Dear Bunjicus Wunjicus, what is the great American biotic interchange?

okay so, for the vast vast vast VAST majority of their time in existence as continents, North and South America have been completely separate continents, with oceans in between them.

135 mya (million years ago):

60 mya:

once they separated from Laurasia and Gondwana respectively and became their own thing after the Big Kablooie (66mya), they both started to evolve their own completely unique ecosystems with their own forms of life!

North America was a bonanza for big cats, proboscideans, bears, and canines:

<art src: Joe Venus>

while South America went big on giant sloths, terror birds, marsupials, and armadillos that could tow your car:

<art src: Gabriel Ugueto>

and so they remained, two houses alike in dignity, but rarely interacting except for swapping stormtossed refugees once in a while as they very slooooowly drifted towards each other.

and then, 2.7 mya, the two drifting continents uplifted the seafloor between them like a snowdrift in between two oncoming plows and made much of Central America and Panama.

AND EVERYTHING CHANGED WHEN PANAMA ATTACKED

and WHOOOOPS.

suddenly, the biota of both continents had freedom of movement into a totally new environment. terror birds pushed north into Central and Southern North America, only to be pushed back by incoming waves of smilodon, jaguars, and pumas.

<src: Life On Our Planet>

canines and proboscideans and bears and rabbits and predators of all shapes and sizes came roaring south into the body of South America, wreaking environmental change in their wake, while fleets of possums, armadillos, and giant sloths trekked north to find some new niches of their own.

when the dust had settled, South America was VERY different from how it had first looked, with many native predators supplanted by carnivorans and many small to medium herbivores supplanted by northern species. the terror birds were gone, ending the last legacy of the dominant predatory theropods.

<src: Mauricia Anton>

North America had picked up some new additions of its own, some that lasted (armadillos, possums) and some that didn't.

<src: Peter Schouten>

and we call this kerfuffle the Great American Biotic Interchange, because it sounds better than ECOLOGICAL WARZONE: ESCAPE FROM BRAZIL

(if you're a scientist, anyway)

<src: Guillermo Torres Carreño>