A 4-cm piece of amber discovered among thousands of others in a quarry from southwestern France is helping to bridge a gap in our knowledge of the early development of feathers. The amber dates from the Early Cretaceous period, around 100 million years ago, and encases at least seven beautifully preserved feathers of a primitive type never seen before. They represent a critical stage in the evolution of feathers.

Conventional imaging techniques using transmitted light microscopes were used first (Figure 144) but this did not reveal sufficient information for a precise assessement of the morphology of the feathers. Phase contrast X-ray synchrotron imaging techniques have already demonstrated their power on fossil inclusions in amber [1], so we decided to apply such methods to image the unique fossil feathers. To reveal the finest structures of the feathers in three dimensions, a mosaic of 6 scans was performed using a single-distance phase retrieval approach (holotomography) with a voxel size of 0.7 micrometres, at beamline ID19. Complex multistep data processing allowed an enhancement of the visibility of the feathers and other fine structure and then the virtual extraction of the most well-preserved feather from the resin.

Fig. 144: Fossil feathers preserved in a 100 million-year-old piece of amber from France, observed by transmitted light microscopy. Scale bar 0.1 mm.

Detailed holotomographic images (Figure 145) revealed a unique structure in the feathers morphology that was previously unknown. The fossils display a flattened primary shaft – or rachis – composed of the not-yet-fused bases of the secondary branches – or barbs – that initiate the planar form of later feathers. The barbs fuse progressively and lack the complete fusion that is observed in the rachis in all other fossil and modern feathers. The planar form of the fossil feathers was observed here for the first time. It results from the insertion of barbs on the two opposite sides of the shaft whose shape is flattened with respect to modern feathers.

This structure represents an intermediate and critical stage in the incremental evolution of feathers. It had been predicted by developmental theories [2] but was hitherto undocumented by evidence from the recent or the fossil record. Primitive and derived feathers occur in both early birds and some dinosaurs known as theropods. Interestingly, teeth from two species belonging to this group of feathered dinosaurs were found fossilised in the same quarry as the amber, raising the possibility that the feathers come from a dinosaur rather than a bird.

Fig. 145: 3D virtual reconstruction of the best-preserved fossil feather using holotomography: long filaments inserted parallel and opposite on each side of a flattened primary shaft initiate the planar form of later feathers.

In conclusion, the feathers’ primitive feature differs from all other known morphologies, both modern and fossilised. It provides evidence for a key step in the evolution of feathers leading towards feathers for the purpose of flight, thus in the transition between dinosaurs and birds.


Principal publication and authors

V. Perrichot (a), L. Marion (b), D. Néraudeau (c), R. Vullo (c), P. Tafforeau (d), Proc. Roy. Soc. B, 275, 1197 (2008).
(a) University of Kansas (USA)
(b) Ecobio, UMR 6553, Rennes (France)
(c) Géosciences Rennes, UMR 6118, Rennes (France)
(d) ESRF


[1] M. Lak et al., Microsc. Microanal., 14, 251 (2008).
[2] R.O. Prum and A.H. Brush, Q. Rev. Biol., 77, 261 (2002).