internet–you have probably noticed its distinctive pouch, where it holds its young. Have you ever wondered what purpose the pouch serves?

Kangaroos are marsupials, a group of mammals whose offspring are born prematurely and develop outside the mother’s body. The pouch protects the vulnerable young, which are just about the size of a honeybee at birth.

Read on to learn more about the definition, characteristics, and evolutionary history of marsupials!

What is the Definition of Marsupials?

Mammals are vertebrates with mammary glands which produce milk for offspring. There are around 5,300 extant species of mammals on Earth.

Along with monotremes (egg-laying mammals, such as platypus and echidnas) and eutherians (placental mammals with a long gestation period), marsupials are one of the three major lineages of mammals.

The definition of marsupials is shown below.

Marsupials are mammals whose young are born prematurely and continue development outside the mother’s body; specifically, they are attached to the nipples on the mother’s lower belly, where they will continue to develop. Many marsupials, like the wallaby and the kangaroo, are known for their prominent pouch.

What are Some Examples of Marsupials?

There are over 330 species of marsupial extant and around 250 of these species are native to Australia, New Guinea, and neighboring islands, where they make up most of the native mammals there.

These range in size from as small as a mouse, like the long-tailed planigale (Planigale ingrami), to larger than an adult human, like the red kangaroo (Osphranter rufus). Other examples of marsupials include bandicoots, cuscus, koalas, opossums, and wombats.

Around 70 species live in South and Central America, while one species–the Virginia opossum (Didelphis virginiana)–is native to the United States and Canada.

What are the Different Types of Marsupials?

Extant marsupials can be divided into three American orders and four Australasian orders (Fig. 1).

  • The American orders are:

    • Didelphimorphia (opossums);

    • Microbiotheria (monitos del monte); and

    • Paucituberculata (shrew opossums).

  • The Australasian orders are:

    • Dasyuromorphia (carnivorous marsupials);

    • Diprotodontia (kangaroos, possums, and koalas);

    • Notoryctemorphia (marsupial mole); and

    • Peramelemorphia (bandicoots).

Note that this is just one way of classifying them. Their evolutionary relationships– especially the exact phylogenetic position of Microbiotheria and Notoryctemorphia–are still under contention due to the limited amount of molecular and fossil evidence,

While they are taxonomically less diverse than eutherians (which have a total of 19 orders), marsupial species are just as morphologically and ecologically diverse.

Marsupial structure varies according to the ecological niches that they fill.

  • Burrowing marsupials, like marsupial moles and wombats, have powerful foreclaws that they can use to tunnel into the ground for food and shelter.

  • Gliders (or flyingpossums) have a membrane attached to the forelegs and hind legs, allowing them to glide down from a high perch. The wateropossum, which inhabits tropical rivers, streams, and lakes, is semiaquatic and has webbed feet.

Marsupial feeding habits are just as diverse as the niches they occupy.

  • Dasyurids, a group that includes the Tasmanian devil, feed primarily on insects and other small animals.

  • Wombats and many other marsupials feed only on plants and plant materials. For instance, the honey possum, along with other marsupials, feeds on the nectar of flowers and serves as a pollinator.

What are the Distinguishing Characteristics of Marsupials?

A marsupial can be distinguished from other mammals by the premature birth of its young, which completes its development while nursing. The young–in its vulnerable embryonic condition–makes its way from the mother’s birth canal to the nipples, where it finds shelter, warmth, and nourishment.

It stays securely attached to the nipples for weeks or months, a duration roughly comparable to the latter stages of fetal development in a eutherian mammal’s womb. After this stage, they are weaned and begin to look after themselves.

A red kangaroo is prematurely born just 33 days after fertilization. When it’s born, it’s just about the size of a honeybee! Its back legs are underdeveloped and look just like tiny buds. Its front legs are just strong enough to allow it to crawl into the pouch that opens in front of its mother’s body. If it is lucky enough to survive, it can grow up to 1.8 meters (or 5 feet and 10 inches) tall!

The marsupial reproductive anatomy is also unique to the group:

  • All female marsupials have a pair of lateral vaginae that each open into a common cavity called the urogenital sinus, which then empties into a short chamber called cloaca that connects to the intestinal tract. They also have two uteri (Fig. 2).

  • In male marsupials, the testes are found in front of the penis.

Do all Marsupials have a Pocket?

In most species, the developing young are held in a maternal pouch called marsupium, which is a layer of skin that covers the nipples.

