If you don’t know a lot about kangaroos, you might be wondering whether a kangaroo is a rodent. Let us answer this question so that you understand the difference between a marsupial (kangaroo) and a rodent.
A kangaroo is a marsupial and not a rodent.
While both of these animal species are considered mammals, there are vast differences between them. Like all mammals, both marsupials and rodents are covered with fur and have mammary glands in order to feed their young. However, that is where the similarities end.
While rodents are considered placental mammals, marsupials are not. On top of that, there are also monotremes which are egg-laying mammals. These include the Australian platypus and two different species of echidna.
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What Is A Marsupial?
Marsupials differ from most other mammals because the embryonic development happens in the animal’s pouch rather than within a placenta in the uterus. All female marsupials have a pouch and this is where the tiny baby will live for it’s first few months of life to develop and grow.
When tiny baby kangaroos are born, they are totally blind and completely without hair, much like other mammalian embryos. Baby kangaroos, like other marsupials, are born after around eight days of fertilization.
At this stage, the baby is only about the size of a jelly bean. Being totally blind and not yet fully developed, it somehow finds its way into the pouch of its mother. Once there, it attaches itself to one of four teats.
At this time of its life cycle, the tiny kangaroo is not even strong enough to suckle. That’s why the mother kangaroo will instinctively pump the milk that the baby needs straight into its mouth. The baby then continues to grow and develop and it’s a further 6 months or so before it is large enough to appear out of the pouch.
Around two thirds of all living marsupials live in Australia and New Guinea while the other third can be found in South America. There is even one marsupial, the Virginia opossum, that lives in North America.
What Is A Rodent?
Like marsupials, rodents are also mammals. However, their babies are developed within a placenta in the uterus, very much like human babies. Rodents belong to the order Rodentia of which there are over 2000 species.
What differentiates rodents from other mammals is the presence of chisel-like incisors both in the upper and lower jaw. Animals regarded as rodents include rats, mice, beavers, porcupines, gophers, squirrels, chinchillas and mole-rats.
Most rodents are fairly small in size except for the capybara species. The capybara is a very large cavy rodent and is native to South America. This particular species can weigh as much as 145 pounds (66 kg).
Major Differences Between Marsupials And Rodents
Scientists believe that placental mammals such as rodents evolved after the evolution of marsupials. Here are some of the major differences between marsupials and rodents:
- Rodent embryos undergo their full development in the mother’s placenta and within the uterus before they are born.
- Marsupial embryos are born before they’ve finished developing and continue to develop within the mother’s pouch.
- Rodents can be found all over the world.
- Marsupials are only found in Australia, New Guinea, North and South America.
- Marsupials generally have their fertilized eggs surrounded by amnion and chorion membranes while rodents do not.
- Rodents have a pair of chisel-like incisors both on their upper mazilla and lower mandible.
- Most female marsupials have a pouch that protects their young while rodents do not. This feature is commonly referred to as marsupium.
- Female marsupials actually have 2 uteruses and 2 vaginas. These join up to form a third vagina and the birth canal.
- Marsupials also have an extra pubic bone known as the epipubic bone. This helps to support the pouch.
History Of The Evolution Of Marsupials
It’s believed that the ancestors of marsupials go way back to the dinosaur days and many of these lived in South America which was attached to Antarctica at the time. Previous to this, Australia was also connected to this huge land mass known as Gondwana.
During this time, there were no placental mammals but a huge range of large marsupials such as bear-like marsupials and sabre-toothed marsupials.
Australia separated from Antarctica around 80 million years ago and it’s understood that all the marsupials remained on the land mass that is now South America.
Similarly, it’s believed that marsupials only made their way back to Australia around 55 million years ago by crossing both Antarctica and the Southern ocean. While research is still a bit sketchy, it is believed that all the marsupials now living in Australia are descendants from those first marsupials that came across Antarctica.
Of course, as we now know, South America and Antarctica later also separated and it turned out that all the remaining marsupials ended up in South America. In fact, even today, around a third of the marsupial species live in South America. These include the yapok, the woolly opossum and the gray four-eyed opossum.
Today, the largest living marsupial is the red kangaroo that lives only in Australia. On the other hand, the largest extinct marsupial is the Diprotodon that is believed to be an ancestor of the Australian wombat.
Final Thoughts
If you ever wondered whether a kangaroo is a rodent, you should now know the definitive answer to this question. In fact, kangaroos are marsupials and not rodents. But, both do belong to the larger family of mammals.
The main differences between marsupials and rodents is how the young develop. While rodent embryos develop fully in the placenta of the uterus, marsupial embryos are born before they’re fully developed and spend a few months inside the mother’s pouch to complete their growth and development.
It’s also interesting to note that not all marsupials actually have a pouch. One species, the short-tailed opossum, doesn’t have a pouch at all. Rather, the female of the species has teats that retract into her body to feed the developing embryo.