Monday, March 2, 2015


Marsupials are a subclass of mammal that have managed to evolve without a placenta. Marsupials actually birth their young at such an early stage as to still consider them embryos when compared with placentals; this is possible because the young marsupial is birthed into a pouch where it's able to avoid danger. As you can imagine this isn't as efficient as placental mammals where the young are born much stronger; This is because they've been protected and given a constant supply of nutrition up until birth. Young marsupials actually have to crawl up the pouch and find a tit to get the nutrients they need in order to make it to the development of a newly born placental mammal.

Marsupials had evolved and been living in Gondwana after the supercontinent Pangea split up. Gondwana was composed of what is now Africa, Australia, South America, Madagascar, New Zealand, Arabia, India and Antarctica. 

You might be asking yourself why Australia is the only continent known for marsupials if Gondwana consisted of many now known continents? Well, Australia was the prime location for the development of marsupials because it lacked many large predators and placental mammals. With nothing to really outcompete the existing marsupials that had been living in that area after the split from Gondwana: The marsupials flourished with adaptive radiation.   

What's interesting about this adaptive radiation is that marsupials evolved in many of the same ways that our placental mammals have in the America's and elsewhere. This similar evolution is known as convergent evolution, and I find it truly amazing that despite being in completely different locations; we see many of the same morphologies. 

The image above shows some examples of this convergent evolution. When I stop to think about how this convergent evolution took place, I find myself asking what exactly is it about certain terrains and our food chain that causes these morphologies to be so similar?  Perhaps a lot of this adaptive radiation occurred with the common ancestor to both subclasses of mammals, and that these morphologies just kept getting passed down up to Australia's separation and then elaborated on when the separation occurred? If anyone has any other ideas or wants to add their thoughts then please do so! 

Post by Mitchel Logan (B) 


  1. Cool post! Evolution was one of my favorite classes and we talked about this in that class. I think these convergent evolutions happen because these adaptations that these sets of creatures have are just very good adaptations. In Australia and other places these organisms have been adapting for millions of years, and these same adaptations work regardless of where the creatures are based out of. I find it interesting that there are so many Australian creatures that are so similar to non-australian ones.

    -Madison Boone

  2. This is a very interesting post! For one of your questions in the last paragraph asking about what causes these morphologies to be so similar, in my opinion, living condition including habitat, food chains, predators,.. is definitely one of the causes. In convergent evolution, organisms are not closely related or not monophyletic independently evolve similar straits to their own environments. One of the examples that I remember from my anthropology class is that in tetrapods (all mammals, birds, reptiles, and amphibians), during fetal development, 4 limbs are being formed followed by the development of 5 branches at the limb ends. However, we can obviously point out the differences between humans' hands versus cats' paws and birds' wings. The formation of these changes occur as their adaption to the surrounding environments in order to increase their abilities to compete, survive and reproduce. That's why we can find creatures, organisms that are very geographically distinctive with very similar morphologies. That's just my understanding. Correct me if I'm wrong. Great job, Mitchel!
    -Posted by Phi Duong

  3. Convergent evolution is really cool. It is especially fun to think about biologically - how the mastermind of evolution finds the best fit time and time again. One of my favorite examples of this phenomena is the evolution of wings in birds, insects, dinosaurs, etc... Wings work - and evolution knows it. Marsupials are really awesome creatures, and I enjoyed reading your post about this topic! Great work!

    -Michael Salhany