One hundred and fifty million years ago, the Solnhofen Limestones of Germany were covered in small islands and warm saltwater lagoons. Coral reefs flourished with crinoids, sponges, jellyfish, and crustaceans; Dragonflies buzzed above the water as small reptiles sunned themselves at the water’s edge. Pterosaurs and Archaeopteryx took to the skies, but there was trouble in this Jurassic paradise: Tropical storms would turn it into a pterosaur graveyard.
What paleontologist Rab Smyth found in this graveyard finally revealed why so many fledgling pterosaurs had succumbed to the storm. Smyth, a researcher at the Center for Paleobiology and Biosphere Evolution at the University of Leicester, unearthed two Pterodactylus antiquus hatchlings, and their bones showed exactly how they had succumbed to storm winds. The wings of both specimens (ironically named Lucky I and Lucky II) revealed clean, slanted humerus fractures that suggested they had been twisted in the storm. Unable to fly, they drowned and were rapidly buried in the lagoon depths.
“Our results show that most pterosaurs are preserved predominantly through catastrophic events, often reflecting mass mortality episodes,” Smyth and his research team said in a study he led, recently published in Current Biology.
Ancient autopsy
Solnhofen is a Lagerstätte, a region known for its exceptional preservation of fragile creatures that would have otherwise been lost to time. Anything that sank to the bottom of a lagoon was buried in soft carbonate muds that hardened into limestone over hundreds of millions of years. Many juvenile pterosaurs, thought to have been overpowered by storm winds before being plunged into the lagoons and covered in mud, had already surfaced at the site. What makes this new discovery so significant is that none of the previous finds showed any skeletal trauma.
Most of the pterosaur fossils found at Solnhofen are rather small. Long thought to belong to a smaller pterosaur species, they were later found to be juveniles of a larger species. That raises the question of how their delicate bones and soft tissues were preserved while larger casualties of the storm only left behind fragmented skeletons. Juveniles had hollow bones just like adults, but their bones were much more fragile and should not have held up easily under the weight of sediments. The expectation would be that the bodies of more robust adults would have stood a better chance of fossilization.