crustacean fragment

[M Harvey]

This has been bugging me for years.  Found in Montgomery, Al in the lower Selma chalk.  Pretty sure it is a crab claw segment but fascinated by the color and texture.  Does anyone know if original pigmentation can be preserved?  

[Lone Hunter]

Pretty sure it's not crab, kinda looks like part of a shell with something on it, bryozoanish maybe?  Novice guess.

[JohnJ]

Looks like part of a crab to me.

 

@MB

[pachy-pleuro-whatnot-odon]

Yeah, also looks like crab to me. I've got a piece like this (unfortunately inaccessible to me right now) from the Isle of Wight. Extent crabs can have similar roughened textures, so I think there's little doubt about this being crustacean. The patterning may even reveal the species to the expert... Some members I know who are certainly not too crabby about crabs and may be able to identify (if at all possible) are @glu, @caterpillar, @mamlambo and @RJB.

 

As to the preservation of colour: not sure. Colour can, of course, be preserved by way of melanin (sometimes incorrectly referred to as melanosomes) - eumelanin for brown and black and pheomelanin for red - in such integumental structures as hair and feathers, but also in soft tissues such as skin and organs. But whether it could be preserved in the chitin and calcium carbonate shells in crabs, I don't know.

 

A quick search on Google suggests that molluscs do use melanin in their shell structure, which opens the possibility of this surviving the fossilisation process. In fact, I have a Triassic shell in my collection that has black lines running down its length that are probably created by melanin, as the shell has no structural/three-dimensional ornamentation whatsoever. Which begs the question of whether crab shells contain melanin. I was unfortunately not able to quickly find the answer to that question, but did find out the following (source):

 

Quote

A crustacean’s exoskeletons contain several chemicals called pigments, which give the crabs and prawns their colour. One of these is an orange-ey pigment called “astaxanthin”. This is a member of the family of pigments that is responsible for colouring many of the yellow, orange and red animals.

 

When the crustaceans are alive, the astaxanthin is tightly wrapped up and trapped by a special protein called “crustacyanin”. This is why live crabs and prawns usually look bluish-grey.

 

This suggests crabs would turn red when they die as the crustacyanin decays. But as I don't think astaxanthin has been studied or found in fossils yet, I'm not sure whether the brownish colour in your specimen is due to the crabs original colours or is just an artefact of preservation. Interestingly, the piece of crab from the IoW I mentioned before also has a strong brown colour, as do, I believe, some of the specimens found by @mamlambo.

[Plax]

crab bit weathered brown for me.

[caterpillar]

I think it's a bit of crab. But an ID is very difficult

[RJB]

 I would say to ID a crab from this would be difficult, but to me it looks more like the Carpus and not Chela, (not claw)

 

RB

[M Harvey]

5 hours ago, pachy-pleuro-whatnot-odon said:

Yeah, also looks like crab to me. I've got a piece like this (unfortunately inaccessible to me right now) from the Isle of Wight. Extent crabs can have similar roughened textures, so I think there's little doubt about this being crustacean. The patterning may even reveal the species to the expert... Some members I know who are certainly not too crabby about crabs and may be able to identify (if at all possible) are @glu, @caterpillar, @mamlambo and @RJB.

 

As to the preservation of colour: not sure. Colour can, of course, be preserved by way of melanin (sometimes incorrectly referred to as melanosomes) - eumelanin for brown and black and pheomelanin for red - in such integumental structures as hair and feathers, but also in soft tissues such as skin and organs. But whether it could be preserved in the chitin and calcium carbonate shells in crabs, I don't know.

 

A quick search on Google suggests that molluscs do use melanin in their shell structure, which opens the possibility of this surviving the fossilisation process. In fact, I have a Triassic shell in my collection that has black lines running down its length that are probably created by melanin, as the shell has no structural/three-dimensional ornamentation whatsoever. Which begs the question of whether crab shells contain melanin. I was unfortunately not able to quickly find the answer to that question, but did find out the following (source):

 

 

This suggests crabs would turn red when they die as the crustacyanin decays. But as I don't think astaxanthin has been studied or found in fossils yet, I'm not sure whether the brownish colour in your specimen is due to the crabs original colours or is just an artefact of preservation. Interestingly, the piece of crab from the IoW I mentioned before also has a strong brown colour, as do, I believe, some of the specimens found by @mamlambo.

Great answer.  Thanks for  doing the research.

[pachy-pleuro-whatnot-odon]

2 hours ago, M Harvey said:

Great answer.  Thanks for  doing the research.

 

No problem, your question got me intrigued

[MB]

Yes, that's a bit of crab, I don't think with the original colour, but in exceptional cases you can find at least a clue of what could have been the pattern distribution of colour, but I don't think the original colour. 

It is exceptional, but I saw the round dark spots on the carapace of a Harpactoxanthopsis guadrilobatus exactly as they are in Carpilius maculatus.

Maybe some analyisis could be carried out in that issue, but nobody did it.

Edited May 2, 2021 by MB

[M Harvey]

1 hour ago, MB said:

Yes, that's a bit of crab, I don't think with the original colour, but in exceptional cases you can find at least a clue of what could have been the pattern distribution of colour, but I don't think the original colour. 

It is exceptional, but I saw the round dark spots on the carapace of a Harpactoxanthopsis guadrilobatus exactly as they are in Carpilius maculatus.

Maybe some analyisis could be carried out in that issue, but nobody did it.

Here's a pic of the fragment next to a piece of Dungeness crab I found last weekend.  It's so interesting how little the morphology of crabs have changed over the last 85  million yrs.

IMG_2374.CR2

[pachy-pleuro-whatnot-odon]

Converted the above file for easier viewing

 

[M Harvey]

I didn't realize it was still in RAW.  Thanks

[MB]

There was crucial moments at the end of Jurassic, in Mid-Cretaceous and in the Eocene. Since Eocene times, almost all of the decapod forms (Families) that inhabit our waters were presents already.