02-03-2025
Like your apples and peaches? An NAU researcher says you might have a dinosaur to thank
A butterfly beating its wings can alter the trajectory of the universe, or so they say. So it's only natural that an event as pivotal as the extinction of the dinosaurs could have some pretty far-reaching effects too.
One of those effects, according to new research out of Northern Arizona University, had to do with fruit. But how, exactly, the demise of the dinosaurs gave rise to the juicy apples and peaches of today is complicated.
Chris Doughty, an associate professor at NAU in the informatics department, investigates how animal extinctions will change our world.
Today, elephants are the largest land mammals. But it's natural for our ecosystem to host huge animals like mammoths, mastodons and giant ground sloths, Doughty said. They evolved in concert with the species, landscapes and systems of our current world — but then they went extinct.
They're thought of as 'relics of the past,' Doughty said, 'but they should be here'.
He uses mechanistic models — essentially computer simulations — to explore how large animals impact ecosystems, and how things like forest structure and nutrient distribution would change if they went extinct.
His research has centered on the extinctions of Pleistocene megafauna, like the aforementioned mammoths and sloths. But in a recent paper, he and other researchers went back even further — 65 million years, to be exact.
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It's long been hypothesized that sauropods — long-necked herbivore dinosaurs such as Brachiosaurus — thinned out forests as they lumbered their way through the trees, eating their fill.
After the sauropods went extinct, the forests grew thicker and darker, which gave trees with larger seed sizes and that bore tasty fruit an advantage. As the theory went, larger seeds gave trees a better chance of reaching light and thriving, while the presence of fruit made it more likely large animals would consume and spread its seeds.
There were patterns in the fossil data to support this, Doughty said, but it felt speculative to him.
'You can obviously speculate that a sauropod is going to knock down a bunch of trees,' he said. 'People have thought about that for a long time. But it's also, just last year we didn't have any hard data on that.'
Coming from an informatics and earth systems background, Doughty had never thought of himself as a paleontologist. Still, he was invited to speak at a paleontology conference about his Pleistocene work.
As part of the conference deal, he had to write an additional paper. Then it hit him.
Why not apply a mechanistic model to the theory about sauropods, forests and fruit?
'I realized I could add something,' Doughty said. There was also plenty of data available to set the parameters of the model.
So he created a model, which he described as a grid depicting a tropical forest, with animals moving around and eating and seeds growing. ('It's not visual,' Doughty clarified, using representations rather than artistic renderings of a 'beautiful mammoth.')
The model was informed by significant data, including chemical analysis of fossilized leaves from Colombia, which allowed researchers to quantify how much less light was in the forest post-dinosaur extinction, and information on how tall a tropical seed will grow based on size.
When researchers ran the model, it closely resembled available data on seed and animal size over time, offering evidence in support of the sauropod forest thinning theory.
As the researchers continued to run the model, it pointed to another trend about 35 million years ago.
Megafauna, though not dinosaur sized, had by then grown large enough to have the same thinning effect on the forest. This diminished the evolutionary advantage for big seeds, and gradually, seeds started to shrink.
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The extinction of the dinosaurs likely paved the way for fruit to take center stage in modern diets.
In our current age, the Cenozoic, 'almost everything eats fruit,' Doughty said. It's now tasty and ubiquitous, but 65 million years ago, it was rare.
'It just was a really niche, small thing,' Doughty said. 'And so it just took this complete reset of the ecology of the planet to really take off. And I think what triggered it was just the darker understory forest canopy.'
Fruit offered an incentive for large animals to swallow seeds and move them far away. That's important because seeds are more likely to die if they grow close to their mother tree, Doughty said.
'Big animals have long legs and big gut lengths so when they swallow a seed they're going to move it much farther.'
While this might seem in the weeds — literally — these changes likely fuelled the evolution of our ancestors.
'It's unlikely things would have happened exactly the same way, that evolution would have come out the exact same way, if this hadn't happened and fruit hadn't developed,' Doughty said.
'Because that's a whole niche that early primates were successful in.'
Some 50,000 years ago, mammoths and other huge mammals were wiped out in another extinction event. The model again predicted an increase in seed size in response to a darker forest.
While most — though not all — believe the dinosaur's fate was sealed by an asteroid, the source of this more recent extinction is much closer to home.
'The data show that everywhere people went, the megafauna went extinct shortly after,' Doughty said.
Like all attempts to understand the distant past, it's not definitive. But it's clear to Doughty that there was a correlation between humans arriving and hunting the animals and the extinctions.
'We're not going out on a huge limb here,' he said.
Today, elephants can affect light levels in the depths of the forest. But the animal that has the greatest effect is us.
'In some ways we're kind of the new sauropods,' Doughty said. 'When we selectively log forests, the light levels are actually quite similar to what we saw was when we had sauropods walking around.'
If humans went extinct — or, in a somewhat less dramatic turn of events, ceased selective logging — the forest understories would likely darken again, potentially triggering another increase in seed size.
'However, if, for whatever reason, humans survive and we're long-term logging these forests, who knows?' Doughty said.
'Obviously it's hugely speculative to say anything about the future of humanity. But it matters for what we're trying to do.'
He acknowledges, with a laugh, that there are other, perhaps more pressing, concerns for the future of humanity right now than seed size.
Then again, look at what happens when a butterfly beats its wings.
This article originally appeared on Arizona Republic: How the extinction of the dinosaurs changed the trajectory of fruit
