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Sargon

Bivalve internal mold

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Sargon

Is it possible to closely identify this internal mold of a bivalve? Any suggestions? Again, I do not have any exact info on the geological setting, but it could possibly come from Mesozoic strata.

Thank you in advance!

post-7503-0-52554500-1471966095_thumb.jpg

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BobWill

With no more than the "possible" era to go on generally it would be unlikely to identify beyond "clam". The internal mold shows no growth lines or any ornamentation the external surface might have.

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Harry Pristis

It's a cast, not a mold.

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Sargon

Of course, since there is no actual shell there are no growth lines/ornamentation. But I thought that an overall shape could provide the basis for an educated guess :)

Yeah, it's a cast, my bad (English is not my native language, obviously :) )

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BobWill

You were right about mold. No one ever accepted my challenge to show us a peer review paper where these were called casts when this discussion came up before. Pretty well everything else you hear from Harry Pristis is very accurate and always helpful ;)

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Plax

I'm with Harry and too lazy to look for proof ;)

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Plax

6711_18_26-cast-and-mold-fossils.jpg

A drawing of Glycymeris, a clam from the Miocene of Florida. At left is a shell in perfect preservation, a right a steinkern of a similar shell. A steinkern is a cast of the interior of the shell. (Drawing by Betty Crawford)

from

http://www.prehistoriclife.xyz/fossil-collectors/casts-and-molds.html

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Harry Pristis

You were right about mold. No one ever accepted my challenge to show us a peer review paper where these were called casts when this discussion came up before. Pretty well everything else you hear from Harry Pristis is very accurate and always helpful ;)

Thank you for the endorsement, Bob. I didn't realize there was any remaining challenge to the distinction between "cast" and "mold." I did a google scholar search for "casts, molds, and steinkerns" and came up with 591 hits. A brief review of the first few pages will provide an answer to your challenge.

http://scholar.google.com/scholar?hl=en&q=casts%2C+molds%2C+steinkerns&btnG=&as_sdt=1%2C10&as_sdtp=

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BobWill

Thanks harry and Plax for all your trouble but in the last discussion about this we saw plenty of articles with the terms used both ways just as members on the forum do, but none that were peer reviewed. Someone may have also discussed making copies with latex but the disagreement was about steinkerns. Just please post one a link to an article that's not from an online rag that uses cast for steinkern instead of mold. I can post articles that agree with me too but don't have access to peer papers. I can look on this: https://en.wikipedia.org/wiki/Fossil where you can scroll down to casts and molds for a definition which at least has references.

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BobWill

Well you learn something every day. I never knew about the google tool "scholar". Thanks Harry. Now try your search with "internal mold, steinkern" instead of mold, cast, steinkern.

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Harry Pristis

steinkern
[′shtīn‚kərn]
(geology)

Rock material formed from consolidated mud or sediment that filled a hollow organic structure, such as a fossil shell.

The fossil formed after dissolution of the mold. Also known as endocast; internal cast.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

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BobWill

How does your dictionary define internal mold? Also, how do you account for the discrepancy of the usage in the papers from the search I suggested? If you search google scholar for internal cast the first few are about plaster or silicone copies of fossils or references to internal molds or translations from the German, whereas a search for internal mold gets lots of references to steinkerns with virtually no other meanings implied. It's not surprising that people disagree on this. I fully understand the thought process that gets both answers but by far the majority of reliable references I've seen call them internal molds. My field is electronics so I'm not qualified to say either is right for sure, maybe you took that class but I sure would like to hear from a qualified professional on this just so we aren't spreading confusion and bad science. It's essential that we all know what is meant when we use these terms.

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Sargon

Ok guys, I looked up for the right terminology. E.N.K. Clarksons "Invertebrate Palaeontology and Evolution" (4th edition) on page 5 says:

post-7503-0-02199500-1472014572_thumb.jpg

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Harry Pristis

Ok guys, I looked up for the right terminology. E.N.K. Clarksons "Invertebrate Palaeontology and Evolution" (4th edition) on page 5 says:

That is a system of nomenclature like none I've encountered before, Sargon. It is coherent, but it seems to be an answer in search of a problem. I don't know why "core + internal mold" is better or more efficient than "internal cast" or "steinkern." I doubt that Clarkson's system is widely adopted, at least in the USA. But, it is interesting . . . the lack of uniformity of these descriptors.

