Eons

Over 66 million years ago, in a Late Cretaceous forest, the ground rumbled as a giant approached.

A titanosaur measuring nearly 40 meters long and weighing around 70 tons came crashing through the vegetation.

The lumbering megaherbivore shattered branches and trunks, trampled ferns and flowers, and broke open gaps in the canopy, causing bright beams of sunlight to stream through to the forest floor.

For the poor plants of this ancient forest, this was just another chaotic day in the Mesozoic.

These ancient ecosystems werent just ruled by giant dinosaurs, they were also constantly being shaped, or engineered by them, too.

Enormous dinosaurs were so widespread and so common for so long that they became a force of nature in their own right, having huge impacts on the evolution of the species around them.

And after around 160 million years of giant herbivorous dinosaurs crashing through these forests, the plants that lived there had adapted to cope.

Because of the regular disturbance, ancient flowering plants, or angiosperms, mostly evolved to play the reproductive odds - producing lots of small seeds with little investment in each one.

But when those giant dinosaurs suddenly disappeared during the K-Pg mass extinction, the ecological dynamics of planet Earth were altered forever in ways that were still feeling the effects of today.

And it seems that one of the most surprising effects of the cascade of changes that played out in the wake of their extinction may have been the evolution of a new world that was absolutely full of fruit.

And with a lot of fruit, came a lot of fruit eaters.

Now, its hard to imagine a world without fruit, but when you think about it, fruits very existence iskinda bizarre.

Fruit is the physical embodiment of an ancient co-evolutionary dance between plants and animals that stretches far into the deep past A colorful, juicy token of friendship emerging from a symbiotic relationship at least a hundred million years in the making.

See, plants spend extra energy and resources to develop big seeds with nutritious and delicious coatings to attract fruit eaters.

And those fruit eaters, in turn, pay the plant back by dispersing the seeds far and wide.

Fruit, then, is a strategy, and it has been so successful in our modern world that scientists estimate that in tropical forests today, up to 94% of woody plants produce some kind of fleshy fruit.

And this works so well because most of the animals in those forests have evolved to take part in the relationship, becoming at least partly fruit-eating, or frugivorous.

A win-win, right?

Well, like all evolutionary strategies, producing fruit only pays off when the ecological circumstances are just right.

And until fairly recently in our planet's history, in geological terms, the world simply wasnt ready for fruit.

Starting in the mid-1980s, researchers hypothesized that the big dinosaurs of the Mesozoic Era - the largest megaherbivores to ever walk the earth - acted as powerful ecosystem engineers, defining the evolution of the plant life around them.

These researchers argued that the fossil record shows that the reproductive strategy of early flowering plants was a response to the chaotic environment of those constantly-disturbed forests.

The plants survival strategy was to produce as many offspring as possible in the hopes that at least some found the right opportunity to thrive, even if most didn't.

This is what ecologists call r-selection. And in the case of flowering plants, it meant that seed sizes were often small and fruit was rare.

But after those dinosaurs suddenly went extinct around 66 million years ago, the reproductive calculus appears to have shifted.

As forests recovered in the Paleocene, they grew back much denser - finally freed from the persistent disturbance of giant herbivorous dinosaurs.

In these new, more stable forests, the hypothesis goes angiosperms shifted from r-selection to k-selection.

Which meant that their strategy suddenly became one of increased investment, with a decrease in overall quantity.

K-selection is usually something we see in more stable environments.

In these ecological conditions, its better to produce fewer, larger seeds, and invest more into each one.

And in the 2000s, other researchers built on this idea, arguing that these denser, darker forests of the Paleocene would have also created more competition for light among the plants See, based on data of carbon isotopes from fossil leaves, scientists have estimated that the understory of the more closed-canopy Paleocene forests received 19% less light than those more open forests of the Cretaceous.

This would have further selected for the evolution of larger seed sizes with bigger energy reserves in the Paleocene.

That strategy gave the next generation an early boost once they sprouted and helped them grow taller to better compete for light.

