Thursday, January 08, 2009

Jurassic birding

I was surfing through Wikipedia last night for some info on bird taxonomy, which lead me into pages about bird evolution and dinosaurs. Of course, we all know in a general sense much of the work of recent decades demonstrating the close relationships between birds and dinosaurs. What I had not really appreciated, though, was that it is now nearly universally accepted in paleontological circles that birds are not just descended from therapod dinosaurs, they still are therapod dinosaurs. I knew there were many who had made this suggestion, but I didn't realize that it had actually become the accepted mainstream view. The "classic" dinosaurs are now refered to as the non-avian dinosaurs.

Apparently recent fossil finds, especially in China, have pretty well erased the distinctions between birds and dinosaurs. Most of the traits that were considered Class-level defining characteristics of Aves have been found to be widespread in dinosaurs and inherited by birds from them: such things as feathers, hollow bones, and homeothermy were distinctive dinosaur traits as well. Sorry to break the news to Hollywood and Michael Crichton, but Velociraptors were apparently feathered. About the only things left that separate all modern birds from dinosaurs are the short fused tail and modifications to the shoulder to allow powered flight. Well, these are hardly class-level traits, and Archaeopterix, universally viewed as a bird, had neither! We great apes have modified shoulders and short fused tails relative to most of our mammalian cousins, but that hardly makes us non-mammals. I've always thought that birds, in spite of their great diversity, actually have far less variation in their fundamental body architecture than do the other amniote classes. Think of mammals, ranging from bats to whales, and reptiles, which include turtles and snakes. In that context the difference between a penguin and a hummingbird doesn't seem so great. But if in fact modern birds are just one sub-branch off of the larger class of dinosaurs, then the variety gets more comparable (now it's Tyrannosaurus to Archiolochus).

This leads me to wonder two things (one serious, one jesting)... First, when will these changes be reflected in the Linnaean taxonomy? Don't the Class lines among reptiles, dinosaurs, and birds need to be redrawn? Have the AOU and BOU even begun to think about this? Actually, given that Aves has been known longer than dinosaurs, doesn't this mean that dinosaurs should be moved into Aves instead of vice versa? In terms of nomenclature it would seem by the rules of precedence that bird are not dinosaurs; rather, dinosaurs are in fact birds.

Second.. if some real-life Jurassic Park type person actually does clone some cute little ("non-avian") dinosaur, and it manages to survive our drastically lower atmospheric oxygen than what prevailed when it last lived, and it escaped and got established in the wild, would it be countable as a bird?


At 4:02 PM, Blogger John B. said...

That's one classification puzzle I'm glad I don't have to figure out. I guess one question that would arise from putting dinosaurs into Aves would be what to do with the non-avian dinosaurs. Whither Stegosaurians?

At 8:36 AM, Blogger Martin said...

if you can get it, this book is worth a look.

Feathered Dinosaurs: The Origin of Birds
John Long & Peter Schouten.
Oxford University Press
ISBN 978-0-19-537266-3

At 11:24 AM, Blogger Floyd Hayes said...

Archaeopterix? Speaking of ghost birds, there's more evidence that Campephilus principalis still exists than Archaeopterix ever existed. Why it's never even been described!

Did you mean Archaeopteryx with a "y"?


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