From which beings did the first flying vertebrates evolve? Paleontologists have now come an important step closer to solving this old riddle: They have identified the so-called Lagerpetidae as primeval relatives of the pterosaurs. The insights into the anatomy of these two-legged lizards provide clues about the physique that formed the basis of the development of the pterosaur design. Many aspects of the evolutionary history of the primeval rulers of the skies, however, remain mysterious, the paleontologists emphasize.
Long before the first birds or bats swung their wings, the pterosaurs had already developed the ability to actively fly. Up to their violent end after the asteroid impact about 66 million years ago, these pioneers in animal aviation were extremely successful: In the course of their 150 million year history of development, the pterosaurs produced many highly developed species and subgroups that are similar to today’s birds had adapted to different ways of life. Among them were sparrow-sized flight artists but also the tallest creatures that have ever soared into the air – some pterosaurs reached a wingspan of over ten meters.
But what kind of animals were they? What is clear is that they were not representatives of the dinosaurs – both groups of animals only had common ancestors. The question of which ancestors the pterosaurs could have emerged from has occupied paleontologists for around 200 years. The problem: So far, no transitional forms have been found – the pterosaurs seem to have fallen from the sky. The oldest known representatives from the Triassic era already had highly specialized adaptations of their bodies to flying. This very special anatomy created a large morphological gap between the pterosaurs and all other known reptiles from the era of their origin.
Looking for relatives
As long as there are no finds of clear transitional forms, therefore, only more fundamental insights into the family relationships can provide clues to the origins of the pterosaurs, explains the international research team. But there were still unanswered questions. “We think we’ve found the answers now,” says co-author Sterling Nesbitt of the Virginia Polytechnic Institute and State University in Blacksburg. The scientists focus on a certain group of dinosaurs as the closest primeval relatives of the pterosaurs: the Lagerpetidae. They were small, wingless reptiles that are known from 237 to 210 million years ago. Previous research on the remains of these animals has shown that the length and shape of their bones were similar to those of pterosaurs and dinosaurs. But until now it was assumed that the Lagerpetidae were closer to the dinosaurs.
However, as the scientists are now reporting, new findings from representatives of these animals and more precise results of investigations into their body structures now give a different picture. With the help of micro-computed tomography (μCT) scans to reconstruct fine structures in newly discovered and already known fossils, the paleontologists found that the characteristics of the Lagerpetidae were very similar to those of pterosaurs. The researchers therefore come to the conclusion that the Lagerpetidae belonged to the group of precursors of the pterosaurs and thus probably possessed basic characteristics from which the adaptations to flying later emerged.
Fine but clear similarities
Thanks to the non-destructive examinations using micro-computer tomography, the researchers were able to reconstruct the anatomy of the brain and the inner ear in detail and compare them with the characteristics of other fossils. The results suggest that the flightless Lagerpetidae already possessed some of the neuroanatomical features that later enabled the pterosaurs to fly. Given the little information paleontologists previously had about the early pterosaurs, they had often assumed extremely rapid evolution in acquiring the unique adaptations. But the new findings on the Lagerpetidae now suggest that the pterosaurs also evolved at a rate similar to other large groups of reptiles, say the scientists.
But as they emphasize, many questions still remain unanswered: The knowledge that the Lagerpetidae were close relatives of the pterosaurs still does not clarify how they brought about their main characteristic: “We lack information about the earliest pterosaurs, and it remains largely unclear, how changes in their skeletons have created flight animals, ”says Nesbitt. He and his colleagues now want to investigate the puzzle further. In a comment on the study, Kevin Padian of the University of California at Berkeley writes: “Perhaps one day an ancestor of the pterosaurs will emerge from the rocks of the Triassic, who can fill the gaps in knowledge about the evolution of these animals – similar to Archeopteryx in the case of the Evolutionary history of birds has done, ”said the paleontologist.
Source: Virginia Polytechnic Institute and State Universit, Article: Nature, doi: 10.1038 / s41586-020-3011-4