Why is this ammonite iridescent?

[acrocanthosaurus]

I bought this iridescent ammonite and it came with a description card but it didn't say why it was iridescent. Is it because it still contains traces of the original shell?

[abyssunder]

Simply could be explained as the diffraction of the light rays passing through the aragonite layers.

[piranha]

Here is the latest info on ammonoid iridescence.

excerpts and figure from:

Klug, C., Korn, D., De Baets, K., Kruta, I., & Mapes, R.H. (eds.) 2015
Ammonoid Paleobiology: From Anatomy to Ecology.
Springer Publishing, Topics in Geobiology, 43:1-934

 

Background
In the last decade, hundreds of ammonite specimens with undescribed iridescent color patterns have been discovered. Keupp (2005) was the first to describe and illustrate this occurrence, although Reyment (1957) indicated he had seen such a color pattern but did not adequately document this phenomenon. It must be noted that photography of this phenomenon is difficult because this feature is usually more evident as the specimen is moved in the light, and it may for this reason that Reyment could not adequately document it in his 1956 report.
 

These newly recognized color patterns are preserved as iridescent longitudinal bands parallel to the venter on the external surface (presumably the outer prismatic layer) of the shell. These bands are probably the result of the prismatic shell ultrastructure selectively breaking down light into different wavelengths (i.e., different colors), but this phenomenon needs additional study to confirm this assumption and to test in how far the appearance of the color patterns was altered by diagenesis.
 

Iridescent Color Patterns
 

In the last decade, numerous ammonoid specimens with an iridescent color pattern have been discovered. These new patterns are iridescent longitudinal bands on the external surface (the outer prismatic layer?) of the shell. Ammonoids from sites that preserve these iridescent color patterns (it cannot be ruled out entirely that the iridescent appearance might be secondary) have been collected from the Late Jurassic, Russia and Łuków, Poland; the Early Cretaceous, Madagascar and Normandy, France; the Late Cretaceous from Coon Creek, Tennessee and South Dakota, USA.
 

We are aware that the modern nautilids normally have transverse brown, red-brown and purplish-brown bands in the outer shell layer (see Mapes and Landman 2012 for an exception). And yet, those animals might have lived below the euphotic zone where visibility is extremely limited or totally lacking and detection by other visual animals may be extremely limited. Only at night when natural light is limited do these animals move into shallower water. Thus, modern nautilids have color patterns that are not used in any way that is readily apparent.
 

We are aware that the same could be true of the ammonoids with iridescent color patterns. If these iridescent patterns were utilized as a visual condition, these ammonoids must have lived in the euphotic zone (shallow water) as part of the nektonic food web. If the bright iridescent colors displayed on these shells were used for sexual display or as a danger warning to predators (i.e., a signal that indicates “I am poisonous” or “I taste bad”), then to be most effective, the display must be easily seen. If the marine environment was turbid with sediment and other micro particles, which reduced visibility, the ammonoid visibility was probably enhanced by the brilliant iridescent coloration of the shell, presuming they were already iridescent during their life (the iridescence might also be a diagenetic effect). Alternatively, an iridescent, color-banded shell may have also been to break up the light waves in shallow, light-filled environments to help camouflage the ammonites.
 

To our knowledge, iridescent color patterns are unknown in the modern taxa assigned to the phylum Mollusca (which might also point at a taphonomic problem). Also, other than the ammonoids described herein, we are not aware of any fossil mollusks that had this kind of color pattern. Given that this condition is only known for some Mesozoic ammonoids, it appears that possibly, this unique condition became extinct with the demise of the Ammonoidea at the end of the Cretaceous.
 

 

[Guguita2104]

Nice thread!

[goatinformationist]

It is called nacre

[piranha]

Interesting they had not seen the colourful shell layer of many modern shells. Usually occurs under the outer layer of shell. They should have talked to a malacologist.

I forgot to mention in the citation that Royal Mapes and Neal Larson wrote the chapter "Ammonoid Color Patterns".

