Pterosaurs were a diverse group of flying reptiles in the Mesozoic who at one point, underwent a whole body plan reorganization, with later forms completely replacing earlier ones. These anatomical redesigns resulted in the origin of Pterodactyloidea, a highly specialized group containing the largest flying creatures ever known.
Now, scientists working in northwest China have discovered the earliest known pterosaur with diagnostic characteristics of pterodactyloids. This basalmost (or primitive) pterodactyloid pterosaur was flying overhead 163 million years ago -- which extends the fossil record of advanced pterosaurs by at least five million years to the Middle-Upper Jurassic boundary. They suggest naming Kryptodrakon progenitor.
The fossil fragments of the small pterodactyloid -- with a wingspan of 1.4 meters -- was found in 2001 in a mudstone of the Shishugou Formation. The quicksand in the area trapped a range of prehistoric animals (including tyrannosaurs), stacking them one on top of the other. It’s known as the "dinosaur death pits.” Kryptodrakon was found 35 meters below an ash bed that’s been dated to more than 161 million years.
An international team led by Brian Andres from the University of South Florida focused on one of the metacarpel (or palm) bones, which is longer than those found in its more primitive relatives. “In primitive pterosaurs, it is one of the shortest and least variable bones in the wing, but in pterodactyloids it is quite elongated," Andres tells Reuters. "We can look at his anatomy and see what were the last changes in his body that may be responsible for the success of the group.” Pterodactyloidea includes Quetzalcoatlus, for example, which had the wingspan of an F-16 fighter.
Pterosaurs supported their wings with a long fourth digit (basically their pinky finger). As the pterosaurs evolved, their wings changed shapes. Narrow wings were useful for marine environments, and broader wings offered more control for navigating challenging land environments. Advanced pterosaur specimens have mostly been found in prehistoric marine settings; not surprising, since the oceans were teeming with life (and food). But Kryptodrakon was surprisingly terrestrial -- flying above floodplains and seashores -- suggesting how pterodactyloids actually evolved in inland settings.
“He fills in a very important gap in the history of pterosaurs,” Andres says in a news release. “With him, they could walk and fly in whole new ways.” Here are the bones, each pictured from multiple angles.
The name comes from “Krypto” for hidden and “drakon” for serpent, referring to “Crouching Tiger, Hidden Dragon,” which was filmed near the area (now a desert) where the species was discovered. And “progenitor,” meaning ancestral or first-born, refers to its status as the earliest pterodactyloid. The specimen is housed at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing.
This new take on the evolution of pterosaurs is supported by correlations between wing shape and the environment in pterosaurs as well as modern flying vertebrates, like bats and birds (who showed up 50 million years later). Pterosaurs are not the ancestors of modern birds. Those of course, would be the dinosaurs.
The work was published in Current Biology this week.