Tuesday, 29 April 2014

Ancient Wings, Ancient Skies

Pterosaurs dominated the skies before
their extinction 65 million years ago
Pterosaurs are the only known group of reptiles to conquer the skies. While lizards, today and hundreds of millions of years ago, had the ability to glide through the air. Only the pterosaurs possessed powered flight, enabling them to travel vast distances on the wing.

Some specimens were minute, barely a few centimetres from nose to tail. Others were vast. While a few incredible beasts rivaled light aircraft in wingspan. The pterosaurs perished along with the dinosaurs 65 million years ago, yet were hugely diverse. Now a discovery from China shows just how long they existed as masters of the skies.

In 2001 a pterosaur specimen was uncovered in the so-called 'dinosaur death pits' of the Shishugou Formation in north west China; preserved in quicksand was an early tyrannosaurid. It was housed in the Institute for Vertebrate Palaeontology and Palaeoanthropology for some years before it was rediscovered and analysed by Dr Brian Andres from the University of South Florida, James Clark from the GW Columbian College of Arts and Sciences and Xu Xing from the Chinese Academy of Sciences. Their findings were remarkable.

The tyrannosaurid's morphology was incredibly primitive, barely placing it within the pterosaur family. The specimen came from a layer 35 metres below an ash bed which had been dated to 161 million years old. The specimen must therefore have been at least as old, although the true date is probably around 163 million years old; five million years older than any previously described species. This suggests it was an early member of the pterosaur family, perhaps lying close to their evolutionary origin. 

The 163 million year old fossils of Kryptodrakon progenitor
Andres, Clark and Xing gave it the name of Kryptodrakon progenitor. The name translates as 'hidden dragon' honouring the film Crouching Tiger, Hidden Dragon filmed a few miles from its discovery. Progenitor simply references its place in the evolutionary history of pterosaurs. 'He (Kryptodrakon progenitor) fills in a very important gap in the history of pterosaurs,' Dr. Andres said. 'With him, they could walk and fly in whole new ways.' 

'Kryptodrakon is the second pterosaur species we've discovered in the Shishugou Formation and deepens our understanding of this unusually diverse Jurassic ecosystem,' added Dr. Clark. 'It is rare for small, delicate fossils to be preserved in Jurassic terrestrial deposits, and the Shishugou fauna is giving us a glimpse of what lived alongside behemoths like Mamenchisaurus.'

The Shishugou Formation, composed of sands and sediments, once formed a floodplain, hence the treacherous quicksands. Kryptondrakon would have fed on fish and perhaps arthropods. Yet it is the shape of the wing that is of interest. Unlike other pterosaurs which inhabited aquatic or marine biomes, Kryptodrakon had quite wide wings, making it similar to terrestrial forms. This suggests that the group evolved in inland environments. Indeed this would make sense if powered flight developed from reptiles using enlarged forearms for gliding between trees.

If this is the case then its implications are great. It is thought that birds evolved from small arboreal dinosaurs who used feathered forearms as a means of gliding. A tree-based flight-origin in two of the four groups of organisms who have developed powered flight, would suggest that a similar origin is not unfeasible for the other two, namely bats and insects. How these groups developed flight is unclear. Understanding the origins of flight in other groups of aerial organisms, such as the pterosaurs, impacts on how bats and insects may have reached for the skies.