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tmaier

How many angels can dance on the head of crinoid? :D

Obviously, the official answer will have to factor in the species of crinoid, and the type of dance being performed (waltz, break dance, etc.).

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BobWill

If an original shell can form a "cast" showing the inner surface then what would you call something formed when the original shell dissolves away and the cavity is filled in with minerals seeping in and solidifying? Would the inner surface of the result be a cast or a mold? This time a copy of the internal surface is formed by the steinkern which is now acting as a mold and forming a cast.

Your way, since anything can be a mold as long as it forms something, the resulting concave surface would also have to be a cast and you're left with no easy way to form a mental image from a description like "internal cast or mold".

My way, and the way I've have seen in text books written and used in the U.S., when you read "internal mold" you picture a convex surface with the details of the inside of the shell. When you read "internal cast" you can picture the concave surface of the inside of the original shell which has been cast from the internal mold.

This use of the terms mold and cast is consistent with the way the terms are used in arts and crafts, where a cast is always a copy of the original and a mold is the thing capable of forming a cast. Without this system there is no use at all for the term "internal mold" since anything formed by something else becomes a cast. Do you have another use for that term? If not why do we keep seeing it?

edit: it may help to remember that in art the verb "cast" is used to describe the process when a mold is formed from a sculpture. You cast a mold. But then the noun "mold" is then used to describe the result since it's use is for casting (verb) a copy of the sculpture which results in a cast (noun) of it.

Edited by BobWill

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Plax

the two references I gave were from geologists. This is probably a semantic argument as it was last time. The shell is certainly the mold for the internal cast. This is something that any non-geologist can grasp because it's logical. Illogical, esoteric use of words baffles me.

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BobWill

Logical to a sculptor. That's where paleontologists borrowed the words. The shell is the original just like a sculptor's clay model. The sculptor makes a mold to cast a bronze copy of the original. In our case the original is the inside of the shell and the internal mold is made by nature. Find a paper (not online mag) by a paleontologist (not a geologist) that calls a steinkern an internal cast. There are probably some out there just as the reference from Sargon says "often miscalled cast" but all of what you get when you scholor/google "internal mold" is consistent with what I've said.

How would you define internal mold? Or do you think it is not a valid term? Once you get the hang of it, the system makes it obvious what is being discussed when you use the terms external mold, external cast, internal mold and internal cast. The first and last are concave and the other two are convex. This makes it all so easy to visualize a fossil from a text without images.

This is a semantic argument but for clarity, so we know what is meant by a reference, it is also important to get right. The original poster had it right then got corrected and then found a reference that supported his original terminology. Just scan through the short beginning parts of these papers and explain why the terms they use must be wrong.

http://scholar.google.com/scholar?hl=en&q=internal+mold%2C+steinkern&btnG=&as_sdt=1%2C44&as_sdtp=

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Plax

Stephenson, 1923, The Cretaceous Formations of North Carolina: Part 1. Invertebrate Fossils of the Upper Cretaceous formations.

and more recently: Allmon and Harris 2008, A new Species of turretellina Gastropod from a Turritelliine-dominated limestone in the paleocene of NC

I didn't selectively search for the terms these are just the pdfs I had access to here

Have never said that either of these is right or wrong. Internal mold just isn't logical to me. Folks call steinkerns "deer hearts" and "turtle heads" and I don't think that they believe they are such things; just a descriptive term. I wouldn't correct someone for calling a Squalicorax a "Crow Shark" either. I don't think that the descriptive term "internal cast" regarding a pelecypod steinkern could be misunderstood to be anything but what it is. I realize that internal mold is commonly used of late and it may be that will become the only accepted usage. I really don't feel strongly enough about this to continue when there is ample evidence that both terms are extensively used in the literature.

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tmaier

I really don't feel strongly enough about this to continue when there is ample evidence that both terms are extensively used in the literature.

Yeah, that was my point about the dancing angels. I think you said it better, without the gratuitous use of humorous imagery.

I see these mistakes WAY back for 100+ years, and it is now tradition, so just go with it.

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BobWill

Sometimes a non-answer is really just the answer you expected.

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abyssunder

I think, your answer is a good answer for the first question of this thread. :)

Edited by abyssunder

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