Hey, I have an announcement!

I wrote a book!

It’s called “Tales of the Prehistoric World.” It features over 60 stories of  paleontological discoveries with   illustrations by Becky Thorns.

It’s rated for  ages 8 - 10 but also anyone young at heart.

You can order it through your local  bookseller or wherever else books are sold.

On December 6th, 1834, a young Charles Darwin was   visiting San Pedro island off  the coast of southern Chile.

It was the latest stop on his long voyage  around the world – the one where he began   to develop his ideas about the origin of species.

On the island, he noticed a tiny  fox-like creature - a canid of some   sort - sitting on the rocks, completely  absorbed in watching the men working.

The species was unknown to western science and   different from the other canids  Darwin had seen in South America.

So, as the group’s naturalist, he decided to  collect a specimen to send back to England.

The fox was so distracted that  he was able to sneak up behind   it and knock it on the head with his  geology hammer – not cool, Darwin.

He’d later describe that poor fox as “...more  curious or more scientific, but less wise,   than the generality of his brethren.” In  other words, curiosity killed the canid.

Today, we call this species ‘Darwin’s Fox’,  and it’s one of ten very different canid   species that call South America home - the most  diverse canid community found anywhere on Earth.

But while Darwin collected the fox for science,  he’d never know the real scientific story it,   and those other canids, represented –  though he probably would have loved it.

Because, while South America  today has the most canid species,   until relatively recently it had none.

And the origin of these species?

Well,   just like the finches of the Galapagos  that would inspire him later on,   it turns out that South America’s canids are the  result of an adaptive evolutionary radiation… One driven by great migrations,   insurmountable geological barriers,  and new ecological opportunities.

These canids were, in a sense,  the finches that Darwin missed.

It would take nearly two centuries of  further research, and development of   entirely new fields of science for us to finally  figure out how South America got its canids.

And the reason that it was so mysterious for so   long is because the whole  situation is kind of odd.

See, despite South America having the  greatest canid diversity of any continent,   it was clear that they must have  only arrived fairly recently.

After all, North America - not South  - was the cradle of canid evolution.

That’s where the fossil record shows  canids originated and evolved for tens of   millions of years, as far back as the late  Eocene epoch, around 40 million years ago.

Some groups rose and fell in North America, and,  in the late Miocene epoch, around 6 million years   ago, some groups migrated into Eurasia, giving  rise to all modern Eurasian and African canids.

But canid migration into South America could  only have become possible more recently,   within just the last 3 to 4 million years,   following the formation of the isthmus  of Panama in the late Pliocene epoch.

This land bridge enabled an exchange of  many species between the two continents   in a series of events called the  Great American Biotic Interchange.

And for a long time, biologists  have been trying to figure out   why the canids of South America are so  diverse when they only arrived recently.

Did they diversify in North America  and migrate south separately?

Or did they suddenly radiate  from a single common ancestor   into radically different  species once they arrived?

Well, the fossil record of canids  in South America is pretty patchy,   so it can’t give us many clear  answers to those questions.

But if you can't trace a story  forward in time from ancient evidence,   then you have to trace it back  in time from modern evidence.

And today, we can do this by digging  into and comparing the genomes of   living species to reconstruct  their evolutionary history.

It’s an approach that, I think is fair  to say, would have blown Darwin’s mind.

See, he knew nothing about DNA, and, even today,   genomes are sometimes mistakenly just thought of  as molecular recipe books for building organisms.

But they’re also historical records,  as the pattern of mutations and genetic   diversity they contain reflect an  organism's evolutionary history… From the migrations of their ancestors, to  the population expansions and bottlenecks   they underwent, to the selective  pressures they faced, and more.

And with enough genomic data, sufficient computing  power, and the right algorithms, it’s now possible   to reconstruct the history of populations far back  into deep time, even with few fossils available.

So in 2022, scientists published the results of a   study applying this approach to solve  the mystery of South America’s canids.

Using a mix of new and previously  sequenced genomes, they compared   all ten living species from across the continent.

And the family tree they built showed that,   despite their many physical  and ecological differences,   all ten descended from a single common ancestor  that lived just 3.9 to 3.5 million years ago.

And, based on patterns of genetic  diversity, they estimated that this   ancestral population was fairly small, with  only around 11,600 breeding individuals.

