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diabeticwolf

So I finally have an answer to the identity of this fossil I found in a rock quarry in Crescent, Iowa back in 2015... it has been identified as the back half of a eurypterid with the telson attached and nacre. This is a very unusual find for the location and the age of the shale. 

 

 

 

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Al Dente

I think a flattened nautiloid is a more likely identification. Nacre is calcium carbonate, eurypterids have a chitinous exoskeleton.

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diabeticwolf
6 minutes ago, Al Dente said:

I think a flattened nautiloid is a more likely identification. Nacre is calcium carbonate, eurypterids have a chitinous exoskeleton.

It was identified by paleontologist Bill Rushlau. He strongly feels that's the correct identification, and that it's not a shell.

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DPS Ammonite

I was not able to find any evidence that any animals created nacre outside of the mollusks. Ask Bill Rushlau for evidence/ a reference paper that suggests that eurypterids had shells of nacre.

 

I suppose that there is a very slight possibility that the shell could have been replaced with precious opal. HCl should dissolve nacre (aragonite) but leave opal untouched. Let us know what the test reveals.

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diabeticwolf
2 minutes ago, DPS Ammonite said:

I was not able to find any evidence that any animals created nacre outside of the mollusks. Ask Bill Rushlau for evidence/ a reference paper that suggests that eurypterids had shells of nacre.

It's the shape and segmentation that makes him believe that this is the back end of a eurypterid with the telson attached. The way it tapers is what caught his attention. When asked about the nacre, he just said it's very unusual. He's in a different state than I am, so he was looking at the same photos. He hopes to travel to meet with me to see it in person. I may take it to a museum to get more input.

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WhodamanHD

Whatever it is, it’s beautiful! Is it possible that instead of Nacre it’s a replacement mineral that has the same optical properties?

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diabeticwolf
2 minutes ago, WhodamanHD said:

Whatever it is, it’s beautiful! Is it possible that instead of Nacre it’s a replacement mineral that has the same optical properties?

I wouldn't know how to tell or test the material.

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DPS Ammonite
7 minutes ago, WhodamanHD said:

Whatever it is, it’s beautiful! Is it possible that instead of Nacre it’s a replacement mineral that has the same optical properties?

Another possibility is that it could be iridescent pyrite/hematite. A good mineralogist or lapidarian in person could determine what the shiny stuff is.

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diabeticwolf
6 minutes ago, WhodamanHD said:

Whatever it is, it’s beautiful! Is it possible that instead of Nacre it’s a replacement mineral that has the same optical properties?

 

2 minutes ago, DPS Ammonite said:

Another possibility is that it could be iridescent pyrite/hematite.

It is very thin and see through. A small amount flaked off while showing it to someone local.

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DPS Ammonite
3 minutes ago, diabeticwolf said:

 

It is very thin and see through. A small amount flaked off while showing it to someone local.

See if it dissolves in acid. Strong vinegar might work. @diabeticwolf Nacre and opal are translucent; pyrite and hematite are not.

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diabeticwolf
Just now, DPS Ammonite said:

See if it dissolves in acid. Nacre and opal are translucent; pyrite and hematite are not.

I don't have access to acid.

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WhodamanHD
1 minute ago, diabeticwolf said:

 

It is very thin and see through. A small amount flaked off while showing it to someone local.

Try putting that in vinegar. Tells you if it’s calcite or not. If it bubbles it’s Calcium Carbonate, if it’s calcium carbonate the likelihood is that it’s not a Eurypterid, but a distorted nautiloid. Unless, perhaps the calcite replaces it in just the same way nacre would be built but I’m not sure that’s possible. I’m thinking this could be opalized

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WhodamanHD
1 minute ago, diabeticwolf said:

I don't have access to acid.

Vinegar= Dilute acetic acid

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diabeticwolf
10 minutes ago, WhodamanHD said:

Vinegar= Dilute acetic acid

It didn't react to the vinegar.

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WhodamanHD
6 minutes ago, diabeticwolf said:

It didn't react to the vinegar.

That means it isn’t calcium carbonate. @ynot knows minerals better than me, does this look opal-like and how might one tell if it was?

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ynot

I have not heard of opal being "flaky", nor of a chitinous  exoskeleton being "opalized".

It appears that whatever the iridescent material is it is on both sides of the fossil.

Does the fossil have any depth into the rock or is it a flat print? look where it crosses the broken edge of the rock. (Check both pieces.)

 

I would refrain from putting anything acid on it as it may destroy the piece.

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diabeticwolf
21 minutes ago, ynot said:

I have not heard of opal being "flaky", nor of a chitinous  exoskeleton being "opalized".

It appears that whatever the iridescent material is it is on both sides of the fossil.

