The connection between birds and dinosaurs is not a new idea. In fact it was a theory championed in the mid 1800s by Thomas Huxley. Most of these ideas were fueled by the discovery of Archeopteryx, the first fossil that really blurred the lines between the bird-like therapods and actual birds. At first they didn't know which side to classify it on. To make it a bird, they had to broaden their definition of birds to include those with clawed fingers and teeth.
We now know that Archeopteryx and its similar cousins make up a subgrouping within Maniraptora (the same subgrouping, Avialae, that contains birds). In the century and half since its discovery, we have come a long way in refining our theory of the dinosaur-bird connection. As we have seen with our look at trying to map out species on the larger Linnaean tree, sometimes it can get really complicated trying to trace a direct lineage of a single species. But with the added evidence of the last number of years, we have gotten closer to finding where your chicken dinner sits on the family tree near its more terrifying cousins.
Though the topic is still up for debate, many paleontologists now group dinosaurs into two major camps (confusingly enough this is different than what we discussed in part 2). They look at dinosaurs as either avian or non-avian species. Non-avian dinosaurs would be the ones that are now extinct like the Utahraptor. While avian dinosaurs would include the extinct Archeopteryx, but also extant bird species we see today. The best part of this idea is that it means dinosaurs are still alive today, and that crow cawing outside my window as I write this, is actually the warning call of a flying dinosaur!
So what makes us think that a roadrunner scurrying across a desert road, is as much a dinosaur as Troodon? Well we have lots of science and evidence to back up the idea. So much in fact that I won't spend my entire day explaining it all, but there are tons of great books on the subject (see part 10).
Have you ever compared the skeleton of a dinosaur and a bird? Okay, I'll admit, probably not everyone. How about seen an illustration of a feathered dinosaur? Hint, look up. Now that we have clear evidence of more and more therapod species sporting feathers and fur-like protofeathers, we start to lose a lot of the distinction between dinos and birds. Just like those 19th century scientists, if we start to include dinosaurs with wings and feathers...
But it goes well beyond just looks. Close examination shows that not only were some of these dinosaurs feathered, but they had specialized feathers with purpose, such as possibly allowing forthe ability to glide.
Therapod forelimbs had bones unlike other dinosaurs. Late therapods had elongated second digits and lost many additional fingers in order to better facilitate wrist movement and eventually allow for the required arm movements of flight. There are even species of living birds that still sport similar claw-like hands.
Their bones were hollow andthin-walled. This allowed them to be much lighter despite their size. Eventually, smaller species, would be able to use that advantage to get them off the ground.
There are dozens of connectionsbetween the two groups, but the most striking evidence has come in the last few years. As well as the discovery of feathered dinosaurs, scientists found an odd connection between birds and dinosaurs where you wouldn't normally think to look. It wasn't just in the fossil record, it was also buried deep within thegenome of modern birds. As geneticists have come to understand more and more about how genes work in the body, scientists discovered that there are many unused genes in bird DNA. Like a row of light switches, scientists went in and began turning them on. These switches were the left over coding from bird's dinosaur past. Some caused a normal breed of domesticated chicken to grow teeth, while others were coding for a longer bony tail. It wasn't long before paleontologist Jack Horner, theorized that you could reverse engineer adinosaur out of a chicken. This was among the strongest evidence yet of the relatedness of birds and dinosaurs.
Check out the final part of this series for recommendations of books and videos for more information on this and the other topics we have only scratched the surface of.
Next time: Part 7 - That's Not a Dinosaur!