As they mentioned above:

"To our knowledge, iridescent color patterns are unknown in the modern taxa assigned to the phylum Mollusca..."

Only the section on ammonoid iridescent color was used as it pertains directly to the Original Poster's question.

Royal Mapes has a number of publications on modern cephalopods, including the American Malacological Bulletin.

He already is a malacologist!

[piranha]

On 6/16/2016 at 9:56 PM, fossisle said:

Well I am not sure how he missed the abalone !!

 

 

The answer is quite obvious. The book I cited is about cephalopods, not gastropods.

Ironically, another chapter (De Baets et al.) does have a cited reference about abalone:

 

Iwata, K. (1980)

Mineralization and architecture of the larval shell of Haliotis discus hannai Ino, (Archaeogastropoda).

Journal of the Faculty of Science, Hokkaido University. Geology and Mineralogy, 19(3):305-320

 

De Baets, K., Landman, N.H., & Tanabe, K. (2015)

Ammonoid embryonic development. pp. 113-205

 

In: Klug, C., Korn, D., De Baets, K., Kruta, I., & Mapes, R.H. (eds.) 2015

Ammonoid Paleobiology: From Anatomy to Ecology.

Springer Publishing, Topics in Geobiology, 43:1-934

 

 

 

[doushantuo]

if anybody needs any biomineralization literature,let me know.

meanwhile:

http://eprints.lib.hokudai.ac.jp/dspace/bitstream/2115/36051/1/17(1)_173-230.pdf

http://eprints.lib.hokudai.ac.jp/dspace/bitstream/2115/36691/1/19_3_p305-320.pdf

Edited June 17, 2016 by doushantuo

[sdsnl]

IMG1.jpg

Does Canada's ammolite not count?

[Johannes]

Hi,

abbyssunder has given the right answer about the iridescent shell. It is a hint for originally preserved aragonite, not recrystalized by calcite (or: not completely recrystalized). There are some seldom micropseudomorphs from phospate copycats of aragonitic needle ultrastructure showing a kind of iridescence, I know them from the german Solnhofen deposits and from some russian sites (both caused by different taphonomic processes).

The ammonite shown above has no (!) iridescent colour pattern. These look different, you may check the article(s) of Keupp (I guess he has made the best pictures of this phenomena).

Best regards

Johannes

[Johannes]

Does Canada's ammolite not count?

Yes, the sites in Canada and one old lead deposit in Central Europe are the only occurences I know where you can find ammonite shell preservation of "ammolite-type".

But both occurences have no ammonites showing an iridescent color pattern, as far as I know.

Edited June 17, 2016 by Johannes

[RJB]

Very interesting thread!

RB

[doushantuo]

http://www.ruf.rice.edu/~rau/phys600/p1353.pdf

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.539.3288&rep=rep1&type=pdf

might be relevant,these two documents

Edited June 17, 2016 by doushantuo

[Johannes]

The aragonite is laid down before the the calcitic outer shell and is only exposed by erosion or abrasion of the outer shell.

@ fossisle: Ammonites did not have a calcitic outer shell*. You may should talk to a malacologist.

As you may know, the aragonite shell of ammonites was originally only covered by a thin layer of chonchioline ("false color patterns"). This might be visible in some sprectra of light. If I remember right, there are some patterns in modern molluscs only visible under UV or IR.

*some carboniferous ammonoidea might have some calcite in their organic layers (2-4%), but this is questionable.

Edited June 17, 2016 by Johannes

[fossisle]

@ fossisle: Ammonites did not have a calcitic outer shell*. You may should talk to a malacologist.

As you may know, the aragonite shell of ammonites was originally only covered by a thin layer of chonchioline ("false color patterns"). This might be visible in some sprectra of light. If I remember right, there are some patterns in modern molluscs only visible under UV or IR.

*some carboniferous ammonoidea might have some calcite in their organic layers (2-4%), but this is questionable.

Thanks Johannes, I suppose I am generalizing as well. I was using the wrong term for ammonite outer shell.

