Feathered Dinosaurs

An artist's rendering of Yutyrannus huali, a feathered dinosaur recently discovered in China.

I wanted to alert everyone to an article that appears in the journal Nature today, which has been causing quite a stir.  (It was even written up in the NY Times!)  The article announces the discovery of a new feathered dinosaur from the Lower Cretaceous in Liaoning Province, China.  Above is an artist's rendering that gives you a sense of how scientists imagine these creatures looked in the flesh.

There are a few things worth noting here.  First, this creature is a fairly close (but older) relative of T. rex.  Second, as the article points out, it is by far the largest feathered dinosaur that has been found so far.  (The next largest was only about 1/40th its size.) 

Since the discovery of Archaeopteryx in the Victorian period, paleontologists have posited a link between extinct dinosaurs and modern birds.  (Indeed, extinct dinosaurs are now usually referred to as non-avian dinosaurs.)  But in the past several decades, scientists have been pushing the evolution of feathers further and further back, both temporally and phylogenetically.  Archeopteryx was a kind of transitional form, whereas Yutyrannus huali is nested relatively deep within the Tyrannosaurid family tree.

But there's another, perhaps even more interesting reason why the relationship between this creature and the famed Tyrannosaurus rex is so important.  Previous discoveries of feathered dinosaurs have resembled a chicken more so than the creatures we usually associate with the name "dinosaur."  This most recent finding changes that completely.  Now we have something that looks very much like a canonical (non-avian) dinosaur, yet it appears to have been covered with a downy plumage!  Part of the reason this animal has made such a stir, I think, is therefore the fact that it gives license to artist's renderings of the type pictured above.

Anchiornis huxleyi, a feathered dinosaur from Liaoning Province, China.

By way of contrast, consider the example of A. huxleyi (pictured above), which was also discovered in Liaoning Province, China.  In an article published in Science, researchers from China and the United States were able to infer the specimen's color pattern from microfossilization of melanosomes.  You've probably encountered the picture before, because it also made a big splash in the popular press.  Here, the animal cannot boast of a particularly impressive size, but scientists were able to endow it with a visually striking color pattern.

All of this obviously looks very different from how we used to think about dinosaurs.  The most famous and prolific visual interpreter of prehistoric animals during the heyday of dinosaur research around the turn of the 20th century was undoubtedly Charles R. Knight.  Unlike these modern, active, colorful creatures covered in feathers, Knight painted dim-witted, slow-moving, scaly, and drab reptiles.  

T. rex battling a Triceratops, by Charles R. Knight. 

   

So, what's the relationship between material evidence and imagination in producing these illustrations?  Why have our visual renderings of dinosaurs changed so much over time?  I think the answer is neither just cultural -- artists are simply making it up as they go along -- nor is it just empirical -- artists are simply following the available evidence.  Rather, the two interact with one another in a very deep way.

In the comments section of the previous post, Hank, ST(res)S-ed out, and I have been arguing about Ian Hacking's ideas about "dynamic nominalism" -- the extent to which our interpretation of the world changes its material constitution.  I don't want to suggest that dinosaurs are historically constituted in precisely the same way that Hacking thinks people are -- that is, I don't think that what we think about dinosaurs actually changes the material fossils buried underground -- but I do think that *something* comparable to Hacking's dynamic nominalism is going on here.

You might ask yourself (as I often do): why were feathered dinosaurs (of the non-avian variety) not discovered until so recently?  Prior to the discovery announced in Nature today, you might have said: perhaps because feathered dinosaurs are relatively modest in terms of their size and appearance.  (Modest until you have the tools to reconstruct their plumage pattern, that is!)  But as I've already noted, part of what makes this discovery significant is that Y. huali is a close relative of T. rex.  The next obvious question, to my mind, is this: if big, impressive, therapod dinosaurs like Y. huali had feathers, why didn't anyone notice until now?  Is it because paleontologists have only begin to research the evolution of dinosaurs in China, which is where feathered dinosaurs tend to be found, relatively recently?  Or is it because paleontologists simply weren't looking for feathered dinosaurs during the early 20th century, when the Western United States was understood to harbor the world's richest dinosaur quarries?  

Figure 2 from the Nature article, images c-h showing "preserved integumentary structures," i.e., fossil feathers, in Y. huali.

If you read the Nature article carefully,  and especially if you examine the Y. huali fossil (pictured above) closely, you'll see that it's not at all obvious, at least not at first glance, that this creature had feathers.  So I could easily imagine someone preparing this specimen, trying to free the bones from the rock matrix, inadvertently destroying the fossilized traces of feathers.  Perhaps the only reason Y. huali was recognized to have had feathers is because by now paleontologists are actively on the lookout for them.  If that's right, then what's in your mind when you prepare a fossil for study and display may well have a significant impact on the material constitution of dinosaur bones.

All of this is to say that I am now anxiously awaiting the day when paleontologists working in the American west announce the discovery of a downy T. rex!