Written by Prof Michael Benton, Palaeobiology Research Group, University of Bristol.
A new study (Yang et al. 2019) shows that pterosaurs, as well as dinosaurs had feathers, thus extending the origin of feathers minimally back to about 250 million years ago. Archaeopteryx, pretty much the oldest bird, dates from 150 million years ago, so that’s a backward jump of 100 million years. We’ve been creeping toward the realisation that feathers are not unique to birds for some time, but the new backwards shift comes as a shock!
For a long time of course, Archaeopteryx was the oldest bird, and the oldest fossil of any kind that showed feathers. Then, the Chinese Jehol fossils burst on the scene in the 1990s, and they showed feathers of one kind or another were present in many theropod dinosaurs, all close to the origin of birds. Then, feathers (or feather-like structures) were reported from ornithischian dinosaurs, and now, this year, in pterosaurs.
But are they really feathers? Palaeontologists have known that pterosaurs had a covering of whiskers of some kind, later called pycnofibres, as insulation to enable them to be warm-blooded. Our new find is that there are as many as four types of pycnofibres in a couple of pterosaur specimens from the Middle Jurassic of China, and some of these show branching. The dictionary definition of a feather is that it is an epidermal appendage showing branching (to distinguish it from mammalian fur which does not show branching). Do we follow this, or do we keep a set of differential terms for these structures in different beasts?
Maybe the name doesn’t matter- it seems most parsimonious to assume feathers arose once only, at the base of Pterosauria-Dinosauria, the clade called Avemetatarsalia. This places their origin in the Early Triassic, when life was recovering from the end-Permian mass extinction. Everything else was in place – the dinosaur line (archosaurs) and mammal line (synapsids) were diversifying and competing – the synapsids had hair and warm bloodedness, and the dinosaur ancestors were also warm-blooded, as shown by bone histology. They were all walking upright, instead of sprawling, and they had bird-like efficient respiration – so why not feathers too?
This study is part of a revolution in palaeontology that has happened in the past 30 years when methods (e.g. geochemistry, microscopy, computation) have crept into all branches (biostratigraphy, palaeontology, phylogeny, macroevolution), and speculation has been replaced by science.
Note from the Blog Editor:
The incredible discoveries outlined above are detailed in Mike Benton’s new book The Dinosaurs Rediscovered; How a Scientific Revolution is Rewriting History. This book, published April 2019, is available now. The Dinosaurs Rediscovered will be reviewed in an upcoming article on the GCG website.