Edited June 17, 2016 by fossisle

[Johannes]

Thanks Johannes, I suppose I am generalizing as well. I was using the wrong term for ammonite outer shell.

Hello fossisle,

I think you are mixing things up.

First: color pattern in an ecological meaning are not that kind of chaotic and non-specific iridescence seen on Abalone. So, authors are right with their statement. You should take a look in the articles where the patterns are figured, described and interpreted. You may see the difference.

Second: pointing somebody (who is not able to defend, because he does not reading this (but I will be happy to send your point with a screenshot to Christian)) to ask a malacologist if he is maybe not experienced enough sounds hard, if the discussion is about ammonites and the person which mentioned this did not know that ammonites did not have had a calcitic shell in general. By the way, you did not mention the name of the organic outer layer, which is called periostracum and is preserved sometimes in ammonites. So: you are not wrong with this term.

Third: I would emphasize friendly to read (beside the article of Klug et al 2015) Klug et al 2007: AMMONOID SHELL STRUCTURES OF PRIMARY ORGANIC COMPOSITION.

Sorry for my style of argumenting in this way, but it feels a little bit unfair to accuse somebody (who is not able to defend) that he is working not correct or has no idea of his topic, especially if you havn't read the whole article (and the most important cited sources). I know it is a very academic attitude to be specific... Maybe overdrawn.

No offense meant!

Best regards

Johannes

Edited June 17, 2016 by Johannes

[fossisle]

Hello fossisle,

I think you are mixing things up.

First: color pattern in an ecological meaning are not that kind of chaotic and non-specific iridescence seen on Abalone. So, authors are right with their statement. You should take a look in the articles where the patterns are figured, described and interpreted. You may see the difference.

Second: pointing somebody (who is not able to defend, because he does not reading this (but I will be happy to send your point with a screenshot to Christian)) to ask a malacologist if he is maybe not experienced enough sounds hard, if the discussion is about ammonites and the person which mentioned this did not know that ammonites did not have had a calcitic shell in general. By the way, you did not mention the name of the organic outer layer, which is called periostracum and is preserved sometimes in ammonites. So: you are not wrong with this term.

Third: I would emphasize friendly to read (beside the article of Klug et al 2015) Klug et al 2007: AMMONOID SHELL STRUCTURES OF PRIMARY ORGANIC COMPOSITION.

Sorry for my style of argumenting in this way, but it feels a little bit unfair to accuse somebody (who is not able to defend) that he is working not correct or has no idea of his topic, especially if you havn't read the whole article (and the most important cited sources). I know it is a very academic attitude to be specific... Maybe overdrawn.

No offense meant!

Best regards

Johannes

No offence taken and perhaps my comment was offensive which I applogize for. It is a very complex subject, but mollusc is a general term referring to a wide array of genera, so my problem is in not recognizing iridescence aragonite is present in modern and fossil molluscs. I am obviously not an expert but have observed not only nacre but very colourful "ammolite"like shell in modern and fossil shells

[fossisle]

I have withdrawn my comments, it is not my intention to offend the authors.

[Johannes]

so my problem is in not recognizing iridescence aragonite is present in modern and fossil molluscs. I am obviously not an expert but have observed not only nacre but very colourful "ammolite"like shell in modern and fossil shells

"Iridescent aragonite" is not identical with "iridescent color patterns". Of course a lot of recent molluscs have iridescent aragonite, but not such color patterns.

[Wrangellian]

Maybe I missed something, but it's not clear to me how this discussion about a specific type of iridescence came about from the original post, nor how that ammonite's iridescence differs from that of the Somerset or Hornby Island ammonites.. to my eye they are about the same (like mother of pearl/nacre). Anyone got a short answer for me?

Edited June 18, 2016 by Wrangellian

[Johannes]

Maybe I missed something, but it's not clear to me (1) how this discussion about a specific type of iridescence came about from the original post, nor (2) how that ammonite's iridescence differs from that of the Somerset or Hornby Island ammonites.. to my eye they are about the same (like mother of pearl/nacre). Anyone got a short answer for me?

