Pterosaurs Evolutionary Late Bloomers

Pterosaurs ruled the sky with a body form that worked for 70 million years.

Pterosaurs soared over the dinosaurs for millions of years without evolving to fill specific niches in the ecosystem. They stayed generalists. It wasn't until birds showed up that the flying reptiles started getting creative with their evolution.

Pterosaurs were the first vertebrates to take to the skies. The pterosaurs took off in the Triassic Era about 220 million years ago, and for 70 million years they stuck with the same basic body plan. Research published in the Journal of Systematic Paleontology looked at the late-blooming pterosaurs' evolutionary history.

"Usually, when a new group of animals or plants evolves, they quickly try out all the options. When we did this study, we thought pterosaurs would be the same," said Katy Prentice, an undergraduate researcher at the University of Bristol, in a university press release.

"Pterosaurs were the first flying animals – they appeared on Earth 50 million years before Archaeopteryx, the first bird – and they were good at what they did. But the amazing thing is that they didn't really begin to evolve until after the birds had appeared," said Prentice.

"Pterosaurs were at the height of their success about 125 million years ago, just as the birds became really diverse too," said Marcello Ruta, Prentice's supervisor. "Our new numerical studies of all their physical features show they became three times as diverse in adaptations in the Early Cretaceous than they had been in the Jurassic, before Archaeopteryx and the birds appeared."

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Prentice and her supervisors studied 50 different pterosaurs, ranging in size from as small as a blackbird to the giant Quetzalcoatlus.

Early pterosaurs, called rhamphorhynchoids, were all about the same size and shape. They ate either fish or insects and didn't have wingspans much greater than 2 meters (6.6 feet).

Then in the late Jurassic and early Cretaceous, pterosaur diversity exploded. These later pterosaurs are called pterodactyloids.

Some of these new pterosaurs grew as tall as giraffes, like the enormous Quetzalcoatlus with a wingspan of more than 10 meters (32 feet). They also developed fancy headgear and specialized teeth.

Discovery News reported on engineers' attempts to use pterosaur crest designs to improve aircraft maneuverability.

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The different types of crests may have had some effect on flight, but many researchers believe crests may have been more important for helping pterosaurs find mates. Modern birds, descendants of the pterosaurs' dinosaur cousins, use crests and other displays in much the same way.

The teeth may have been a reaction to new food sources that became available in the Cretaceous as well. The Cretaceous Terrestrial Revolution marked a dramatic change in plant and animal life on the ground. The pterosaurs may have been diversifying to take advantage of the new grub.

The appearance of birds may have also given pterosaurs a run for their money.

But trying to determine whether it was the new diversity of food sources or the appearance of birds that caused pterosaurs to diversify is like asking, "Which came first, the Archaeopteryx or the egg?"

IMAGE 1: Diversity in cranial characters of the pterodactyloid pterosaurs, showing variations in jaw shape, presence and absence of teeth, skull proportions, and crests on the snout and back of the skull. Pterosaurs shown are: A, Dimorphodon; B, Rhamphorhynchus; C, Coloborhynchus; D, Pteranodon; E, Pterodactylus; F, Pterodaustro; G, Dsungaripterus; H, Tupandactylus; I, Thalassodromeus. (CREDIT: From University of Bristol press release; Drawing by Mark Witton.

IMAGE 2: Extremes in pterosaur morphology. The giant and probably flightless Quetzalcoatlus from the Late Cretaceous of Texas was as tall as a giraffe. The small insectivorous Anurognathus from the Late Jurassic of Germany is seen flying above the artist's head. (CREDIT: From University of Bristol press release; Drawings by Mark Witton.