Remarkably, in history, we have see the continents move apart and come together,
and move apart and come together in different places around the world.
And during the Cenozoic time period when these large scale crusto processes and
mechanisms were in motion, they had a dramatic effect on what was going on in
terms of global evolutionary biology.
And so one of the mechanisms that was laid out by Darwin as a way to
generate new types of species was something called allopatric speciation.
And that is the idea that once you have some kind of a physical process,
like a mountain built, a new glacier forming,
volcanics that shut off land areas where you could have migration.
You have flooding and suddenly have a new ocean pathway that was formed.
Any kind of a physical barrier that could prevent the migration of organisms back
and forth would be a good way to have the gene pools,
via sexual reproduction isolated from each other.
And then generate a new group of organisms.
And so, this idea of allopatric speciation, geographic separation,
enhancing the ability to radiate new species, has been a really important
tenet, in looking at the, evolution of macro eukaryotic organisms.
So we've seen that played out extremely well in
terms of North and South America as one example.
So let me just go through the details of this South America's contextual stage.
And we'll see how the drama played out over the organisms between the two
different continents.
So with respect to South America,
now South American rifted from Africa in about the late Cretaceous, so
again this is a late Cretaceous going into Cenozoic ongoing process that took place.
And once that we had the separation from Africa and
South America physically, then we started seeing that marsupials and
placental herbivores migrated to South America.
And again, this all took place at the end of the Cretaceous.
And once that isolation continued and the ocean became larger,
the southern part of the Atlantic, then that isolation locked in and
the allopatric speciation kicked in.
And so, we saw this remarkably play out for South America.
So, the mammals were dominant then and remained on Africa.
And then the marsupials took over and
capitalized on the South American continent.
Remarkably, we saw all kinds of evolution of marsupials which ended
up looking a lot like the placental mammals that had remained back on Africa.
But they filled the same kind of ecosystem space, but
they were definitely not placental mammals, they were marsupials.
And some of the largest carnivores that we've had on the planet in the Cenozoic
time period were actually sabertoothed marsupials, and
we'll see that in just one moment.
So if we look at kind of an overlay of what some of these organisms look like
we'll see that we had a one for one counterpart between Africa and
South America.
And in terms of the wolf like organisms,
the placental wolf, there was a Tasmanian wolf.
Again, it was a marsupial, not a placental mammal.
A flying phalanger versus a flying squirrel.
We had an anteater develop that were both marsupial and placental.
And then we had, as an example, moles that were developed, that evolved that were
both either placental or marsupial, so we had this one for one exchange.
And we've seen this before when the same kind of ecosystem allows the radiation and
dominance of a different organism that looks somewhat
similar to what was there before.