Baby pterosaurs likely died in violent Jurassic storms

The broken wings of two pterosaur hatchlings point to how hundreds of their kind may have met an untimely end. If true, this would solve a cold-case millions of years old.

New analyses focused on two complete fossils of the genus Pterodactylus. The specimens, dubbed “Lucky I” and “Lucky II,” show a clean humerus bone fracture in a wing on each. The diagonal-line breaks occurred as the flyers’ arms were wrenched in a powerful twisting motion.

Robert S. H. Smyth at the University of Leicester, in England, and his colleagues described the wing breaks in the October 6 Current Biology. A violent storm was the likely cause, they say. Its winds would have proved just too powerful for the fledgling reptiles.

The mass-pterosaur demise occurred roughly 150 million years. That’s when much of what’s now Germany was covered by a warm, shallow sea. Coral reefs walled off parts of that sea. This created isolated lagoons with thick, soft mud bottoms.

That carbon-rich mud was an ideal environment in which the fragile, lightweight bones of these reptiles — cousins of dinosaurs — could turn into fossils.

Over the eons, one such lagoon morphed into what’s now known as the Solnhofen limestone quarry. It’s filled with Jurassic Period fossils that include small dinos and Archaeopteryx (Ar-key-OP-tur-ix), the earliest known bird.

This ancient graveyard is known for its many pterosaur fossils — particularly those of hatchlings.

These fossils are now helping scientists better understand not only the growth of young pterosaurs, but also what they ate, and when and how they could fly.

Oddly, adult pterosaurs at this quarry tend to be found in fossil bits and pieces. In contrast, skeletal remains of younger individuals are beautifully complete. That would not seem to make sense: Skeletons of hatchlings should be more fragile than those of adults.

But strong storms could explain this mystery, Smyth’s team now says. Young pterosaurs likely would have struggled against violent winds. Many would ultimately fall into the lagoon where they drowned, the team suggests. In short order, the lagoon’s sediment would then have entombed their bones.

Older pterosaurs, in contrast, are more likely to have struggled mightily — both in the storms and the lagoon — before dying. Their carcasses may then have been tossed about in the water before sinking. The result: Their bones could scatter widely.

This new analysis, Smyth’s team says, highlights how catastrophic storms may affect the degree to which different-age specimens are preserved. In this way, they note, weather can distort the fossil record.