Wednesday, October 11th is National Fossil Day and I’m excited to announce we’ll be celebrating with another Eons livestream!
This year, we'll be playing a game called "Wheel of Deep Time" and I wish I could tell you all about it but our producers have refused to share a single detail with any of the hosts.
So it sounds like we’ll be learning the game alongside you all!
Join me, Michelle, Blake, and the newest member of our team for an hour of fun - right here on YouTube on Wednesday, October 11th.
Around 93 million years ago, in what's now New Jersey, an ancient ant named Kyromyrma neffi made its way across a forest floor, hunting for prey to bring back to its underground nest.
Suddenly, it found itself caught in a blob of sticky resin released from the branch of a conifer tree above.
What was terrible luck for this ant turned out to be incredible luck for paleontologists, who, millions of years later, found it almost perfectly preserved in amber.
Kyromyrma is the oldest known ant that belongs to a modern subfamily that’s still around, an ancient relative of ants that rule the world today.
But in Kyromyrma’s day, ants weren’t especially common or diverse compared to other insects.
They make up less than 1% of insects found in amber from the Cretaceous Period, and they only lived on the ground and nested in the soil of humid forests.
They weren’t found in drier and more open environments…yet.
But in the Cenozoic era, they make up a staggering 40% of insects in amber, and today they number in the quadrillions.
They’re found in almost every habitat on Earth - from tree canopies to open grasslands to arid deserts.
So how did they do it?
How did ants take over the world?
Well, it looks like ants didn’t achieve world domination all by themselves… They may have just been riding the wave of a totally different type of evolutionary explosion.
The story of the rise of ants began around 140 million years ago, sometime around the Early Cretaceous, when an ancient species of wasp underwent a pretty momentous change.
It lost its permanent wings, kept its predatory lifestyle, and adapted to life on and under the forest floor.
This was the origin of the family Formicidae, aka the ants.
Yup, that's right - ants are essentially a family of flightless wasps.
And in the time since their origin in the Mesozoic Era, they’ve radiated into more than 14,000 known species across 16 living and 5 extinct subfamilies.
There’s probably more species of them around today than all mammals and birds combined.
And in some environments, like the Amazon rainforest, they likely outweigh those vertebrates by total biomass, too.
So, what turned them from the ecological side-characters that they’d been for tens of millions of years into one of the most numerous and diverse animal groups of all time?
Figuring out the mystery of their rise to main character status has been tricky.
For a long time we just didn't have enough Cretaceous ant fossils to understand much about their early days.
Plus, their incredible modern diversity meant that we struggled to even untangle how living groups are related to one another.
But in 2005, two leading ant experts, EO Wilson and Bert Hölldobler, proposed the first overarching explanation for how ants took over: the Dynastic Succession Hypothesis.
Such a grandiose title, I love it!
They predicted that the key to ants moving beyond the forest floor was actually the rise of another major group, one that began revolutionizing terrestrial ecosystems around the world in the Cretaceous: flowering plants, aka angiosperms.
Much like ants, angiosperms are another extremely diverse, major feature of nearly all terrestrial habitats today.
They represent around 90% of all living plant species.
But they too only began their rise in the Cretaceous and established their full dominance in the Cenozoic.
So, what if ants weren’t just diversifying alongside angiosperms during this time, but directly because of them?
The following year, in 2006, we found the first good evidence in favor of this hypothesis.
A team of researchers produced the first large-scale family tree of modern ants based on genetic data.
It included DNA from 149 species, covering almost every subfamily of living ants.
Using a molecular clock analysis, they calculated when lineages diverged from one another, which let them uncover patterns in the group's evolutionary history.
This revealed that a wave of diversification did take place across the family tree between the late Cretaceous period and the early Eocene epoch, closely tracking the rise of angiosperms.
The overall pattern was clear: after flowering plants took off, ant lineages all over the world diversified in their wake.
But what was driving this pattern?
Well, the more diverse a group is, the more data you need to collect before you can start to really dig into the details of that group’s evolution.
And both ants and angiosperms are, well, just ridiculously diverse.
But in two papers in 2018 and 2023, researchers were finally able to pull together enough data to uncover some major pieces of the puzzle.