And with bigger seeds came more fleshy parts coating them, which attracted small- to medium-sized animal dispersers.

While some mammals and birds were growing rapidly in size during the Paleocene, radiating to fill niches left open by the demise of the dinosaurs, they were still pretty puny compared to their reptilian predecessors.

And, in some ways, they would never fully replace the dinosaur megafauna of the Mesozoic. Nothing even close to the scale of a giant sauropod would ever be seen again on land.

So, in the millions of years following the extinction event, mammals and birds were big enough to effectively disperse the ever-larger seeds of angiosperms.

But they were also still small enough to leave the dense Paleocene forests relatively undisturbed.

All the necessary conditions were now in place.

Earth was finally getting fruity.

And by about 55 to 50 million years ago in the Eocene, the world reached peak fruit.

The extensive tropical forests of the Eocene that stretched as far north as the Arctic supported the greatest diversity of seed sizes, fruit sizes, and fruit types in the planets entire history.

This, in turn, created entirely new niches for new and bigger fruit-eaters to thrive in if they could adapt to rely on these resources.

The earliest fruit-eating seed dispersers included birds and multituberculates - a now-extinct group of rodent-like mammals ranging in size from mice to beavers.

And over the next several million years, they were joined by more and more bird and mammal lineages that became increasingly reliant on the new abundance of fruit.

Like true rodents, fruit-eating bats, and eventually, us primates.

The story of primate evolution ever since has been deeply intertwined with fruit - its a topic weve covered before on Eons.

But that relationship may have first become cemented in the dark forests of the Eocene over 50 million years ago.

Back then, forests heavy with big and fleshy fruits were likely where our fruit-eating early primate relatives bounded from tree to tree, and from treat to treat.

Without the cascade of events that led from the extinction of giant dinosaurs to the development of these new fruity habitats and resources, we primates might never have had a chance to diversify, and you and I would never have evolved.

Now, it can be pretty hard to track exactly how all this played out, between the lumbering ecosystem engineers, the forest understory light levels, angiosperm seed sizes, and the co-evolution of dispersers.

There were a lot of things going on and the fossil record alone can only give you so much information.

So in 2025, researchers created a mathematical model to reconstruct the ecological dynamics of these long-term interactions as they played out over geologic time.

Their model was able to explain another phase in the relationship - a reduction in average seed size towards the end of the Eocene around 33 million years ago, down significantly from its peak earlier on.

This happened as some terrestrial mammals finally got big enough to put the mega back in megaherbivore like the enormous brontotheres, appropriately nicknamed thunder beasts.

The effects that this new wave of megaherbivores had on forest structure finally began to mirror the ecological engineering of the giant dinosaurs, albeit on a smaller scale.

And the model also offered two potential predictions about how these dynamics may be playing out today, leading to two possible scenarios for the future of fruit.

On the one hand, in recent times, ecosystems have been hemorrhaging big mammals, starting with the Pleistocene megafaunal extinction that began about 50,000 years ago and continues today.

In South America for example, the average size of medium-to-large sized animals has dropped from 834 kg to just 81 kg, through the extinction of megafauna like giant ground sloths and glyptodonts.

Similar patterns have played out around the world, mirroring the global loss of giant herbivorous dinosaurs at the end of the Cretaceous.

And the researchers model suggests that, over millions of years, this will lead to forests developing to be denser and darker once more.

And that could potentially drive seed sizes and fruit diversity back up towards their early Eocene peak.

But there's another possibility See, we humans are now the dominant ecosystem engineers on planet Earth. And while there are very few true megaherbivores left, weve essentially taken over their role in disturbing and opening up forest environments.

So the model suggested that in the long term, the shift in ecological dynamics that we have already set in motion could actually lead to a potential drop in average seed size of 60%!

While fruits origin is rooted in dinosaurs enormous effects on the world around them, the future of fruit on planet Earth will depend mostly on the behavior of a much smaller,