Did Ammonites Have Ink Sacks?

[Koss1959]

Just wondering if ammonites had ink sacks like modern squids and other cephalopods?

[Auspex]

Yes, they did! A number of incredible fossils with evidence of the sac and/or duct preserved have been studied, to that conclusion.

[painshill]

yep, as Auspex says, the fossil evidence is there. Here's one such example (heteromorph):

https://www.academia.edu/3721227/SOFT-PART_PRESERVATION_IN_HETEROMORPH_AMMONITES_FROM_THE_CENOMANIAN-TURONIAN_BOUNDARY_EVENT_OAE_2_IN_NORTH-WEST_GERMANY

[Koss1959]

OK thanks!

I have a promicroceras which I found in Lyme Regis. It has a bite mark on it. Around this bite mark is a black "stain". I thought it could be ink. But (assuming) ink would only be preserved if the ink sack was still intact, otherwise the ink would simply wash away in the sea. So I don't think the black mark is ink.

Next I thought about a mineral growth. Not too clued up on this but it seems it could be likely.

Next, this didn't even cross my mind as it seems so ridiculous. But I was looking through the link painshill posted and the soft body preservation looks remarkably similar to what I have on my ammonite. Mine seems to be shaped more randomly and through a loupe, I could not see any structure or pattern. However, I have a pretty untrained eye.

I expect it's most likely a mineral growth of sorts. Here's some pictures.

What do you think?

[painshill]

Unfortunately I don’t think there’s any way to say whether it’s ink or not unless it were associated with a distinguishable sac or duct… or some pretty high-tech analysis was performed on the residue. The balance of probability is that it’s some kind of unrelated mineralisation.

I had some discussion with Darren a while ago about survival of organic pigments, which in this case would be melanins. There’s no reason why an isolated “cloud” or “squirt” of such pigment could not survive (in a form that enabled its degradation markers to be detected). It’s the molecular structure of chemical substances that determines the extent to which they are “degradation-resistant” during the fossilisation process. Organic substances usually have poor degradation-resistance and are decomposed by enzymatic attack from microbial action before they have had a chance to become mineralised. Those which do survive are subject to diagenetic alteration. The organic constituents polymerize into long chains of hydrocarbons that are then resistant to further degradation.

Organic compounds which (in life, in their original state) had a polymerized and highly cross-linked structure to begin with exhibit the best degradation-resistance. Melanins fall into exactly that category. They’re believed to be highly cross-linked heteropolymers bound covalently to “matrix scaffolding” melanoproteins in a granular form and it’s that structure which makes them degradation-resistant – although not completely immune. Melanins also have the ability to bind to certain metallic ions so, even when they have degraded, it is often possible to infer their presence in fossil structures such as melanoctyes from the presence of those residual trace metals (notably copper).

You might also be interested in the linked paper below: “Direct chemical evidence for eumelanin pigment from the Jurassic period” [from a coelid cephalopod] which should give you some idea of the complexity involved in confirming the presence of such pigments:

http://www.pnas.org/content/early/2012/05/18/1118448109.full.pdf+html

[Note that although the article says that there are two types of melanin that’s not completely correct. There are three – neuromelanin being the third - but that’s only found in the brain of primates (especially humans) and is absent in lower species. Although it also has pigmentation properties, its presence in the primate brain is more likely related to its metal-binding abilities.]

[RJB]

Very interesting!