July 10 , 2016

by Brian Switek

Dinosaurs still roam the Earth. You don’t even have to go to a distant swamp or an isolated jungle plateau to see them. They’re everywhere – waddling over Antarctic ice, sprinting through the Kalahari, soaring over the Andes, dropping guano on the traffic of New York, and being served up crispy by fast food chains.

Birds – from emu to hummingbird – are the sole surviving dinosaur lineage. You probably knew that, you smart cookie. But you might think that any real family resemblance has been lost to evolutionary changes. In fact, if you know what to look for you can spot plenty of dinosaur traits in your average ol' bird.

Compared to the amazing variety of vertebrate life on this planet, birds stand out. They are the only animals with feathers, for starters, not to mention other specializations like a complex air sac system that keeps their bones light while making them especially efficient at drawing oxygen from the air. But it’s only when we look into the depths of prehistory that the truth becomes clear: Many of the characteristics that we think of as unique to birds were also common among their unlucky, extinct cousins – the non-avian dinosaurs that haunt museum halls.

Imagine the kinds of wishes you could make on that bad boy.

Specialized air sacs were also thought to have been uniquely avian at one time. These internal balloons – which not only help make bird skeletons light, but also make bird breathing superior to our simple in-and-out method – run out of the bird respiratory system to indent or even invade bones.

The most telling hallmark of birds’ dinosaurian ancestry, however, is their feathers. Since 1996 paleontologists have uncovered a wealth of fossils from all over the world that have left no doubt that many non-avian dinosaurs were clad in protofeathers or similar, feather-like structures. The simplest of these are tubes that would have given dinosaurs like Compsognathus the look of a newly-hatched chick. Others are more complex, branching and carrying locking barbs, laying out the evolution of the feather from a singular wisp into an asymmetric structure capable of providing lift.

Regardless of which turns out to be true, it’s clear that feathers did not first evolve for flight. Protofeathers evolved for insulation and display at the outset were eventually co-opted to other uses -- like flapping to give clawed feet a better grip on inclined surfaces and, eventually, flight. Soaring through the air was an unexpected happenstance that rose out of feathers spreading far and wide through the dinosaur family tree. Think about that the next time you see a turkey vulture lilting overhead or a pigeon frantically fluttering off the curb. Those birds are the kin of Velociraptor, and the Age of Dinosaurs continues to this day.