Saturday, May 16, 2009

Grounded

Scientists are complaining that the new Dinosaur movie shows dinosaurs with lemurs, who didn't evolve for another million years. They're afraid the movie will give kids a mistaken impression. What about the fact that the dinosaurs are singing and dancing? ~ Jay Leno

For a bunch of critters that went extinct around 65 million years ago, before even I was born, dinosaurs are always popping up in scientific news. On the one hand, new species are regularly turned up, which is not surprising, really. We find new species of living animals all the time. When we see the variety of life on the planet now, then the creatures we've dug up can only amount to a tiny percentage of all the beasties that walked the planet millions of years ago.

On the other hand, scientists keep developing theories about the dinosaurs we do know about. Dinosaurs used to be lumbering tail-dragging lizards, clomping across the landscape. It's now generally agreed that there were a lot of very agile dinosaurs, including some of the big ones. And few if any of them dragged their tails; the tails actually streamed straight out behind the dino, providing balance and, in some cases, a defensive weapon. And some were warm-blooded, not lizard-like at all.

So the vision of lumbering giants spending their time half-submerged in some swamp has been replaced by mobile herds of sauropods grazing their way through entire forests, while being bushwhacked by the occasional allosaur or T-rex, depending on the geological era. Of course, there seems to be considerable disagreement these days over tyrannosaurus rex himself. He was fast, he wasn't fast, he was an accomplished pack hunter, or he was just a scavenger. Oh, and he may have been covered by feathers, at least as a juvenile.

But, no matter how you envision the dinosaur age, one part of the picture never changed: The sky was always filled with flying pterosaurs. Not so fast, says Katusfumi Sato.

If you're like me, you've always had a bit of a disconnect between imagining the soaring pterosaur and imagining one on the ground. In particular, if you really thought about it, you had the nagging feeling that it had to pretty hard for a pterosaur to get off the ground. Trying to imagine quetzocoatlus, a pterosaur with a wingspan the length of a school bus, getting airborne was difficult. According to Prof. Sato, it was probably impossible for the largest specimens.

One could speculate that these were cliff-dwelling animals that could launch themselves from the lofty reaches and soar around with impunity. The trouble is that any large pterosaur that landed on the ground would have a serious problem ever getting airborne again. That would not bode well for their continued existence. Sato even debates whether their fragile wings could have supported them in the air at all.

Of course not all paleontologists agree with this view. They point out that using studies of modern birds may not be a good model for the more reptilian pterosaur. Perhaps the atmosphere was more dense (a distinct possibility), or gravity was lower (not very likely). At any rate, it is quite possible that the rules for pterosaur flight were different those governing an albatross, just as the flight rules for a bumblebee are different from that of an eagle.

One rather weird suggestion is that perhaps the pterosaurs were flightless and used their wings for swimming, like penguins. Unfortunately, as one scientist points out, the wings "do not look very efficient for swimming." In fact, it's hard to imagine the thin membrane being able to hold up against the rigors of underwater propulsion.

Some years ago, someone actually built a lifesize model of quetzalcoatlus, which was about the size of a decent ultralight aircraft. They equipped it with motors to make the wings flap and actually got the contraption airborne. Once in the air, the model performed quite well, soaring along nicely, fitting our classic view of the magnificent pterosaur ready to swoop down on its prey. Lovely image, but they did not try to get the thing flying from a standing start. They actually towed it like a glider then released it into flight. Since we can rule out quetzalcoatlus having friends with towing vehilcles, that still leaves open the issue of how he got into the air in the first place.

Prof. Sato has his critics and is by no means the last word on the subject, but we just may have to give up that image of the majestic flying reptile.

At least we still have the feathered theropods.

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