The ‘Sword Tail from Bavaria’: fossil helps researchers piece together Pterosaur evolution

An exceptionally preserved fossil of a new species of pterosaur, Skiphosoura bavarica, fills a gap in the understanding of the evolution of these ancient flying reptiles. The study, recently published in the journal Current Biology, provides crucial insights into how pterosaurs transitioned from smaller, long-tailed forms to the massive, short-tailed giants of the Cretaceous period.

The finding was reported by Discover Magazine, Science Daily, IFLScience, and Deutche Welle, among others.

Discovered in 2015 in a limestone quarry in Solnhofen, Bavaria, the fossil represents a nearly complete skeleton of Skiphosoura bavarica, or "sword tail from Bavaria." This name reflects its distinctive short, stiff, and pointed tail—a key feature that distinguishes it from both its predecessors and successors. The fossil's remarkable three-dimensional preservation has allowed scientists to examine its anatomical features in unprecedented detail, revealing crucial steps in pterosaur evolution.

David Hone, co-author of the study from Queen Mary University of London, expressed the significance of the find: "This is an incredible find. It really helps us piece together how these amazing flying animals lived and evolved. Hopefully, this study will be the basis for more work in the future on this important evolutionary transition."

Skiphosoura bavarica lived toward the end of the Jurassic Period and would have been one of the largest flyers in its ecosystem, measuring about two meters long with a wingspan of 1.75 meters. This size is substantially larger than most of its pterodactyl predecessors and is similar to the dimensions of large birds like the golden eagle. Its metacarpal bones are considerably longer than those of earlier pterosaurs, though not fully matching those of pterodactyloids, indicating important anatomical differences.

The fossil reveals that Skiphosoura bavarica is anatomically transitional between the long-tailed, relatively small pterosaurs of the Triassic period and the short-tailed giants like Quetzalcoatlus from the Cretaceous. It retains characteristics of late pterosaurs, such as a long head and neck, but features a shorter tail and fingers. This combination of traits suggests that evolutionary changes occurred gradually and complexly.

Paleontologists have long distinguished between two main groups of pterosaurs: the earlier long-tailed forms known as non-pterodactyloids and the later, much larger pterodactyloids with short tails. However, the evolutionary steps between these groups remained unclear due to a fragmentary fossil record. The discovery of transitional species like Skiphosoura bavarica and the earlier-found darwinopterans has begun to fill this gap.

Adam Fitch, a paleontologist and co-author of the study from the University of Wisconsin-Madison, emphasized the importance of Skiphosoura in understanding pterosaur evolution: "Skiphosoura represents an important new form for working out pterosaur evolutionary relationships and by extension how this lineage arose and changed."

The fossil record of pterosaurs is limited due to their lightweight bones, which fossilized imperfectly. Most specimens are flattened and shattered, complicating the study of their evolution. The exceptional preservation of Skiphosoura bavarica provides valuable evidence of the gradual anatomical changes that occurred over millions of years.

Pterosaurs were the first vertebrates to achieve powered flight, appearing about 228 million years ago and becoming extinct 66 million years ago in the mass extinction event that also doomed the dinosaurs. They exhibited great diversity in sizes and shapes, ranging from small species the size of modern birds to massive species like Quetzalcoatlus, which had wingspans of up to 13 meters.

David Hone noted the challenges in studying pterosaur fossils: "Pterosaur skeletons are really fragile; because their bones are very thin, they often break apart or get crushed when preserved." The well-preserved state of Skiphosoura bavarica offers a rare opportunity to study these creatures in detail.

The discovery also highlighted the evolutionary process within pterosaurs. Skiphosoura bavarica shows modifications in wing bone ratios and a shorter fifth toe, traits that are not as extreme as those seen in pterodactyloids but indicate significant evolutionary steps. The changes suggest increasing terrestrial competence and the beginnings of adaptations that would allow later pterosaurs to reach enormous sizes.

Furthermore, the pterosaur's teeth are quite long and sharp, designed for puncturing and holding prey. "The teeth are quite long and sharp. They are for puncturing and holding," David Hone said. This suggests that Skiphosoura bavarica was probably a generalist predator of small prey such as lizards, small mammals, large insects, and perhaps fish. It likely lived inland, perhaps in forests, rather than in coastal environments like many other pterosaurs.

The fossil was prepared by experts who recognized its significance. Stefan Selzer, an author on the project who prepared the specimen, said: "As a preparator I have worked on more than 60 pterosaur specimens from Solnhofen limestone. I recognized during the final prep this specimen showed features that combined characteristics of both major groups of pterosaurs, with the shortened tail as the most important diagnostic feature."

The findings contribute significantly to the reconstruction of the pterosaur evolutionary family tree, illustrating how physical traits gradually evolved, including the increase in size of the head and neck, elongation of wrist bones, and reduction in finger and tail length. This sequence shows that evolutionary transitions occur gradually and complexly, filling in previously unknown steps in the evolution of these remarkable flying reptiles.

Dr. David Hone concluded: "It really helps us find out how these amazing creatures lived and evolved. Hopefully, this study will be the basis for more work in the future on this important evolutionary transition."

This article was written in collaboration with generative AI company Alchemiq