Pterosaurs: The First Flyers

The pterosaurs are divided into two groups. The primitive Rhamphorynchoids appear during the late Triassic Period, and died out around the end of the Jurassic Period. They had long tails, short necks, and short skulls, and were very small, some were as small as sparrows. The Rhamphorynchoids included Dimorphodon, Rhamphorynchus, and Sordes.

The Pterodactyloids appear in the late Jurassic Period, and died out at the end of the Cretaceous Period. They had shortened tails, and longer necks and skulls. They also had longer metacarpals, the long finger that supports the membraneous wings. The Pterodactyloids were also larger than the rhamphorynchoids, and included Quetzalcoatlus, Dsungaripterus, Pteranodon, and Pterodactylus.

Pterosaurs are often portrayed as being poor flyers that relied mostly on gliding, but the small Rhamphorynchoids were probably capable of active flight to a degree similar to that of modern birds, probably more so than Archaeopteryx. The larger Pterodactyloids probably relied more on gliding than continuous flapping for flight, the same way that large extant birds do. They were probably restricted to areas with regular, gentle winds throughout the year.

Although Pteranodon has been shown by computer models to have been a rather slow glider, it probably had a very tight turning radius, allowing it to manoeuver quickly in the air. Pteranodon probably did not catch fish with its feet, the way extant birds of prey do. This would have caused Pteranodon's center of gravity to be shifted so far back that its flight would have been stalled. Instead, it is believed that Pteranodon caught fish with its beak, and may have carried them in a throat sac, similar to that of the modern pelican. (Some recently analyzed specimens of Pterodactylus from Solnhofen show this feature!) This would have only displaced its center of gravity a small amount, and would not have caused flight to stall.

Like the bones of birds, the bones of pterosaurs have air sacs that were extensions of their lungs, and helped to decrease their weight. Even though Pteranodon had a massive wing-span of more than eight meters (26 feet), it weighed in at only sixteen kilograms (35 pounds).

A dramatic decline in pterosaur diversity, and the end of the Rhamphorhynchoid lineage at the end of the Jurassic coincided with the emergence of birds, and some paleontologists believe that this may have been due to competition between the two groups. Birds have some advantages

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