New fossil reveals the evolution of flying reptiles

Nov. 18 () –

A new species of pterosaur that helps explain the evolution of flying reptiles has been described in ‘Current Biology’ by paleontologist David Hone of Queen Mary University of London.

Pterosaurs are extinct flying reptiles that lived alongside their close relatives, the dinosaurs. The largest of them reached 10 m in wingspan, but primitive forms were generally limited to about 2 meters.

The animal was named Skiphosoura bavarica, which means “Bavarian swordtail”, because it comes from southern Germany and has a very unusual short, stiff and pointed tail. The specimen is complete and retains almost all bones and, unusually, is preserved in three dimensions, where most pterosaurs tend to flatten. In life, it would have had a wingspan of about 2 meters, similar to that of large birds such as the golden eagle.

For two hundred years, paleontologists divided pterosaurs into two main groups: the early non-pterodactyloids and the later, much larger ones. Early pterosaurs had short heads on short necks, a short wing wrist bone, a long fifth toe, and long tails, and pterodactyloids had the opposite: large heads on long necks, a long wrist, a fifth toe short and a short tail. But it was not known which parts of their bodies changed in each of these groups.

In the 2010s, a series of intermediate species called Darwinoptera were discovered, revealing that the head and neck had changed before the rest of the body. It was a great example of an intermission that closed an evolutionary gap, but it also meant that we didn’t really know what was happening before or after these changes.

Skiphosoura reveals these changes. Evolutionarily it is situated between these primitive Darwinoptera and the pterodactyloids. It retains a head and neck very similar to those of pterodactyloids, but also shows a longer wrist and a shorter toe and tail than early Darwinoptera, although these are not as extreme as those observed in pterodactyloids. With the study also comes a new reconstruction of the evolutionary family tree of pterosaurs. In addition to showing the intermediate position of Skiphosoura, it also shows that a Scottish pterosaur, Dearc, fits into the mirror position between primitive pterosaurs and early Darwinoptera.

In other words, a complete sequence of evolution from the first pterosaurs to Dearc, the first Darwinoptera, Skiphosoura and the pterodactyloids is now available. While not all specimens are complete, we can now trace the increase in head and neck size, elongation of the wrist, shrinkage of the fingers and tail, and other characteristics step by step in various groups. It’s an excellent illustration of the evolution of a group for which the transition has been far from clear until now.

Both Dearc and Skiphosoura are unusually large for their time, which also suggests that the changes that allowed pterodactyls to reach enormous sizes appeared even in these transitional species.

David Hone, from Queen Mary University of London, concludes: “It’s an incredible find. It really helps us piece together how these amazing flying animals lived and evolved. “We hope this study will be the basis for more future work on this important evolutionary transition.”