However, note that the marsupium is not a universal feature: while many marsupials have a prominent pouch, some only have remnants of a pouch, while others do not have a covering over their nipples at all.

How are Marsupials Similar to and Different from Monotremes and Eutherians?

Marsupials are similar to other mammals in that they have hair and mammary glands.

Marsupials share some characteristics with eutherians that distinguish them from monotremes: they both have higher metabolic rates than monotremes, they have nipples that provide milk, and, instead of laying eggs, they both give birth to live young, with the embryo developing within the mother’s uterus. They also both have a placenta.

Yes, that means, contrary to popular misconception, eutherians are not the only mammals with a placenta. Marsupials also have a placenta, but it develops late into pregnancy, giving them a shorter gestation period. Furthermore, their placenta is composed of tissues that are different from those of eutherians.

That means the difference between marsupials and eutherians is not one of having a placenta or not, but rather one of the relative importance given to placentation and lactation to nurture the developing young:

  • In eutherians, the mother invests a roughly equal amount of energy in rearing its young before birth via placentation and after birth via lactation.

  • In marsupials, gestation is brief, and the placenta develops late into pregnancy. Lactation is extended and takes place in multiple stages, with the milk composition changing as the offspring grows (essentially performing the function of the eutherian placenta).

Gestation refers to the period in which an embryo is held within the mother's body.

Lactation refers to the secretion of milk via mammary glands.

In Australia, there are cases where eutherians and marsupials seem to have undergone convergent evolution; that is, by occupying similar ecological niches, they have shared traits that evolved separately. This is why both groups have species that burrow, glide, or consume insects despite being two distinct evolutionary lineages.

What is the Evolutionary History of Marsupials?

Before true mammals emerged, there were synapsids: four-limbed terrestrial vertebrates that lacked hair, had a sprawling gait, and laid eggs. They had a single temporal fenestra, a hole found behind the eye socket on each side of the skull.

Over the course of 100 million years, mammalian features gradually surfaced in the jaw of succeeding lineages of early non-mammalian synapsids.

During the Permian period, synapsids evolved into massive herbivores and carnivores, and for a while they dominated the tetrapod community. Their diversity sharply declined during the Triassic period (around 252-201 million years ago), but more and more mammal-like synapsids began to emerge. These synapsids were small, hairy, and ate insects. They also had a relatively high metabolic rate. They also still laid eggs.

True mammals first emerged during the Jurassic period around 201 to 145 million years ago. During this time, they diversified into many short-lived lineages. They coexisted with dinosaurs in the Jurassic and Cretaceous periods.

However, these early mammals were different from the mammals we know today. They were neither dominant nor abundant. In fact, they were really small: most of them measured no longer than a meter. Their diminutive size could be attributed to dinosaurs occupying the ecological niches of large-bodied animals.

In the early Cretaceous (around 140 to 100 million years ago), the three major mammal lineages emerged all over the world: monotremes, marsupials, and eutherians. Monotremes diverged from other mammals around 200 million years ago. Marsupials and eutherians diverged from a shared ancestor around 130 million years ago.

Ancestral marsupials are thought to have migrated to Australia and the nearby islands on land. Keep in mind that Australia used to be connected to South America and Antarctica as part of Gondwana, an ancient supercontinent that existed over 600 million years ago and broke up in stages starting 180 million years ago (Fig. 3).

Alongside the breakup of supercontinent Gondwana, another event drove evolutionary change in mammals: the extinction of large non-avian dinosaurs, pterosaurs (flying reptiles), and marine reptiles in the late Cretaceous period (around 100 to 66 million years ago).

Mammals underwent adaptive radiation--the process in which a group of organisms diversifies into forms to fill different ecological niches--giving rise to large predators and herbivores, as well as flying and aquatic species.

By 65 million years ago, the breakup of Gondwana had separated present-day Australia and New Guinea from other continents, resulting in the diversification of Australasian marsupials in isolation from eutherians that began adaptive radiation on other continents.

It is important to note that up until around 10,000 years ago, Australia, New Guinea, Sulawesi, and some neighboring islands were still connected as part of the Sahul continent. The Sahul continent was separated from Sundaland (present-day Java, Borneo, Sumatra, and neighboring islands) by water trenches, typically referred to as the Wallace Line.