I try to keep it short (see numbers in quoting).

1) offtopic, posts on patterns (starting with post n° 3) have nothing to do with the initial question. But contain some maybe informative issues.

2) it differs not (in general). Is the usually optical effect of mother of pearl / reflection on distinct layers of a transparent material. There are some slight differences in preservation of shells structure, depending on the different species/diagenetic issues of the different sites.

Edited June 18, 2016 by Johannes

[piranha]

On 6/18/2016 at 1:38 AM, Johannes said:

1) offtopic, posts on patterns (starting with post n° 3) have nothing to do with the initial question. But contain some maybe informative issues...

 

 

Actually, post number 3 is very germane to the topic.

Here is the first part of the Original Poster's question:

 

"I bought this iridescent ammonite and it came with a description card but it didn't say why it was iridescent."

 

Again, here are the salient points on ammonoid iridescence from post number 3:

 

We are aware that the same could be true of the ammonoids with iridescent color patterns. If these iridescent patterns were utilized as a visual condition, these ammonoids must have lived in the euphotic zone (shallow water) as part of the nektonic food web. If the bright iridescent colors displayed on these shells were used for sexual display or as a danger warning to predators (i.e., a signal that indicates “I am poisonous” or “I taste bad”), then to be most effective, the display must be easily seen. If the marine environment was turbid with sediment and other micro particles, which reduced visibility, the ammonoid visibility was probably enhanced by the brilliant iridescent coloration of the shell, presuming they were already iridescent during their life (the iridescence might also be a diagenetic effect). Alternatively, an iridescent, color-banded shell may have also been to break up the light waves in shallow, light-filled environments to help camouflage the ammonites.

 

BTW, ten people marked post number 3 as informative.

 

 

 

[JohnBrewer]

All the psiloceratids I've seen from Somerset, UK are flattened and are iridescent. They are quite beautiful and stand out in my collection

Not one of mine but most are similar

[Wrangellian]

Actually, post number 3 is very germane to the topic.

Here is the first part of the Original Poster's question:

"I bought this iridescent ammonite and it came with a description card but it didn't say why it was iridescent."

Again, here are the salient points on ammonoid iridescence from post number 3:

We are aware that the same could be true of the ammonoids with iridescent color patterns. If these iridescent patterns were utilized as a visual condition, these ammonoids must have lived in the euphotic zone (shallow water) as part of the nektonic food web. If the bright iridescent colors displayed on these shells were used for sexual display or as a danger warning to predators (i.e., a signal that indicates “I am poisonous” or “I taste bad”), then to be most effective, the display must be easily seen. If the marine environment was turbid with sediment and other micro particles, which reduced visibility, the ammonoid visibility was probably enhanced by the brilliant iridescent coloration of the shell, presuming they were already iridescent during their life (the iridescence might also be a diagenetic effect). Alternatively, an iridescent, color-banded shell may have also been to break up the light waves in shallow, light-filled environments to help camouflage the ammonites.

BTW, ten people marked post number 3 as informative.

I appreciate this info but it seemed like they were talking only about a specific type of iridescence, and the map showing the locations where these ammos are found excluded Somerset and Hornby Island, and maybe other places with iridescent ammos as well, and the accompanying text seemed to preclude any others. What's the difference? Something about actual patterns in the iridescence as opposed to simple MOP? I have never heard of this or seen any pics so I don't know.

[piranha]

On 6/18/2016 at 5:52 PM, Wrangellian said:

...What's the difference? Something about actual patterns in the iridescence as opposed to simple MOP? I have never heard of this or seen any pics so I don't know.

 

 

Correct, the localities on the map are examples of iridescent color patterns.

 

 

figures from:

 

Mapes, R.H., & Larson, N.L. (2015)

Ammonoid Color Patterns. pp. 25-44

In: Klug, C., Korn, D., De Baets, K., Kruta, I., & Mapes, R.H. (eds.) 2015

Ammonoid Paleobiology: From Anatomy to Ecology.

Springer Publishing, Topics in Geobiology, 43:1-934