October 12. Jurassic pterosaurs

Pterosaurs, whose name means “winged lizards,” began during the Triassic but really took off during the Jurassic. They were the first vertebrates to attain true flight, and while they are often called flying dinosaurs, they are not closely related to either dinosaurs or birds. Their descent within the reptiles is ultimately from some basal archosaur, but because of poor and sporadic preservation, their ancestry is not well understood. 

The wing-flap in pterosaurs was stretched over a greatly extended fourth finger. Bats, in contrast, have all their digits extended. 

Rhamphorhynchus image source: Picture by M0tty or Antoine Motte dit Falisse, used under Creative Commons license.

Rhamphorhynchus was an exclusively Jurassic pterosaur that grew to have a wingspan of about two to three feet, with a diamond-shaped tail appendage that might have served as a rudder. The name means beak-snout, and that snout was full of teeth. Spectacular examples have been found in the Solenhofen Limestone of Germany that preserve the soft tissues including the wings. Although it might seem that an active flying animal like rhamphorhynchus would have been warm-blooded, this is not established, and some lines of reasoning, including a slow growth rate to adulthood, something like three years, argue for a cold-blooded metabolism. This may not have been true of all the pterosaurs, however.

There are more than 30 different genera of Jurassic pterosaurs, so they were quite diverse. Most were relatively small, with wingspans of a few feet. There’s been a lot of analysis to try to separate small pterosaurs from juvenile versions of larger species, and there probably were some pretty small pterosaurs, the size of small birds like sparrows.

Geographically, Jurassic pterosaurs have been found on every continent, although they are quite rare in Australia and Antarctica – but whether that is a measure of their distribution or lack of appropriate sediments to preserve their fossils is unclear.

Next month, the Cretaceous, we’ll revisit pterosaurs because that’s when they became gigantic, the largest flying animals in earth’s long history.

If you are in New York, there is an exhibit at the American Museum of Natural History on pterosaurs. It runs through January 4, 2015.

—Richard I. Gibson

LINKS:
Pterosaur skeleton
Rhamphorynchus life story
AMNH Exhibit 

Rhamphorhynchus image source: Picture by M0tty or Antoine Motte dit Falisse, used under Creative Commons license.