It's a bird, it's a bat, its...?

Here's a critter you don't see everyday:

Dsungaripterus weii, Cincinnati Zoo, OH, 3/29/2012

Dsungaripterus weii, Cincinnati Zoo, OH, 3/29/2012

This, as far as I can tell*, is Dsungaripterus weii, a Dsungaripterid pterosaur from the early Cretaceous. This particular one hangs out in the bird house at the Cincinnati Zoo, but in life, it flew around what is now western China.

As a birder, I have to admit, I find pterosaurs fascinating -- not only were they the first chordates to develop flight, but they showed a truly amazing range of ecological adaptations, from small creatures that may have behaved like Whip-poor-wills (Anurognathids, described by Mark Whitton as Muppet-faced) to truly gigantic Azdarchids, including Quetzelcoatlus, with 10.5 meter (That's 35 feet!) wingspans, thought to be the largest creatures ever to laugh at Earth's attempts at gravity. (1) 

They also help provide a useful lesson in evolution -- I mentioned that they were the first chordates to develop flight. Well, here's an example of the second group:

Herring Gull (Larus argentatus)
Lake County Fairgrounds, 2/14/2014

And here's one from the third group:

Straw-colored Fruit Bat (Eidolon helvum), Omaha Zoo, NE, 12/30/2012

Obviously, the second one is a bird (a Herring Gull (Larus argentatus) to be precise), and the third one is a bat (a Straw-colored Fruit Bat (Eidolon helvum)). Now, clearly, for a creature to fly, it needs some sort of a wing. Ancestral tetrapods had four limbs (hence the name tetrapod!), and while species have lost some, no species of tetrapod has developed a fifth (or sixth, etc.) limb. So if we're going to grow wings, they're going to have to be variations on one of the four. All three groups developed wings using the forelimbs, although bats and pterosaurs both connected their wings to their legs to help with control. Three out of three isn't exactly a statistically significant sample, but the physics strongly suggest that hind limb wings would be very difficult to use, so it probably isn't a coincidence.

But look at those wings! The bat does things, I would think, the most sensibly. The fingers elongated, and the skin between them no longer dies back during development, leaving them with extensive webbing. You can see the long fingers in this shot. The pterosaur did something a bit funny - only one finger elongated! The webbing extends back from that finger to the leg bones, but all of the bony structure of the wing is at the front. (Soft-part fossils suggest that there were tendons running through the membrane, so it was well supported.). Birds, on the other hand, basically got rid of their fingers! Looking at that bird's wing, the only place where the feathers are concealing bone is the dark part (the way the color delineates it is a quirk of this species and plumage, not a general characteristic). The joint halfway out that looks like the elbow is actually the wrist, and the hand bones beyond it are almost entirely fused - think about the end of the chicken wings you may have had for lunch.

So we have three lineages, each of them very successful. (Pterosaurs are extinct, yes, but they lasted 150 million years or so first.) They show some definite convergences (in addition to wings at the front, they all show compact bodies, high shoulder joints, and several other adaptations to flight) where physics leaves no choice, but each one approached the problem with a different historical background, a different anatomy, and a different set of ecological needs (well, I assume that that last one is true, anyways). Wonder of wonders, they achieved a common goal in three very different ways!

Evolution works like this. Where physics, chemistry, and ecology provide simple constraints, we should expect convergence. But wherever there's room for experimentation, critters are going to show the results.

*Corrections welcome, of course! 

(1) Mark P. Witton. (2013) Pterosaurs: Natural History, Evolution, Anatomy. Princeton, NJ: Princeton University Press.