Scientists have long puzzled over how pterosaurs became the first vertebrates to master flight. Some pterosaur species, such as the Quetzalcoatlus were the largest known animals to ever take to the skies, with wingspans of over ten meters (on par with military aircraft like the Spitfire). My team’s new study may help solve the evolutionary mystery, revealing how a vane on the tip of their tails may have helped these ancient animals fly more efficiently.
It took some time for active flight to evolve in the natural world. The first flying animals were insects similar to dragonflies, which flapped their wings over swampy forests of the Carboniferous period (over 300 million years ago). Around 100 million years later (in a period known as the Triassic), the first bony animals, vertebrates, took to the skies. These vertebrates were pterosaurs, which dominated the skies of the Mesozoic era som 251-66 million years ago, swooping over the heads of dinosaurs.
Pterosaurs were unlike any animal known today. Imagine a flying squirrel hybridised with a lizard. All known members of this animal group order went extinct 66 million years ago and left no surviving descendants.
Their wings were made of a dynamic membrane hoisted on an elongated fourth finger and were probably covered in a fur-like outer protective layer. You might think it’s difficult to know what animals predating humanity by hundreds of millions of years looked like. And yet, technology can help us travel back in time and figuratively put flesh on the bones of extinct animals.
Our research used a new technology, Laser Stimulated Fluorescence (LSF), which helps us to see fossilised tissues invisible to the human eye. The laser stimulates different minerals and chemical traces in the fossil, making it emit colourful fluorescence and stand out against the grey rock it is encased in. It can reveal claws, beaks, skin, feathers, even delicate toepads of animals like dinosaurs that otherwise would be invisible. The final image looks like a photograph of a Jurassic roadkill.
Our team of palaeontologists from the University of Edinburgh and the Chinese University of Hong Kong collected pterosaur fossils held in museums (such as the Natural History Museum in London or the National Museum of Scotland in Edinburgh) and photographed them in darkrooms, capturing the long exposure under the laser.
To our surprise, detailed images of tail membranes popped out in a handful of specimens, along with a lattice of supporting structures, never seen before. The pterosaurs we studied come from the same species, Rhamphorhynchus. Rhamphorhynchus was a moderately sized pterosaur, on par, if not a tad smaller than a modern albatross. It had a slender beaked jaw filled with needle-like interlocking teeth, perfect for squid-snatching. It soared above the lagoons of Jurassic Central Europe almost 150 million years ago.
Birds flapped into existence sometime in the Jurassic, tens of million years later than the first pterosaurs (around 130 millions of years ago). Bats were last to the race. These flying mammals took flight after dinosaur demise, appearing in the Eocene epoch, 50 million years ago.
Most flying vertebrates evolved shorter bony tails as they took to the skies. Early pterosaurs differed from other flying animals, as they sported long, thin, bony tails with a paddle-like “vane” that changed shape depending on the species and age of the animal. For example, in the early pterosaur Rhamphorhynchus, baby specimens have teardrop-shaped tail vanes. In their teenage years the vane took a kite-like shape and in adulthood it resembles a triangular heart.
The specimens studied in our research had a kite-shaped tail vane, which was filled with intersecting structures, resembling ribs and spars in an aeroplane wing. The internal lattice could have allowed the membrane to dynamically tense up, like sail on a ship, and limit flutter that would hinder flight performance.
As pterosaurs evolved and became lighter and larger, their tails got smaller, and eventually disappeared.
Understanding the tail function can help us understand the evolution of flight, which in turn can inspire future technologies, such as planes, drones, even tent design. We can also learn about the behaviour and appearance of animals we will never be able to observe alive.
Pterosaurs were pioneers of flight, forever gone in a mass extinction. It is possible pterosaurs had many flight-aiding adaptations, which, in the fossil record, are invisible to the human eye. But with evolving technologies like the LSF we might find more clues to their aerial success and appearance. We now can see how this extinct creature could look like, live and function. A safer version of the Jurassic Park movies.
Natalia Jagielska received funding from NERC, as part of the E4 doctoral training program at the University of Edinburgh, which facilitated this research. The research was done with Thomas G Kaye of Foundation for Scientific Advancement, Sierra Vista; Michael B Habib of Department of Medicine, University of California Los Angeles; Tatsuya Hirasawa of Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, and Michael Pittman of The Chinese University of Hong Kong, Hong Kong SAR.
