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minnbuckeye

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minnbuckeye

I discovered these two rollers in Fayette County , Iowa in the lower Maquoketa, Ordovician.  This location is well known for Anatophrus borreaus trilobites. Though the next lower formation changes abruptly to almost 100% Isotelus. Did I find one of each? Rollers make IDs tough on me.

 

 2019-05-212.thumb.jpg.5e95ebfd7f8e779d955427e42f8f69ee.jpg 

 

Then as long as you "trilo" experts are looking, can you ID the trilo-bits 1,2 and 3 in the next picture? Thanks for helping!! 

 

 2019-05-211.thumb.jpg.c9b3f11a7b5e8a8d2630785e896e56b2.jpg

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Kermits are so cute. :wub:

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I would say #1 is Isotelus as it has more pronounced axial furrows, but I could be wrong.

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minnbuckeye
31 minutes ago, aek said:

more pronounced axial furrows

That is what made me question the ID. @piranha hopefully can take a peak.

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Isotelus looks good on specimen 1 because it has a narrower axial lobe.

 

Anataphrus Whittington 1954 original description: "proposed for asaphid trilobites in which axial furrows are absent"

However, subsequent authors have described the presence of axial furrows as 'essentially devoid' or 'weakly effaced'

 

Anataphrus with axial furrows:

image.thumb.png.9ed95f83d434199a6538f2c7c5b5c767.png

Whittington, H.B. 1954. Ordovician Trilobites from Silliman's Fossil Mount. pp. 119-141

Ordovician Cephalopod Fauna of Baffin Island. Geological Society of America Memoir, 62:1-234

 

 

image.png.f63ed2feb3add3933ec79f405367d7f7.png

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The hypostome of Calyptaulax also has similar features compared to a cheirurid hypostome.  The posted specimen has shoulders highlighted by the arrows.  Fig. 1 Calyptaulax strasburgensis does not have shoulders although many pterygometopids do have prominent shoulders.  Noting the compatible color and preservation, the hypostome could be Calyptaulax sp.

 

image.png.7606d0ec40a5133998aff67dc4e9128b.png

Jacobs, G.S., Carlucci, J.R. 2019. Ontogeny and shape change of the phacopid trilobite Calyptaulax. Journal of Paleontology, 93(6):1105-1125  PDF LINK

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minnbuckeye

@aek, We were correct!!!!  Thanks so much, @piranha. Your insight into trilobites is always impressive!  

 

 Mike 

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