Thanks to Brilliant for supporting  this episode of SciShow.

Go to Brilliant.org/SciShow to check  out all of their interactive courses. [ INTRO ♪ ] Ah, yes, marsupials. The endearingly oddball  pouched mammals you find in Austraila.

Well, that’s not entirely fair. There are a solid handful of  marsupials in South America, and just one genus in North America: the opossum. So how did this lone marsupial wind  up so far from all its relatives?

Well, as it turns out, it was North America that  was once the bustling hotspot for marsupials, long before Australia became the  place to be for mammals with a pouch. The fossil record tells us that marsupials  didn’t get their start in Australia. The oldest ones we know of are found elsewhere.

The oldest known ancestor of marsupials  is about 125 million years old, and was discovered in northeastern China in 2003. 110 million year old fossilized  marsupials have also been found in Canada, along with Montana and southwestern  Utah in the United States. And in 2009, researchers uncovered a fossilized   skull in limestone from the  Bighorn Basin in Wyoming, that looked an awful lot like a  marsupial we all know and love today. It turned out to be the fossil of an  ancient marsupial, known as a peradectid.

These are close relatives  of all modern-day opossums. By the way, even though we like to  drop the “o” here in North America, there is a scientific difference  between possums and opossums. One’s found in Australia, the  other in North and South America.

The discovery of this skull led  researchers to determine that peradectids arose in North America around the  time the dinosaurs went extinct, about 65 million years ago. Ancient marsupials, including peradectids, are thought to have moved freely  between North and South America. Around this time, however, North  and South America separated, and the fate of the marsupials  played out differently on each.   North America’s original  marsupials actually went extinct.

But during the period that South America  was isolated from other continents, its marsupials continued to diversify. About 3 million years ago, North and South America decided  to get the band back together via the Isthmus of Panama, and a bunch of different animals suddenly  had a whole new continent to explore. That included North America’s two new, and to this day only, marsupials.  One is the Virginia opossum, the only marsupial that is  found north of Mexico today.

The other is the Southern opossum, found  in Mexico and parts of South America. So North America’s marsupials  ruled, died out, and rose again. At least in the form of the Virginia  opossum so well known to so many trash bins.

And what about Australia? Researchers believe that marsupials  made their way to Australia when South America, Australia and Antarctica were all connected as one landmass. But North America, along with Asia, is actually where they got their start!

Researchers are still debating why the early  home of marsupials is now host to only two. Some have hypothesized that North American  marsupials were outcompeted by placental mammals, where in South America and Australia there  might not have been as much competition. Other researchers disagree with  the competition hypothesis, saying marsupials and placentals  reigned at different times.

Whatever the case, we now have one  more reason to love the opossum. Not only are they adorable when they’re eating, they’re also helping us to trace the  family history of all marsupials. We’re always learning new  things like this in science.

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