For this reason, Australasian marsupials are typically found in Australia, Sulawesi, the Maluku Islands, and New Guinea, which are all east of the Wallace Line, but not in Borneo, Sumatra, or Java. In contrast, tigers, elephants, non-human apes, and rhinos are typically only found west of the Wallace Line.

The Wallace Line was named after Alfred Russel Wallace, who studied and recognized the stark contrast between the fauna of Southeast Asia and those of Australia and New Guinea.

Likewise, South and North America had been connected by the Panamanian isthmus (an isthmus is a narrow strip of land) up until 3 million years ago. This land bridge allowed for the movement of animals, including marsupials. This is believed to be the reason for the emergence of the sole North American marsupial: the Virginia opossum.

Marsupials - Key takeaways

  • Along with monotremes and eutherians, marsupials are one of the three major lineages of mammals.
  • Marsupials are mammals whose young are born prematurely and continue development outside the mother’s body.
  • Their gestation is brief, and the placenta develops late into pregnancy. Lactation is extended and takes place in multiple stages, with the milk composition changing as the offspring grows.
  • There are over 330 species of extant marsupials.
  • Most marsupials are found in Australia and neighboring islands, while others are found in South and Central America. One is native to North America and Canada.

References

  1. Reece, Jane B., et al. Campbell Biology. Eleventh ed., Pearson Higher Education, 2016.
  2. “Marsupial | Definition, Characteristics, Animals, and Facts.” Encyclopedia Britannica, www.britannica.com/animal/marsupial. Accessed 7 Oct. 2022.
  3. “Marsupial Mammals.” University of California Museum of Paleontology, ucmp.berkeley.edu/mammal/marsupial/marsupial.html. Accessed 7 Oct. 2022.
  4. Larry Vogelnest, Chapter 33 - Marsupialia (Marsupials), Editor(s): R. Eric Miller, Murray E. Fowler, Fowler's Zoo and Wild Animal Medicine, Volume 8, W.B. Saunders, 2015, Pages 255-274, ISBN 9781455773978, https://doi.org/10.1016/B978-1-4557-7397-8.00033-5. (https://www.sciencedirect.com/science/article/pii/B9781455773978000335)
  5. Abbot P, Capra JA. What is a placental mammal anyway? Elife. 2017 Sep 12;6:e30994. doi: 10.7554/eLife.30994. PMID: 28895533; PMCID: PMC5595430.
  6. “RED KANGAROO.” Billabong Sanctuary - Australian Native Wildlife Park Townsville, 6 Mar. 2018, www.billabongsanctuary.com.au/red-kangaroo.
  7. Maria A. Nilsson, Ulfur Arnason, Peter B.S. Spencer, Axel Janke, Marsupial relationships and a timeline for marsupial radiation in South Gondwana, Gene, Volume 340, Issue 2, 2004, Pages 189-196, ISSN 0378-1119, https://doi.org/10.1016/j.gene.2004.07.040. (https://www.sciencedirect.com/science/article/pii/S0378111904004548)
  8. Nilsson MA, Churakov G, Sommer M, Tran NV, Zemann A, Brosius J, Schmitz J. Tracking marsupial evolution using archaic genomic retroposon insertions. PLoS Biol. 2010 Jul 27;8(7):e1000436. doi: 10.1371/journal.pbio.1000436. PMID: 20668664; PMCID: PMC2910653.
  9. Meredith, Robert, et al. “A Phylogeny and Timescale for Marsupial Evolution Based on Sequences for Five Nuclear Genes.” J Mammal Evol, 2007, https://doi.org/10.1007/s10914-007-9062-6.
  10. “Natural History Collections: Origin and Evolution of Marsupials.” Natural History Collections: Origin and Evolution of Marsupials, www.nhc.ed.ac.uk/index.php?page=493.168.256. Accessed 7 Oct. 2022.
  11. J.A. Sharp, K. Menzies, C. Lefevre, K.R. Nicholas, Milk | Milk of Monotremes and Marsupials, Editor(s): John W. Fuquay, Encyclopedia of Dairy Sciences (Second Edition), Academic Press, 2011, Pages 553-562, ISBN 9780123744074, https://doi.org/10.1016/B978-0-12-374407-4.00516-1. (https://www.sciencedirect.com/science/article/pii/B9780123744074005161)
  12. Thomas, Nicholas. “From Sunda to Sahul | Natural History Magazine.” From Sunda to Sahul | Natural History Magazine, www.naturalhistorymag.com/features/113822/from-sunda-to-sahul. Accessed 8 Oct. 2022.