This suggests that all South American canids  stem from a single dispersal event of one   ancestral species from North America  over the developing isthmus of Panama.

This single species gave rise to the most diverse  canid community on Earth in just a few million   years - a staggeringly fast and large-scale  radiation for a group of mammalian carnivores.

But that ancient canid lineage would have first  been faced with a major geological barrier.

See, the Andes Mountains had reached their  present-day elevation by 6 million years   ago and stretched the length of the continent.

And using a statistical approach  called biogeographic modeling,   the researchers estimated that, while canids  today are found on both the eastern and   western sides of the mountains, the ancestral  species actually only entered via the east.

This suggests that they came from Central America   to the east side of South America by way  of a natural corridor of grassy woodland.

We know from fossil evidence that  many other North American mammal   groups also used this route during  the Great American Biotic Interchange,   so it seems like the Andes were a  major barrier to western dispersal.

And the researchers found the genetic signal of  a massive increase in population size once those   early canids arrived - a result of the enormous  ecological opportunities they found there.

They faced very little direct competition in  their new environment, as the few South American   carnivores, like the marsupials and terror  birds, played very different ecological roles.

So the canids were unlike anything else on  the continent, which allowed them to thrive   and radiate into a range of unoccupied niches.

Based on their genomic analysis, the researchers   also found that the first lineage to branch  off was a group containing the bush dog and   maned wolf, which, despite their obvious  differences, are actually sister taxa.

Much like the finches of the Galapagos,  the distinctiveness of these canids from   each other is the result of wildly  different niches that they fill.

The maned wolf became adapted for  navigating through tall grasslands   and developed an omnivorous  diet including lots of fruit,   while the bush dog specialized as a  small, but powerful, hypercarnivore.

Despite having a common ancestor just  3.1 million years ago - around half the   divergence time of us and chimps  - these two sister canids adapted   so differently to their environment that  they lost almost all family resemblance.

Tracking the radiation of the rest of  the canids, the researchers found they   continued to diversify on the eastern side  of the Andes as they expanded farther south.

This gave rise to a second group that includes  the crab-eating fox and short eared dog.

Then, starting around 1.4 million years ago,   the 6 fox-like species in the  genus Lycalopex began to diverge.

And by 1 million years ago, a lineage of  this group finally made it west of the Andes.

The researchers’ modeling suggested they went  down and around the mountains, a journey of   thousands of kilometers along the southern edge  of the range.

Talk about taking the scenic route!

And this probably happened during  dry periods of the Pleistocene epoch   that drove the expansion of more grassy  woodland corridors that they could cross.

This lineage gave rise to three species  on the western side of the range,   including our friend Darwin’s fox,  in a final burst of speciation.

When he encountered that fox on San Pedro  Island, Darwin had no idea that it, too,   had only recently made it there as part of an  epic, trans-continental journey of its own.

And he never found out that this  radiation of ten canids from one   small ancestral population was actually  an unusually powerful example of the   evolutionary process he would later  propose in The Origin of Species… The process by which, in his own  words, '...from so simple a beginning,   endless forms most beautiful and most  wonderful have been, and are being, evolved.” Don't forget!

Our 2023 calendar  featuring 14 reconstructions of   some of our favorite main characters of  paleontology from classic Eons episodes,   are available now at ComplexlyCalendars.com.

And thanks to this month’s foxy Eontologists!

Jacksy Weiss, Colton, Melanie Lam Carnevale,   Chase Archambault, Annie & Eric Higgins,  John Davison Ng, and Jake Hart.

By becoming an Eonite at patreon.com/eons you’ll  get fun perks - like submitting a joke for us   to read.

Here’s one from Andrew M. Did you hear about the species of   skunk that evolved to lose their  stink gland?

They went ex-stinked!

That was actually...that, that was  good, that was good, good job.

And as always thank you for joining  me in the Adam Lowe studio.

Subscribe   at youtube.com/eons for more prehistoric stories.

This is so... We'll try one with [the  hammer], we'll try one without!

The fox was so distracted that he  was able to sneak up behind it and   knock it on the head with his geology  hammer – not cool, Darwin, not cool.

It's so bad.

It's so bad!

Ohhhhhhh... it's so bad!

Ok, one without.