Evolutionary link that helped pterosaurs fly

It’s taking time – in no small part due to the difficulty in finding good evidence – but we’re slowly learning more about the back story of pterosaurs, the first vertebrates to evolve powered flight.

Just a few weeks back, Cosmos reported on research showing that the winged cousins of dinosaurs got better and better at flying throughout their existence.

Now a new paper in the journal Nature suggests that their closest evolutionary relatives were a group of small, flightless dinosaur-like animals known as lagerpetids.

An international team led by Martín Ezcurra from Museo Argentino de Ciencias Naturales in Buenos Aires used micro-computed tomography scans and 3D reconstructions to analyse skulls and skeletons recently unearthed in North America, Brazil, Argentina and Madagascar, revealing similarities in pterosaur and lagerpetid anatomy.

“CT data has been revolutionary for palaeontology,” says co-author Michelle Stocker, from Virginia Tech, US. “Some of these delicate fossils were collected nearly 80 years ago, and rather than destructively cutting into this first known skull of Dromomeron, we were able to use this technology to carefully reconstruct the brain and inner ear anatomy…”.

One stark revelation was that the flightless lagerpetids had evolved some of the neuroanatomical features that allowed the pterosaurs to fly, including characteristics of their braincase and inner ear, and similarly elongated palm bones.

The researchers used an approach called phylogenetic systematics, which, as Kevin Padian from the University of California, Berkeley, explains in an associated commentary in Nature, has been applied to uncover relationships between “every group of organisms”.

“It searches out newly evolved features that link different organisms, the reasoning for this being that the most recently evolved traits must have appeared in forms most recently diverged from each other, and hence must be the closest genetically,” he writes.

“These features, which often seem trivial even to experienced observers, provide the key to relationships, and sometimes to the evolution of adaptations, because one divergent group, the flying pterosaurs in this case, might have unusual features that reflect functions its sister divergent group lacks.”

Ezcurra and colleagues suggest their findings could provide a completely new framework for studying pterosaurs. Some palaeontologists have attributed their unique body plan to fast evolution, but if lagerpetids are deemed their precursors, and thus a “middleman” of sorts, pterosaurs likely evolved at the same rate as other major reptile groups.

“Flight is such a fascinating behaviour, and it evolved multiple times during Earth’s history,” says co-author Serjoscha Evers, of the University of Fribourg, Switzerland. “Proposing a new hypothesis of their relationships with other extinct animals is a major step forward in understanding the origins of pterosaur flight.”