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Unknown Iowa (Pennsylvanian?) Trilobite


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I usually avoid purchasing fossils with little locality information, but this was too neat a specimen to pass up. The only information the seller had was that this trilobite was supposedly collected near Buffalo, Iowa. It looks like a Carboniferous trilobite to me, and the bedrock around Buffalo is Devonian and Pennsylvanian, hence I'm leaning towards this being a Pennsylvanian trilobite.

I was hoping the knowledgeable trilobite folks here might be able to help me identify this trilobite (@Kane @piranha). I was also hoping to narrow down a possible formation/locality of origin. The only reference I've been able to find on Pennsylvanian fossils collected near Buffalo is an old post here by @fishguy – do you have any information about collecting sites in this area?

@minnbuckeye As you collect all over Iowa, I thought I'd see if you might have any insight.

Thanks in advance for any help.





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The pyrite crystals are very showy!dancing smileyThe median preoccipital lobe identifies this one: Ditomopyge scitula mail?url=http%3A%2F%2Fmail.yimg.com%2Fok%2Fu%2Fassets%2Fimg%2Femoticons%2Femo71.gif&t=1661307412&ymreqid=23281213-8dc1-3cff-1c79-240005016700&sig=_rjALnXTZZmYRrw6aFIbyw--~D

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Nice acquisition! The matrix reminds me more of Iowa's Devonian than Pennsylvanian. But I trust @piranha's ID.

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The median preoccipital lobe and the typical axial nodes on the pygidium are textbook features for Ditomopyge.



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That's a good find! I'd recommend doing so research on pyrite decay prevention since the crystals are right up against the fossils.

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4 hours ago, fishguy said:

I trust @piranha's ID also.  I have collected near Buffalo Iowa and the matrix looks similar.   

Thanks. Any ideas on a possible formation of origin?

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The GSA page lists the Pennsylvanian Caseyville and Tradewater formations from the Raccoon Creek Group in Scott, Co. Iowa.


RACCOON CREEK GROUP (primarily Morrowan; locally includes Atokan-lower Desmoinesian Tradewater Formation in upper part). Recognized only in eastern Iowa in Scott and Muscatine counties; includes in ascending order the "Caseyville" and Tradewater formations. Rests unconformably on older map units in the county and fills paleovalleys and paleokarst developed in underlying Silurian and Devonian carbonate rocks. Primary lithologies are: shale/mudstone, light to dark gray, partly silty to sandy; sandstone, very fine to medium-grained; siltstone, gray. Secondary lithologies are: carbonaceous shale/mudstone, gray to black; phosphatic black shale; limestone, dense, partly fossiliferous, partly sandy; coal (beds locally > 2 ft). Minor lithologies are: sandstone, coarse-grained to granular, partly conglomeratic; mudstone, red to pink; limestone concretions (may be septarian); cone-in-cone limestone; siderite/ironstone concretions and pellets; pyritic. Maximum thicknesses: 195 ft (59 m).



This paper correlates Ditomopyge scitula  from the Tradewater Fm. of western Illinois:


Johnson, R.G. 1962

Interspecific Associations in Pennsylvanian Fossil Assemblages. The Journal of Geology, 70(1):32-55

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