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minnbuckeye

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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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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

 

 

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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.

 

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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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