How Did Marsupials Evolve?

In Australasia, there exists a sort of animal that’s markedly different from those found anywhere else in the world.The female of this sort of mammal has its mammary glands contained within a special pouch, in which its young grows and subsists on mother’s milk until it’s ready to leave.But exactly how did this weird arrangement evolve, and why is it so unique to Australia and New Zealand?Let’s take a look and see if we can shed some light on the matter.

Ancient beginnings

Marsupials are thought to have diverged from the more commonplace placental mammals around ninety million years ago.The likely point of this divergence is probably North America, from where the animals spread to South America and the Pacific Rim.One should remember that at this time, the sea levels would have been markedly different, and it might have been possible for land animals to walk across stretches of land that are now entirely underwater.

By the late cretaceous period (near the time that the dinosaurs were wiped out by a massive asteroid impact), Marsupials had begun to move into Australia via Antarctica.Australia, at this point was attached to Antarctica via Tasmania, which had yet to break apart and form its own island.There were no polar ice-caps, and carbon-dioxide levels were around four times as high as they are currently.This made it relatively straightforward for even small animals to survive the trip from South America to Australia.

Expert opinion is split as to exactly when this migration might have taken place.One theory holds that it might have been possible even after the two landmasses had become separate, through a process called ‘rafting’.This is as it sounds – a mass of vegetation, or some similar floating material, breaks off from one landmass and literally floats to land on another.Since the ancestors of marsupials were smaller than their modern descendants (which is part of what allowed them to shelter from the extinction even that wiped out the dinosaurs), they are better able to survive a short trip across the ocean via rafting.While this might sound like an implausible theory, it’s one with several well-established precedents.

What does a pouch look like?

In some marsupials, the pouch opens forwards and up.In others, it opens backwards and down.This is necessarily so – if a kangaroos pouch opened in the same way as a koalas, then the young would fall out.Similarly, if the pouch of a marsupial mole opened forwards, then the pouch would fill with dirt as the animal dug, and the young would suffocate.While koalas have backward-facing pouches, they don’t suffer from the problem of their young falling out; they have a strong sphincter muscle around the opening of the pouch which prevents this.

Why are Marsupials so much more abundant in Australia?

If early marsupials had to travel so far in order to get to Australia, then the question is:why are there no marsupials left along the way, and so many in Australia?The simple answer is that there still are many species of marsupial in South America, but they’re still much smaller than the ones you find in Australia.This is probably because there aren’t enough predators in Australia to control the upward spread of marsupials.Thus, those early marsupials were able to evolve to become bigger and bigger, until we arrive at the modern-day kangaroo.

What are the main types of marsupial?

Marsupials come in hundreds of different forms – but of these, the most famous is probably the kangaroo.These creatures evolved from tree-dwellers, whose feet would have been suited to a vertical lifestyle.When they finally came down onto the forest floor, they adapted a hopping technique for getting around.This technique has since served them well – they’ve evolved massive, powerful ligaments which allow them to get around with barely any exertion at all.Koalas, on the other hand, went down an entirely different path – they live almost their entire lives up in trees.

Where can I see a marsupial?

If you’d like to catch a glimpse of a marsupial in its natural habitat, then the only way to do so is to venture to Australia.It’s here that you’ll find both kangaroos and koalas – and doing so isn’t difficult, as they’re abundant.Moving to Australia or nearby New Zealand requires navigating the respective points-based immigration systems of either country.Fortunately, Australian or New Zealand Visas for UK citizens are relatively easy to come by.