PLAIN LANGUAGE SUMMARY:

Colouration rarely survives in fossils, as fossilisation processes usually destroy any colouration present in the organism during life. In exceptional circumstances, however, colour patterns are preserved on the surface of fossil shells as brown or black markings. The survival of fossils with their original colouration preserved, as described in this paper, is even more unusual. In this case over 78% of the shells of the brachiopod Calloria inconspicua from an 80,000 year-old Pleistocene locality in New Zealand show traces of their original red shell colouration. These fossils lived on boulders in a very shallow marine habitat. The species is still living in New Zealand, and an investigation of a modern population from an intertidal habitat indicates that such a high proportion of colour survival is unusual. Only 57% of 281 recently deceased individuals collected from the sediment surface beneath this modern population retained any shell colour, and this proportion dropped to 46% of the 321 shells found in the top 50 mm of sediment. Other fossil shells at the Late Pleistocene locality also revealed traces of preserved colouration, indicating that preservational conditions must favour the survival of shell colouration. The colouration of Calloria inconspicua is caused by a caroteno-protein, a bright red molecule formed from a protein attached to one or more brightly colored carotenoids (the molecules responsible for the colour of tomatoes and carrots). The caroteno-protein is embedded within the shell of Calloria inconspicua, and these types of molecules are known to be susceptible to degradation in the presence of light and oxygen. It seems likely, therefore, that the fossil shells were buried very rapidly in such a way as to exclude long-term exposure to oxygen, light, and other degradational agents. Detecting colouration in the remains of ancient organisms has considerable palaeo-biological significance, providing information on how these ancient organisms lived, how they interacted with other organisms, and how they evolved. Colouration of the shell may help warn off predators or camouflage the brachiopod; the same colouration in the free-swimming larvae may offer protection from UV-radiation, which can damage DNA.

Gordon B. Curry, Division of Earth Sciences, Gregory Building, University of Glasgow, Glasgow, G12 8QQ, Scotland (G.Curry@earthsci.gla.ac.uk)