Re: paleonet Fossil Color

From

Date
Reply-To

Living organisms exhibit two main types of coloration: pigmentary and structural colours. Probably you realise what is a pigmentary color. A pigment, usually an organic component such as melanins (i.e. mammal’s skin and hair), carotenoids (i.e. astaxanthin in crayfish), bilins (i.e. bilverdin in bird eggs), quinines (i.e. echinoquinones in sea urchins), give some coloration as ink do it in a paper. Usually such pigments are in specific cells (chromatophores, melanophores, etc) scattered in particular tissues (dermis, epidermis, etc.).

On the other hand, structural colours are due to the microscopic features of the physical surfaces. These include interference, diffraction, reflection, refraction, iridescence… A very famous structural colour is the Tyndall blue (a similar phenomena to the Rayleigh scattering observed in Earth’s atmosphere). Nacre exhibits iridescent structural colour.

Animals combine any of such structural colours with pigments in a plethora of visual effects not only in the same estructure but also different parts of the organism are coloured using differnt "technologies". Usually, black or brownish colours are usually pigmentaries. However, white colour rarely is pygmentary .

Most of the pigments may well decay after death. However structural colours may be easily preserved, although as such colours depends of the very precise length of the micro-details of the surface (in terms of fraction of wavelength of incident light) the resulting colour after fossilization should be very different. For example, the beautiful metallic green of some of the Lucanids beetles from Messel, could be not green but dark violoaceous (for example). Other examples of structural coloration are the brownish pattern that some fossil moths and butterflies exhibit in their wings.

Jere Lipps proposes a couple of Ph.D. dissertation on colours. Possible candidates: don’t forget to use SEM to check the surfaces at wave length scale. Structural colours, although not visible today should be preserved in some way…

Cheers,

Patricio Domínguez

----- Mensaje original -----

De: "Jere H. Lipps" <jlipps@berkeley.edu>

Fecha: Martes, Junio 14, 2005 8:23 am

Asunto: Re: paleonet Fossil Color

> We need some studies on the taphonomy of color.
>
> My impression is that color is preserved in certain circumstances,
> including species-specific aspects. Organic rich and/or anoxic
> deposits seem to preserve color sometimes, whereas others (oxic?)
> do not. Certain gastropods seem to show more color whereas
> others have no color when alive. So a taphonomic review would run
> the entire gamut from living through fossilization to collection
> by paleontologists (do we pick out the colored ones more than
> others?).
> Probably a couple of Ph.D dissertations in this, at least. Maybe
> some have been done, but more could be done I'd bet.
>
> Jere