Preservation of colour in fossil shells

[Missourian]

14 hours ago, Lone Hunter said:

I was thrilled to find a big slab of colorful bivalves, a far cry from the cement colored fossils I usually find.        North Texas, Cretaceous Eagle Ford

 

Nice colors. Those remind me of the blue banding I found on a shell in the swash in Florida:

 

 

Unfortunately, and ironically, this soon faded to a dull white as it dried.

[grandpa]

Just a smidge over a year late getting to this party, but I can't help but ask:

 

What do you suppose the evolutionary advantage is for snails to have such integrate, geometric patterns as some of those below that look like some artist painted them?  For whose eyes are these aesthetic, complicated geometric patterns intended and to what purpose?

[Fossildude19]

2 minutes ago, grandpa said:

Just a smidge over a year late getting to this party, but I can't help but ask:

 

What do you suppose the evolutionary advantage is for snails to have such integrate, geometric patterns as some of those below that look like some artist painted them?  For whose eyes are these aesthetic, complicated geometric patterns intended and to what purpose?

 

 

My guess would be some sort of camouflage to break up the outline of the shell against the sea floor.

[grandpa]

1 minute ago, Fossildude19 said:

 

My guess would be some sort of camouflage to break up the outline of the shell against the sea floor.

But such intricate, ornamental, mathematical design?  What a marvel and a thrill to see! 

[pachy-pleuro-whatnot-odon]

3 minutes ago, grandpa said:

But such intricate, ornamental, mathematical design?  What a marvel and a thrill to see! 

 

I seem to remember from one of the articles posted above that while a shell's actual colour isn't always preserved, the light and dark patterns that sometimes are, were present to introduce patterns of shading - that is, lightening and darkening - into the shell. Which would support Tim's supposition that that may

 

9 minutes ago, Fossildude19 said:

be some sort of camouflage to break up the outline of the shell against the sea floor.

 

And when one considers this, the uniform patterning probably reflects a similar uniformity in light breaking through the waves at the water depth these snails used to live at.

[Fossildude19]

Nature is pretty marvelous.   

[Tidgy's Dad]

8 minutes ago, grandpa said:

But such intricate, ornamental, mathematical design?  What a marvel and a thrill to see! 

Indeed it is. They are beautiful

But not a design as in designed.

These shells are all a little bit different and throughout many generations some may have patterns that are better suited to the function, perhaps camouflage, and will have a greater chance of survival and of passing on their genetic material than certain other patterns. So some patterns will perhaps become dominant over others.

[FranzBernhard]

12 hours ago, Tidgy's Dad said:

So some patterns will perhaps become dominant over others.

Ha!

 

Compare these from the "Florianer Schichten" (Langhian):

On 5/20/2021 at 4:55 PM, FranzBernhard said:

Here are some more from the same site as above (Fuggaberg-3), untreated.

And a batch from site Höllerkogel-21, field of view is about 4 cm:

 

 

With that, about 3 Million years younger, from the Feldbach-Formation (Seravallian):

On 5/28/2021 at 6:48 AM, FranzBernhard said:

Some individuals, field of view is 38 mm. These snails are about 3 Million years younger than the one from the "Florianer Schichten". They don´t show that much variation in pattern, they are all sticking to the same style :

 

 

Pick the most similar from the two older batches, five points . I see at least three, perhaps more.

 

Franz Bernhard

Edited December 19, 2023 by FranzBernhard

[grandpa]

@FranzBernhard I was hoping you'd chime in.  Fascinating fossils. 

[Coco]

I love these naticidae (I think it is this family).

 

Coco

[FranzBernhard]

2 hours ago, Coco said:

I love these naticidae (I think it is this family).

These belong to the neritidae. They feed on algae or detritus.

Genus Theodoxus / Agapilia / Vitta / Nerita.

Theodoxus - Wikipedia

Freshwater or brackish water.

Franz Bernhard

Edited December 19, 2023 by FranzBernhard

[Tidgy's Dad]

7 hours ago, FranzBernhard said:

Ha!

 

Compare these from the "Florianer Schichten" (Langhian):

 

With that, about 3 Million years younger, from the Feldbach-Formation (Seravallian):

 

Pick the most similar from the two older batches, five points . I see at least three, perhaps more.

 

Franz Bernhard

Quite.

But I did say "may" and "perhaps".

Maybe sometimes a random pattern is not an evolutionary advantage or disadvantage so could be retained.

Or possibly the variations are an advantage?

And there could be variations that we don't see that were disadvantageous and died out.

[pachy-pleuro-whatnot-odon]

1 hour ago, Tidgy's Dad said:

Quite.

But I did say "may" and "perhaps".

Maybe sometimes a random pattern is not an evolutionary advantage or disadvantage so could be retained.

Or possibly the variations are an advantage?

And there could be variations that we don't see that were disadvantageous and died out.

 

Exactly. Leaving aside the possibility of sexual selection amongst snails, traditional evolutionary theory tells us that mutations occur randomly over time. Most of these will end up being spandrels, that is changes that affect the individual neither negatively nor positively. However, given a certain population size, these mutations will stack over time, eventually leading to more significant variations that may either benefit or negatively influence the survival chances of an individual. When that happens, those that are negatively affected will be removed from the gene-pool, whereas those that benefit from their ancestors' mutations will have a greater chance to procreate and pass on these genes.