Reptile grew feather-like structures before dinosaurs
FOSSIL feathers provided the definitive proof that birds descended from dinosaurs. There is one extinct beast that doesn’t fit the picture, though. It is called Longisquama insignis, and it lived 230 to 240 million years ago – just before the dinosaurs evolved, and 70 to 80 million years before the first fossils of feathered dinobirds. Why, then, did Longisquama sport what look suspiciously like feathers?
Some palaeontologists think that it didn’t: they say that the only known specimen of Longisquama – found in Kyrgyzstan in the 1960s and shown here at life size – was just a run-of-the-mill reptile that died beneath some exotic plant fronds, so the “feathers” were not actually part of the animal. A small group of researchers say Longisquama‘s feathers are real, and suggest that birds evolved from reptiles like this rather than from feathered dinosaurs. A new analysis suggests neither theory is correct.
“The strange skin appendages of Longisquama are neither scales nor feathers,” says Michael Buchwitz of the Freiberg University of Mining and Technology, Germany. “They are perhaps linked to the early evolution of dino and pterosaur fuzz, though.”
Buchwitz has reanalysed the original fossil and says that the base of the structures lies so close to the bones of the spine that they were probably anchored deep within the skin. They were definitely attached to the body.
He has also studied recently discovered isolated “feathers” from the same locality, which are better preserved. He says Longisquama‘s appendages neither branch like real feathers nor vary in structure along their length as feathers do. Most tellingly, each carries a very unfeather-like thick border along one edge.
For all that, Buchwitz says the appendages are clearly similar to the real deal. Like feathers, they have a central filament running along their lengths, for example. He thinks this means that they were constructed using the same developmental genes that later produced feathers.
Longisquama‘s skeleton is too incomplete to work out its exact evolutionary position, but Buchwitz says the little reptile was probably part of the lineage that gave rise to pterosaurs, crocodiles, dinosaurs and birds. Many of these groups later evolved their own skin appendages, including filaments on pterosaur wings, quills on the tails of some plant-eating ornithischian dinosaurs, and the proto-feathers of theropod dinosaurs. Longisquama shows that evolution was experimenting with the genes that gave rise to feathers long before any of these animals appeared on the scene.
“It’s a very impressive analysis,” says Alan Brush, a feather specialist at the University of Connecticut in Storrs.
Larry Martin at the University of Kansas in Lawrence is one of the few researchers who think Longisquama-like reptiles gave rise to birds. He likes the idea that its appendages developed along similar lines to feathers. For most palaeontologists, though, Longisquama is an intriguing evolutionary experiment that apparently left no descendants.
23 March 2012 New Scientist – by Jeff Hecht