Powered flight is a marvel possessed by only three groups of vertebrates. There are birds, of course, and bats. Birds are the usual topic of this blog, as regular readers know very well. And bats, though they are extraordinary creatures indeed, have never interested me to the same degree, perhaps because they are less accessible in many ways. Have you thought of the third group yet? It’s the pterosaurs — ancient flying archosaurs known only from the fossil record. This picture is by John Conway:
I had all the usual dinosaur books and toys as a kid. I don’t know why, but the images of pterosaurs never captured my imagination in any way. Maybe it was because they often looked so emaciated and improbable — stiff, oddly posed creatures colored green or brown. But apparently we’ve learned a lot in the last 15 years, and the latest work on pterosaurs is mind-boggling. My imagination has not only been captured, it’s being held for ransom at a secret facility somewhere in the desert.
Pterosaurs’ wings were supported by astonishingly elongated fourth digits (analogous to your ‘ring finger’). The creatures had hollow bones and and air sac systems, like birds. And they had fur! (For a brief physiological overview, see John Conway’s The Structure of a Pterosaur.)
The pterosaur above is currently identified as Nemicolopterus, thought to be a songbird-sized animal that lived in the forests of what’s now China and subsisted on insects. Chuang Zhao’s stunning depiction contains no trace of caricature and therefore makes this creature seem at once startlingly alive and absolutely alien.
Or, is it? Does that posture look familiar? It should. Vampire bats look remarkably similar when they fold their complex, membranous wings to their sides and run on all four limbs. (Yes, not only can they fly and drink your blood, they can run!) Fossilized pterosaur tracks and skeletal analysis indicate that at least some pterosaurs could move about on all fours, perhaps quite well. Which brings us to…
…Mark Witton‘s breathtaking depiction of Quetzalcoatlus, a giraffe-sized pterosaur with a wingspan estimated at 10 meters or more. In a 2008 paper, Witton and Darren Naish argue against the traditional idea that Quetzalcoatlus plucked fish from the seas like skimmers or frigatebirds, suggesting instead that they fed on land like giant storks. (Greg Laden has a good summary of the paper if you don’t want to read the whole thing.)
And there’s more. Some artists and scientists believe that pterosaurs were brightly colored. Here’s a rendition of Tapejara by Dmitry Bogdanov:
Well, why not? Consider the Helmeted Guineafowl, for instance (Arno & Louise):
Scientists have learned some amazing things about these creatures, but there is much we don’t know and never will. We still don’t know how they actually flew. Analogies with birds and bats can be taken only so far, particularly for creatures that were the size of a giraffe. There’s only so much that could ever be deduced, even if we continue recovering better specimens and are able to refine various models and hypotheses.
Could pterosaurs rapidly change skin colors, like chameleons and some birds? Could they produce bioluminescence? Could they echolocate? Could they sing like birds? Were they polygamous? Did they emit scents? Were they nocturnal (image by John Conway)?
We’ll never know. And frankly, that makes me very sad. Pterosaurs were a very successful, very diverse group of animals that probably filled many of the niches that birds fill today. They lived, and then they died. They ruled the skies, but now all that’s left are a few fragments of their bones.