Fossil Shells With Color Patterns

[DPS Ammonite]

 

 

While researching what caused the current invertebrate fossil of the month to have such a wonderful iridescence (www.thefossilforum.com), I came across some interesting info on preservation of color patterns in fossil shells. In Northern California where I live, most of the color of a fossil shell disappears after a few thousand years. The pattern of color is gone in a couple million years. While in Texas, I collected Texigryphea from the early Cretaceous that still had color patterns of dark radial bands. Finding a paper about Devonian brachiopods with color patterns surprised me. See: http://www.bioone.org/doi/full/10.4202/app.2010.0066 “First Colour-Patterned Strophomenide Brachiopod from the Earliest Devonian of Podolia, Ukraine” by Andrzej Baliński, found in Acta Palaeontologica Polonica 55(4):695-700. 2010.

 

The first figure below shows the spotted pattern found on the convex shell of a strophomenid brachiopod from Ukraine. Wow, what a camouflage! The brachiopods blended right in against the light-colored rock with dark spots. I am reminded of well camouflaged modern mottled and spotted moths that are hard to see when they are on certain trees and rocks.

 

The second figure shows a variety of color patterns found in fossil brachiopods. The paper suggests that brachiopods with colors and patterns occur in shallow water in the photic zone and in areas with warmer water. Few are found in cold polar waters. A similar distribution of colored shells and mollusks exists today. Shallow tropical species are very colorful while polar and deep water species are not.

Show us some of your older fossil shells with colored patterns: Cretaceous and older.

 

 

 

 

 

 

[Fossildude19]

Thanks for posting this.  

Very interesting reading. 

Regards,

[Scylla]

As soon as I find one older than cretaceous with color, I will! Some colors that we cannot see are being discerned by ultrastructural studies looking at microscopic details that indicate color such as putative melanosomes, etc. I have seen some trilobites with color as well, but I don't have any in my collection.

[FossilDAWG]

Sometimes color patterns can be seen if you use UV light, even if the shell looks completely bleached in visible light.  Also keep in mind that the pattern could be due to remaining traces of the original pigment molecules, but it could be also be to traces of breakdown products of those molecules (due to oxidation or polymerization for example), or (especially in older fossils) differential mineralization of the shell.  It may be possible to infer the pattern of color from such specimens, but you cannot assume you are seeing the original color.

 

I know of several Cretaceous sites in Alabama where some shells, especially oysters such as Pycnodonte, clearly retain obvious color patterns.  I have also seen Ordovician cephalopods with color markings.  Some of those were silicified, and when the shells were etched from the limestone matrix with acid you could see the color bands and longitudinal markings reflected in less completely silicified regions of the shell, which is consistent with a different mineral composition.

 

Don

[tmaier]

"when the shells were etched from the limestone matrix with acid you could see the color bands and longitudinal markings reflected in less completely silicified regions of the shell, which is consistent with a different mineral composition. "

I've seen that in Plio-Pleistocene shells. The areas that should have color often have a different consistancy than other areas, such as a difference in microscopic porosity or density.

Bleaching these shells enhances this difference in properties, creating more contrast, and you can see where there were patterns. I was thinking that a dye might have a differential attraction to these two different surfaces, and also show the patterns. You don't know what the old color was, but you know some of the pattern that was there.

I've tested this on extant species that were found as fossils (so they are bleached out), and the patterns were correct on some of them, and on other specimens, the patterns that should be there did not show up, so it doesn't always work. It seems that pigmented areas can have a difference in texture of the shell, but it is not a necessity.

[LoneRanger]

Yesterday I collected at a late Mississippian subperiod site in West Virginia and came across a small brachiopod in grey limestone matrix that has pink coloration.  Using magnification, I can see that this color is only present in an extremely thin surface layer.  I would like to think that the original shell color is preserved, but there are alternative explanations for the color.  In any case, it's an interesting piece.

[cngodles]

Here is a paper on color patterns of Pennsylvanian (Late Carboniferous) Gastropoda.

 

Hoare, R.D., Sturgeon, M.T., 1978, Color Patterns on Pennsylvanian Gastropods from Ohio, Ohio Journal of Science Vol 78, 10 p.

 

[SteveE]

The idea of paleo color inspires me to mention the (controversial) idea that the cambrian explosion may have been at least partly driven by the evolution of eyesight.   Interesting read...

In the Blink of an Eye: How Vision Kick-Started the Big Bang of Evolution.
Andrew Parker, 2017
ISBN 9780565094003

 

 

[JamieLynn]

Just found this topic and am very interested because I have a few items from the Cretaceous that I think may have some coloration on them.  As the OP says, there are some Texas Cretaceous oysters that have color patterns still visible. This is Exogyra tigrena. The zig zag pattern just amazes me. 

 

And I have come a cross a few echinoids that seem to have stripes and spots. Now, these may be mineralization coloring but they are awfully regular to be just mineralization.....

 

Loriolia rosana - under the microscope camera which shows the stripes a little better than in natural light (second photo)

 

 

A Leptosalenia texana .  Now this one may be mineral staining because those are kind of "hollows" where the coloration is. 

[Lone Hunter]

A little late to the party with some Cretateous fossils,  gastropods, clams, Ostrea or Cassotrea ? (both valves) and Texigryphea that I find in various colors. I'm assuming anything not the color of concrete is original shell color, what determines whether shells are preserved this way and others are not?

[Quriosity]

A late comment as well, but residual colors in Eocene shells from the Paris Basin have been studied extensively. Colors tend to fade very quickly but pigments remain which can be unveiled chemically and under UV light. Some examples can be seen in this chapter (in French unfortunately but deep.com will help!): https://www.researchgate.net/publication/259762640_Les_motifs_colores_residuels_des_coquilles_lutetiennes_du_bassin_de_Paris