While Jurassic Park-style, meat-eating dinosaurs thankfully are not around anymore, their descendants are still roaming among us. Turns out, they simply shrank in size, evolving into our feathery companions.
We have known for years that all modern birds evolved from dinosaurs, but a new study published in the journal Science this week shows that the key to this amazing transformation was for one particular group of giant lizards to continually get smaller and smaller over a 50-million year span of time. It was a unique evolutionary event amongst the entire kingdom of dinosaurs.
“No other dinosaur group underwent such a long and extended period of miniaturization. Statistically this trend was far longer than would be expected - analogous to flipping a coin a dozen times and getting all heads,” said lead author of the study Michael Lee, an evolutionary biologist at the University of Adelaide and the South Australian Museum in an interview with Yahoo Canada News.
“Also our study measured the rate of evolution of different groups of theropod dinosaurs, and the fastest-evolving group also happened to be ancestral to birds."
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Lee and his team looked at over 1,500 anatomical traits in 120 meat-eating dinosaurs, and using complex mathematical models were able to create family-trees, looking at relationships and evolutionary rates.
“The mathematical tricks to do this were developed over a decade ago by molecular biologists trying to reconstruct virus evolution, so we transferred those methods across and used them to compute our dinosaur tree, and look at their evolutionary dynamics,” he explained.
Paleontologists looking at fossils of meat-eating dinosaurs, particularly those that were small bipedal like the Veloceraptors, have pointed out years ago how they share an uncanny number of traits with modern birds: everything from wishbones, light hollow skeletons, three-fingered hands that folded like bird wings and an array of bright, complex feathers. Many of them also had some ability to glide, perhaps even fly.
In fact, Lee says that the line has been blurred so much that it now has become impossible to draw the line between an advanced bird-like dinosaur and a primitive dinosaur-like bird.
But one thing is for sure, evolution favoured smaller, more limber-bodied dinosaurs able to fit into new types of habitats that were out of reach to their big brothers.
“It would have permitted them to chase insects, climb trees, leap and glide and eventually develop powered flight,” Lee explained.
Since small bodies lose heat more rapidly, feathers offered ideal heat insulation.
“Large bodied endotherms generate so much body heat they have problems losing it, for example elephants have evolved hairless and big ears to dissipate heat.”
When the doomsday 10 kilometre-wide asteroid hit some 66 million years ago, the fastest-evolving dinosaurs — those that had become birds — actually had what it took to survive the global catastrophe.
“[The ability of ] flight allowed them to range over wide distances in search of suitable habitat, and endothermy and good insulation would have buffered them against the ‘meteorite-winter,’” Lee said.
Now Lee and his team are interested in doing similar investigations with mammals to see how their ancestral evolutionary tree may have sprouted.
“Mammals are known to have underwent a burst of evolution after the non-avian dinosaurs all went extinct,” he explained.
“[Questions remain as to] just how fast did they evolve, and for how long did this evolutionary spurt last?”
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