It's a damn good thing dinosaurs planned ahead for those meteorites. Otherwise, we wouldn't have chicken mac nuggets...Huge meat-eating, land-living dinosaurs evolved into birds by constantly shrinking for over 50 million years, scientists have revealed.
Theropods shrunk 12 times from 163kg (25st 9lb) to 0.8kg (1.8lb), before becoming modern birds.
The researchers found theropods were the only dinosaurs to get continuously smaller.
Their skeletons also changed four times faster than other dinosaurs, helping them to survive.
Results from the study are reported in the journal Science.
Previous work has shown that theropod dinosaurs, the dinosaur group which included Tyrannosaurus rex and Velociraptor and gave rise to modern birds, must have decreased in size at some point in their evolution into small, agile flyers.
But size changes frequently occurred in dinosaur evolution, so the research team members, led by Mike Lee, from the University of Adelaide, Australia, wanted to find out if the dramatic size reduction associated with the origin of birds was unique.
They also wanted to measure the rate of evolution in dinosaurs using a large data set.
The authors used sophisticated analytical tools - developed by molecular biologists trying to understand virus evolution - to study more than 1,500 dinosaur body traits coded from 120 well-documented species of theropod and early birds.
From this analysis they produced a detailed family tree mapping out the transformation of theropods to their bird descendants.
It traces evolving adaptations and changing body size over time and across dinosaur branches.
They found that the dinosaur group directly related to birds shrank rapidly from about 200 million years ago.
It showed a decrease in body mass of 162.2kg (25st 7lb) from the largest average body size to Archaeopteryx, the earliest known bird.
These bird ancestors also evolved new adaptations, including feathers, wishbones and wings, four times faster than other dinosaurs.
A broad-billed hummingbird (Cynanthus latirostris) in front of a tooth of a massive dinosaurian.
Shrinking and new bird-like traits jointly influenced the transition of dinosaurs to birds, researchers say.
The researchers concluded that the evolution of the branch of dinosaurs leading to birds was more innovative than other dinosaur lineages.
The authors say this sustained shrinking and accelerated evolution of smaller and smaller body size allowed the ancestors of birds to develop traits which helped them to cope much better than their less evolved dinosaur relatives.
"Birds evolved through a unique phase of sustained miniaturisation in dinosaurs," Mr Lee said.
"Being smaller and lighter in the land of giants, with rapidly evolving anatomical adaptations, provided these bird ancestors with new ecological opportunities, such as the ability to climb trees, glide and fly.
"Ultimately, this evolutionary flexibility helped birds survive the deadly meteorite impact which killed off all their dinosaurian cousins."
oops! Guess they didn't plan for that one. It was good thinking, though, for your average reptile.
I salute the first one who was brave enough to jump out of a tree and try his wings. I guess he figured if he went to the trouble of growing the damn things, they ought to be good for something.
I can see his mama hollering, "Junior, get down. You cannot fly!"
Junior answered, "Oh yeah? That's what they said to Amelia Earhart!"