November 12. Pterosaurs

To start with today, I have a correction. In the episode for October 29, when I was talking about cycads, I misrepresented some research I cited. I said the study indicated that cycads had gone extinct and then re-emerged 10 million years ago, but the study was actually talking about a radiation, a rediversification, of cycads 10 million years ago, following a decline from the end of the Cretaceous. I’m sorry for this mistake, which has been corrected in the online blog post. Thanks to an anonymous commenter for pointing out my error.

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Back to the Cretaceous.

Drawing of Quetzalcoatlus feeding by
Mark Witton and Darren Naish,
used under Creative Commons license.

We have to talk about pterosaurs again, because during the Cretaceous they became the largest flying animals in the history of the earth. Pterosaurs were reptiles, but not closely related to dinosaurs nor to the birds that were descended from dinosaurs. They were the first vertebrates to achieve true flight.

They were really quite diverse, and not all of them were huge. The smallest known pterosaur is a specimen from the Jehol Biota of northeastern China, a not-quite-adult pterosaur with a wingspan of about 25 centimeters, or 10 inches. It lived in early Cretaceous time, about 120 million years ago.

At the other end of the size spectrum, two specimens have been found that date to the last 4 million years or so of the Cretaceous Period, about 70 to 66 million years ago. Quetzalcoatlus was discovered in the Javelina Formation at Big Bend National Park, Texas in 1971. You’ll see estimates for its wingspan up to 16 meters or 52 feet, but the consensus today seems to be more like 11 meters or 36 feet – still huge, given that the largest wingspan of a modern bird is the albatross, at 3.5 meters, or 11 feet.

Fossil remains of a late Cretaceous pterosaur found in Romania were described in 2002 with the genus name Hatzegopteryx, but there is a lot of opinion among researchers that it may be identical with Quetzalcoatlus. It had a similar wingspan.

Because these fossils are quite fragmentary, it has been challenging to estimate the body weight of these huge pterosaurs. Some researchers speculate that they could not in fact fly, though I gather that that is a minority view. There’s even more debate about their mode of feeding. Some ideas suggest that they were skimmers, snagging fish out of the near surface of waterways and oceans, but others include the idea that they were actually quadrupedal on land. Most pterosaurs were. The bones of their wings, essentially their front legs, were strong enough for them to lumber around, and perhaps they did that as they scavenged land-based life. Arguments have been put forth against both the fish-eating and the scavenging modes of feeding, and a 2008 study suggests that they were terrestrial stalkers, preying on small land animals as modern storks do – bur remember that storks and other birds have no close affinities with pterosaurs – they just maybe occupy similar ecological niches.

—Richard I. Gibson

Drawing of Quetzalcoatlus feeding by Mark Witton and Darren Naish, used under Creative Commons license.