They used an expanded family tree of over 1400 ant species, combining genetic and fossil data with information on their key traits, climate and habitat preferences, and lifestyles.
All that data allowed them to reconstruct ants’ evolutionary history by working backwards from today’s diversity, tracing the history of particular traits and lifestyles over time using a technique called ancestral state reconstruction.
And they combined that with similar data on the evolution of flowering plants to establish the key sequence of events.
Starting in the Cretaceous, some ant lineages began venturing upwards from the forest floor to forage in the new, more complex tree canopies of the increasingly angiosperm-dominated forests.
The gradual takeover of these forests by flowering plants had bumped up the moisture levels at greater heights.
This made the forest canopy more hospitable to ants, as well as the smaller arthropods that they hunted.
Multiple ant lineages began incorporating plant-based food sources into their diets too, transitioning from strict carnivory to omnivory and eventually to herbivory in some groups.
And many plants responded by independently developing specialized structures that kept the ants hanging around.
This probably happened because the ants helped ward off more destructive pests and herbivores.
These structures took the form of what are called extrafloral nectaries - little sugar fountains seen in over 4000 modern plant species, which they offer to ants in exchange for protection.
Over time, some lineages that foraged in the trees began to move their entire nests from the ground up into the canopy itself.
The first lineages to make the switch to arboreal nesting did so right as the Cretaceous gave way to the Paleogene Period.
And as ants moved into entirely new niches within forests, thanks to the explosion of angiosperms, competition between coexisting ant species was reduced.
This let ants rapidly diversify and increase in abundance.
So many ants were now running around the forests, and spending time on and around angiosperms, that the plants developed another way to make the most of the situation, using this new abundance of ants to help disperse their seeds.
They developed elaiosomes, small fleshy structures attached to their seeds.
These have convergently evolved over and over again in flowering plants from the end of the Cretaceous onwards, as more and more plants found success using them to attract and recruit ants to carry their seeds far and wide.
But this partnership didn’t stop there.
Just as angiosperms helped ants expand to new niches within forests, they also allowed ants to expand to niches beyond forests for the first time, too.
Because as the Cretaceous gave way to the Paleogene, angiosperms spread and established entirely new ecosystems in much drier and more open areas.
They formed the first grasslands, which spread around the world in the Paleogene and Neogene Periods.
Some angiosperms also adapted to thrive even in the driest of environments, like deserts.
And from sometime in the late Paleogene onwards, many ant lineages on different continents independently followed them out of the forests and diversified in those new habitats.
Thanks to the habitat and food provided by the angiosperms, the ants adapted to thrive in environments they might never have been able to spread to alone.
So, while it may feel like we live in a world full of ants today, that's only because they themselves are living in a world full of angiosperms.
And without the flower power that fueled their rise and spread, they might have forever remained as obscure, uncommon predators of the forest floor.
But, being among nature’s most impressive ecological opportunists, they hitched their evolutionary fate to another absurdly successful group, and forged a relationship that would change them, and the world, forever.
Rocks are cool.
This is one thing I think all of us can agree on, at least all of us over here at Eons.
Well, our friends over at SciShow also think rocks are cool and have a very exciting, rock-related announcement in the works that they will tell you all about on October 2nd.
So if you like rocks, and we know that you do, head on over to youtube.com/scishow on October 2nd for something that totally ….
Rocks.
We’d like to thank Dr. Corrie Moreau, Moser Endowed Professor and Curator at Cornell University who lent her expertise to this episode.
Also thanks to this month’s import-ANT Eontologists!
Jake Hart, Raphael Haase, Annie & Eric Higgins, John Davison Ng, Melanie Lam Carnevale, Addie, and Tony Dai.
Become an Eonite at patreon.com/eons to get fun perks like submitting a joke for me to read!
Like this one from Claire.
Why didn't my mom want me talking to modern dinosaurs?
She didn't want me using fowl language.
Fowl language?
Like a chicken?
Because birds are modern dinosaurs?
And as always thanks for joining me in the Adam Lowe studio.
Subscribe at youtube.com/eons for more journeys in deep time.
And in some environments, like the Amazon rainforest, they likely outweigh those vertebrates by total biomass, too.
Eek!
So gross...
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