Frequently Asked Questions about Marsupials

5 examples of marsupials are kangaroos, koalas, wombats, opossums, and bandicoots.

A mammal is considered a marsupial if its young are born prematurely and continue development outside the mother’s body. 

Marsupials are mammals, but not all mammals are marsupials. Marsupials are a distinct mammalian lineage whose females give birth to premature young, which continue to develop outside of its mother's body.  

Humans are eutherians or placental mammals.

The key difference between a rodent and a marsupial lies in their embryonic development: rodents are eutherians, so their gestation and lactation periods are similar, while marsupials (a group that includes kangaroos, opossums, and koalas) have shorter gestation and longer lactation periods.

Final Marsupials Quiz

Question

What are the three major mammal lineages?

Show answer

Answer

Monotremes, marsupials, and eutherians

Show question

Question

What are marsupials?

Show answer

Answer

Marsupials are mammals whose young are born prematurely and continue development outside the mother’s body; specifically, they are attached to the nipples on the mother’s lower belly, where they will continue to develop.

Show question

Question

Where do marsupials naturally occur?

Show answer

Answer

Marsupials are found in Australia and its neighboring islands as well as in South and Central America. One marsupial species is native to North America and Canada.

Show question

Question

Describe the feeding habits of marsupials.

Show answer

Answer

Marsupials have a diverse feeding habit: some, like the Daysurids, are carnivorous or insectivorous, while others are herbivorous or nectivorous. 

Show question

Question

These mammals have a placenta.

Show answer

Answer

Marsupials

Show question

Question

What makes marsupials mammals?

Show answer

Answer

Marsupials are mammals because they have hair and mammary glands.

Show question

Question

These mammals give birth to live young.

Show answer

Answer

Marsupials

Show question

Question

What is the difference between marsupials and eutherians?

Show answer

Answer

  • In eutherians, the mother invests a roughly equal amount of energy in rearing its young before birth via placentation and after birth via lactation. 

  • In marsupialsgestation is brief, and the placenta develops late into pregnancy. Lactation is extended and takes place in multiple stages, with the milk composition changing as the offspring grows (essentially performing the function of the eutherian placenta).

Show question

Question

Australia used to be connected to South America and Antarctica as part of ______.

Show answer

Answer

Gondwana

Show question

Question

Are rodents marsupials? Why or why not?

Show answer

Answer

No, rodents belong to a different evolutionary lineage. They are considered eutherians because their gestation and lactation periods are almost equal in length.

Show question

Question

What makes the female marsupial reproductive anatomy unique from other mammals?

Show answer

Answer

All female marsupials have a pair of lateral vaginae that each open into a common cavity called the urogenital sinus, which then empties into a short chamber called cloaca that connects to the intestinal tract. They also have two uteri.

Show question

Question

In most marsupial species, the developing young  are held in a maternal pouch called ____.

Show answer

Answer

marsupium

Show question

Question

Marsupials have a ___ gestation period than eutherians.

Show answer

Answer

shorter

Show question

Question

Marsupials have a ____ lactation period than eutherians.

Show answer

Answer

longer

Show question

Question

In Australia, there are cases where eutherians and marsupials seem to have undergone ______; that is, by occupying similar ecological niches, they have shared traits that evolved separately. 

Show answer

Answer

convergent evolution

Show question

60%

of the users don't pass the Marsupials quiz! Will you pass the quiz?

Start Quiz

Discover the right content for your subjects

No need to cheat if you have everything you need to succeed! Packed into one app!

Study Plan

Be perfectly prepared on time with an individual plan.

Quizzes

Test your knowledge with gamified quizzes.

Flashcards

Create and find flashcards in record time.

Notes

Create beautiful notes faster than ever before.

Study Sets

Have all your study materials in one place.

Documents

Upload unlimited documents and save them online.

Study Analytics

Identify your study strength and weaknesses.

Weekly Goals

Set individual study goals and earn points reaching them.

Smart Reminders

Stop procrastinating with our study reminders.

Rewards

Earn points, unlock badges and level up while studying.

Magic Marker

Create flashcards in notes completely automatically.

Smart Formatting

Create the most beautiful study materials using our templates.

Sign up to highlight and take notes. It’s 100% free.

Get FREE ACCESS to all of our study material, tailor-made!

Over 10 million students from across the world are already learning smarter.

Get Started for Free
Illustration