Does the fossil have any depth into the rock or is it a flat print? look where it crosses the broken edge of the rock. (Check both pieces.)

 

I would refrain from putting anything acid on it as it may destroy the piece.

It appears to be flat. 

 

I only put a small flake into vinegar to test. I would not risk damaging the whole fossil. 

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ynot
11 minutes ago, diabeticwolf said:

It appears to be flat. 

That would support the eurypterid ID.

There are a few minerals that can be iridescent.

The best way to be sure what mineral is causing the color would be to have a gas chromatograph done on  it.

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diabeticwolf
12 minutes ago, ynot said:

That would support the eurypterid ID.

There are a few minerals that can be iridescent.

The best way to be sure what mineral is causing the color would be to have a gas chromatograph done on  it.

I don't have a way to do a test like that. 

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ynot
3 minutes ago, diabeticwolf said:

I don't have a way to do a test like that. 

Not many people do.

 

You can send a sample to these guys and they will test it for You...

http://kaygeedeeminerals.com/sem-eds_service

They are reasonable with their price.

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piranha

text and figures from:

 

Schram, F.R. 1984

Upper Pennsylvanian arthropods from black shales of Iowa and Nebraska.

Journal of Paleontology, 58(1):197-209

 

Eurypterida:

Mycterops whitei

 

Diagnosis. -Anterior of prosoma apparently blunt; first mesosomal segment large and subrectangular only slightly wider at midlength than at either end; tail styliform.  Holotype. -PE 25421; Hushpuckney Shale, Swope Fm., Missourian, Upper Pennsylvanian; 3.5 kilometers west of Crescent, Iowa.  Etymology. -In honor of Warren Draper (Ted) White of Omaha, Nebraska.  Description.-PE 25421 is an incomplete and disarticulated eurypterid.  The sculpturing on the cuticle is papillose or spinelike, and thus akin to that noted in other mycteropids.  One component of the holotype (that on the right in Figure 7C) appears to be a substantial portion of a prosoma and part of an attached segment.  The adjacent component on the left is composed of most of a long segment and the three subsequent shorter segments; the anterior margin of this large segment is straight, though somewhat bowed, and thus appears to be a first mesosomal segment and not a prosoma.  Disarticulated remnants of leg joints are scattered between these two larger fossil components.  Several terminal tail fossils are found at the Papillion (SDSNH 4396, Figure 7D), La Platte (SDSNH 21988), and Ft. Calhoun (SDSNH 4395, Figure 7E) localities.  Though not associated with any anterior portions of the body, the cuticle on these tail specimens is papillose and spinelike, like that of the above prosomal specimen, and thus it seems reasonable to assume these tails belonged to the mycteropid.  The terminal three segments of the postabdomen are long and subequal.  The terminal segment has a median ridge extending almost its entire length.  The telson is styliform, abruptly narrowing from its base, somewhat longer than the terminal postabdominal somite, and marked with a raised area along its dorsal surface.  Remarks. -If the head and tail units are indeed from one species, then these black shale specimens afford the most complete view of what mycteropids were like.  Even the holotype alone is more complete than the known specimens of M. ordinatus Cope, 1886; M. mathieui (Pruvost), 1923; or M. (?) blairi Waterston, 1968.  Still, little light can be thrown on the systematic position of Mycterops.  Kjellesvig-Waering (1959) and Størmer (1974) placed the genus within the eurypteraceans on the admittedly poor evidence of a possible sixth appendage in M. mathieui.  No good information exists for the appendages of M. whitei, but the rather distinctive, very elongate styliform tail might serve to further justify a distinct superfamily for Mycterops in the sense of Størmer (1974).

 

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piranha

Btw, ...iridescent eurypterid... :faint::drool: mail?url=http%3A%2F%2Fmail.yimg.com%2Fok%2Fu%2Fassets%2Fimg%2Femoticons%2Femo57.gif&t=1530234727&ymreqid=2b37d289-e028-403a-1c89-8e000201ba00&sig=vZQosN9ENjiAlwl609UdYw--~C

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Missourian

If there is sufficiently fine preservation, an id positive for a eurypterid would be a pattern of scales on the carapace:

 

post-6808-0-95829400-1325839080.thumb.jpg.8d7903e3eceda601a49797975556ccb6.jpg

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Missourian

In the Pennsylvanian, black shales often have phosphatic preservation, which can preserve very fine details, including perhaps the fine layered structure of nacre.

 

Also, what other types of fossils have been found in the black shale? That can help narrow down an id. It would probably be either deep marine (with conodonts, fish, cephalopods and crustaceans), or shallow water (with plants and perhaps some fresh- and brackish-water arthropods).

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