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Bird-like dinosaurs with toothless beaks survived the "nuclear winter" that followed the meteor strike, because of their diet, a study says. The impact altered the climate of the Earth and blotted out sunlight. The loss of vegetation would have deprived plant-eating dinosaurs of food. In turn, meat-eaters suffered. But seeds still in the ground may have sustained small toothless bird ancestors until the planet began to recover.
The theory, outlined in the journal Current Biology, could explain why no modern bird has a beak lined with teeth. "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," said lead researcher Derek Larson, from the University of Toronto. "We think that the survival of birds had something to do with the presence of their beak."
Some groups of beaked birds may have been able to survive the extinction
Fossil teeth
The researchers studied more than 3,000 fossilised teeth from bird-like dinosaurs known as maniraptorans. These dinosaurs are some of the closest relatives of modern birds - but, at the end of the Cretaceous period, many disappeared, including the toothed birds. The team suspected diet might have played a part in the survival of the ancestors of modern birds. "We came up with a hypothesis that it had something to do with diet," Mr Larson said. "Looking at the diet of modern birds, we were able to reconstruct a hypothetical ancestral bird and what its likely diet would have been," he told the BBC's Science in Action programme. "What we're envisaging is a seed-eating bird, so you'd have a relatively short and robust strong beak, which would be able to crush these seeds."
Mr Larson said most of today's birds would not be around if it were not for their seed-eating ancestors, although a handful of other birds might have survived the impact, perhaps through eating insects. "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. The dust in the atmosphere from the strike of the huge comet or asteroid would have obscured sunlight and blocked photosynthesis. However, seeds that had already built up in the ground would have still been available as a food source for anything with a beak capable of eating them.
Seed clue to how birds survived mass extinction - BBC News
At birth, titanosaur babies weighed about as much as average human babies, 6 to 8 pounds. But in just a few weeks, they were at least the size of golden retrievers, weighing 70 pounds. And by age 20 or so, they were bigger than school buses. That jump from something that you could hold in your hands to one of the largest creatures to ever roam Earth beats anything scientists have seen before in terms of growth, said paleontologist Kristi Curry Rogers of Macalester College in St. Paul, Minnesota. She is lead author of a new study on the baby dino fossils published Thursday in the journal Science.
A fourth grader inspects the replica of a 122-foot-long dinosaur belonging to a group known as titanosaurs on display at the American Museum of Natural History in New York
By comparison, modern giants like whales, elephants and hippos are born much bigger than titanosaurs. Jeff Wilson of the University of Michigan, who wasn't part of the study, said it is the paradox of this class of dinosaurs: They started out as tiny eggs and ended up as the largest animals on the planet. Titanosaurs, plant-eating dinosaurs which lived about 67 million years ago, grew to be 15 feet tall, not including their necks and heads. They could stretch out to be 50 feet long. Looking through old bones stored in a museum after a dig in Madagascar, Rogers found enough small bone fossils to reconstruct a soon-after-hatching rapetosaurus, a type of titanosaur. The baby dinosaur died of starvation during a drought that killed many others in the region, she said.
Puppy-like cuteness
And, yes, you could call it cute. “There is no doubt that these baby titanosaurs would have had some of the features we would normally associate with cuteness or baby-ness: short snout, large eyes, big head for a body — like a puppy,'' said Luis Chiappe, director of the Dinosaur Institute at the Natural History Museum of Los Angeles, who wasn't part of the research but praised it.
The American Museum of Natural History unveils an exhibit of a 122-foot-long dinosaur which belongs to a group known as titanosaurs
The fossils confirmed that these creatures were precocious, Rogers said— they hatched from the egg pretty much ready to walk and live on their own. It would have been hard for the giant parents to care for their babies. They had 20 to 30 softball-size eggs in a nest and when they hatched, it would have been hard for the adults “to keep track of all the babies around their feet,'' Rogers said. “It was just a free-for-all.''
From Tiny to Titan: Baby Dinosaur Fossils Reveal Megagrowth
