National Geographic recently had a beautiful spread on pterosaurs- those ungainly creatures that nobody thought could fly, until, apparently, we realized they really did fly. Indeed, they ruled the skies for over 160 million years- far longer than birds have. They operated a good deal like bats, with wings of membrane spread between modified fingers, which also stretched back to their legs. But a crucial difference is that, unlike bats, pterosaurs used only a modified fifth finger to carry the outside of the wing. The other fingers made up a strong hand about mid-wing that could be used for walking and lifting off. Thus pterosaurs were much better walkers than bats, and could also lift off from a standstill more effectively.
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| Reconstruction of the largest known pterosaur, Quetzalcoatlus, as tall as a giraffe, from the late Cretaceous. |
What remains astonishing is how much apparent weight these animals carried, especially in front. The largest known pterosaur, Quetzalcoatlus, weighed about 440 pounds and had an enormous head. The head may have been quite thin, but, with neck, takes up roughly half its length. All pterosaurs tended to have large heads, and frequently added remarkable crests or horns, as if snubbing their beaks at aerodynamics. But looks are deceiving, since, like the toucan's bill, pterosaur crests and bones are hollow, very thin (1 mm), and thus were very light. The classic Pteranodon, with a crest almost as long as its enormous bill, is estimated to have weighed only 25 pounds, easily carried by a wingspan of 25 feet. Whether they could have carried off the hapless Zara Young is another matter.
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| Beautiful specimen of Rhamphorhynchus, from the Jurassic, with impressions of wing and tail membranes. |
What is almost as compelling as the fossils of pterosaur bones are fossilized trackways, which show them in action. Over thirty walking tracks have been found, and one paper even describes what the authors interpret as a landing track. Typical pterosaur walking tracks show the heavier hind feet on the inside, and the wing/hands much more lightly on the outside. At each stride, the rear feet pull up roughly parallel to where the wing/hands have just left (b, in the figure). In these novel tracks, which begin abruptly, there are only hind feet for two strides, before the wing/hands appear. Secondly, the first hind feet tracks have elongated claw marks. Thirdly, the first two or three hind foot track sets are parallel and show a very short stride, different from typical walking gaits, of which the rest of this track is an example. These characteristics all lead to the idea that this pterosaur was landing, and hopped a couple of times with both feet before transitioning to a walking gait.
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| 150 million year-old tracks from France. Top is an interpretation of the middle tracks, as evidence of landing. Below is a typical walking sequence and interpretation from the same location / source. The scale bar at bottom is 10 cm, so this pterosaur was relatively small. |
This is not new work, dating from 2009, but the message is still a little hard to wrap one's head around- that tens of millions of years went by with these incredible creatures carrying on the battle for survival, with great success, and high style as well.
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| Nyctosaurus gracilis, reconstructed, from the late Cretaceous. |
