Smaller pterosaurs may have flapped their wings while larger ones soared
Terryl Whitlatch
Despite living hundreds of millions of years apart, pterosaurs may be more similar to modern-day birds than previously thought. Structures in the bones of these giant reptiles suggest the largest ones used their wings to soar while the smaller ones flapped through the skies.
The finding comes from stunningly preserved pterosaur fossils unearthed in Jordan. “The mechanics of flight leaves an imprint on the skeleton,” says Jeffrey Wilson Mantilla at the University of Michigan.
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Pterosaurs took to the sky some 80 million years before birds and bats. During their 150-million-year reign from the Triassic to the end of the Cretaceous periods, they conquered all continents and evolved a range of sizes and shapes. Some pterosaurs were as small as a house sparrow, while others had wingspans as long as a city bus. An analysis of their bones suggests different pterosaurs used distinct flight tactics to stay aloft.
Wilson Mantilla and his team compared the remains of two different pterosaur species, and were delighted to find the bones’ 3D structure was still intact. This was a surprise, as pterosaurs’ hollow and fragile bones tend to break down quickly. Computed tomography scans revealed that the two reptiles’ bones were markedly different.
The larger pterosaur, Arambourgiania philadelphiae, had internal ridges that spiralled up and down inside its bones, similar to modern birds like eagles that fly with their wings in a fixed position. Bones of the smaller pterosaur, Inabtanin alarabia – a species new to science – had criss-crossed struts, mimicking those of flapping birds.
The helical spirals help resist the twisting forces of soaring, while crossed scaffolding withstands the bending force of a flap, says Wilson Mantilla.
Because the team found the fossils in a formerly coastal area, he thinks the soaring pterosaurs might have caught sea thermals – updrafts of warm air – to gain altitude. Mantilla suspects these pterosaurs could also flap, especially to get airborne, making soaring the rarer trait.
Why one of these pterosaurs seemed to flap while the other may have soared raises new questions about how the more than 100 other known pterosaur species navigated the skies. Next, Mantilla wants to examine fossils from different parts of the world to see if the pattern holds – perhaps, like modern birds, soaring was reserved for only the largest of their kind.
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