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article imageSeeds may have helped birds survive extinction of the dinosaurs

By Megan Hamilton     Apr 22, 2016 in Science
While there's plenty of evidence to suggest that dinosaurs were already in decline millions of years before the asteroid impact that spelled their doom, we know that those small, feathered theropod dinosaurs, otherwise known as birds, did survive.
However, this leaves paleontologists with plenty of questions, The Toronto Star reports.
For instance, what caused the dinosaurs to die out when other groups survived? Were the dinosaurs really in decline before the impact? And perhaps the most intriguing question: Why did the ancestors of modern birds make the cut when other feathered dinosaurs became extinct?
Their success may be due to something seemingly inauspicious — seeds.
At the end of the Cretaceous, toothed birds were living alongside birds that didn't have teeth. And when that asteroid hit, they became extinct rather suddenly, while their beak-y counterparts thrived, Cosmos reports.
There were also bird-like dinosaurs, and some had teeth while others didn't. These were meat-eaters, plant-eaters, and others were omnivores — eating plants and meat. But these creatures vanished as well.
A team of paleontologists in Canada, led by Derek Larson, of the University of Toronto, suggest toothed birds may have become extinct because they couldn't eat seeds, as opposed to their toothless counterparts who could.
When the asteroid ploughed into Mexico's Yucatan Peninsula, marking the end of the Cretaceous, it wiped out 70 percent of all life on earth, NASA reports. Yet somehow, "modern [toothless] birds managed to survive the extinction," Larson said.
"The question is: why did that difference occur when these groups were so similar?"
Larson and his team set to work, studying 188 current bird species and tracing them to a common ancestor.
They discovered that this ancestor was a bird-like dinosaur with a toothless beak, and seeds were part of this creature's diet. Even though the asteroid impact kicked up a layer of dust that blocked the sun, these toothless creatures could maintain their seedy diet. And that diet was probably supplemented by seeds from flowering plants (angiosperms), which would have been one among very few food sources still available, even in the acid rain and enormous fires that raged in the aftermath of the impact.
Their study, published in the journal Current Biology, may explain why modern birds don't have beaks lined with teeth, BBC News reports.
"After this meteor, you're left with essentially a nuclear winter where really not much is growing, the plants aren't able to grow to provide nourishment for plant-eaters and then meat-eaters aren't able to access plant-eaters if they've all perished," Larson said. "We think that the survival of birds had something to do with the presence of their beak."
The scientists studied fossilized teeth from more than 3,000 maniraptorans (bird-like dinosaurs). These dinosaurs are close relatives of modern birds, but when the Cretaceous period ended, most vanished, including the toothed birds.
Studying the diet of modern birds, Larson and his colleagues were able to reconstruct a hypothetical ancestral bird and what it likely ate.
The beak of this seed-eating bird would be relatively short and robust; strong enough to crush seeds, Larson said.
Most of the birds we see today would not be around if it were not for their seed-eating ancestors, although some birds, perhaps those that eat insects, may have survived the impact.
"We might be looking at a very different picture of bird diversity had certain groups not evolved the ability to eat seed material," he said.
While seeds may well have helped birds survive, they were not likely the solution for every creature that survived the impact, The Christian Science Monitor reports.
"We're not saying that this is the only way that anything survived the mass extinction," Larson says. "For instance, crocodilians survived the mass extinction and we're not proposing that crocodiles and alligators were chomping on seeds. Their teeth are entirely unsuited to that."
Larson's theory is nearly in lockstep with research regarding another paleontological quandary: Were the dinosaurs struggling or thriving before the asteroid spelled their doom?
The team of researchers in this instance used statistical analysis to study trends in dinosaur diversity across all species, whereas Larson's team focused on bird-like dinosaurs, specifically their teeth.
As another facet of their study, the researchers examined the shape of the teeth in order to find out if this group was changing in response to ecological stresses prior to the asteroid strike.
But in this particular group, Larson found no decline as the end of the Cretaceous loomed.
"In fact, this group of dinosaurs went extinct very suddenly" he said.
The researchers studying whether dinosaurs were in decline even found that if Earth had never been hit by the asteroid, they still would likely become extinct, The Los Angeles Times reports. In fact, their research shows that decline began millions of years before the impact.
The results of that study were published Monday in the Proceedings of the National Academy of Sciences, and it showed that as early as 40 million years before the Chicxulub asteroid landed, dinosaur species were becoming extinct faster than new ones were evolving. The authors concluded that with a dearth of species, and less variation in habitat requirements and ecological niches, dinosaurs would be less likely to capably handle environmental changes, the authors wrote.
Which means that one dinosaur — the birds — reaped the seeds that evolution sowed.
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