Trilobite ID

[minnbuckeye]

I have been to Graf, Iowa three times in the last 10 years and am always amazed at this site with the shear number of cephalopods exposed in the rock face.  This fourth trip was made to find some material for a forum member. In doing so, I took the time to look closely at the matrix present at Graf. There were gastropods, brachiopods, bivalves ,graptolites, and even trilobites hidden in the rock. I had never noticed this on my previous trips since the cephalopods are overwhelming. I would love to go back another time soon and NOT look at the cephalopods at all, to see what I could find. I am here today to get Identification of the trilo-bits that I found at Graf. My guess is Thelecalymene mammillata. @piranha 

 

@DevonianDigger, if you still are looking for trilobits, I can send a few of these.

 

 

2018-10-009.cxf

[Raggedy Man]

Your ID looks spot on to me. I love hunting Graf. I took Fossilized6s there for his first time earlier in the year right after the MAPS show. Needless to say, it was picked clean. We found a few blocks of those cephalopods, but you could definitely tell a lot of people had been there. When looking at the rock face, go all the way down to the left. There is a spillway that cuts the beds and yields wonderful plates of the cephalopds and exposes the inner shale layers that has trilobits all throughout it. Remember if you're finding cephalopods in the shale you will not find associated trilobites.

[piranha]

text from:

 

Witzke, B.J., & Glenister, B.F. 1987

Upper Ordovician Maquoketa Formation in the Graf Area, eastern Iowa.

North-Central Section, Geological Society of America, Centennial Field Guide, 3:103-108

 

Unlike other carbonate beds in the sequence, the nautiloid rich intervals at Graf lack abundant diminutive fossils (except ostracodes).  However, the nautiloid beds contain rare additional macrofaunal elements represented by phosphatic molds 5 to 20 mm in diameter.  These include gastropods (Murchisonia, Liospria), bivalves (Nuculites), and brachiopods (Diceromyonia).  Normal-sized cranidia and pygidia of the trilobite, Thelecalymene mammillata, are not uncommon in the nautiloid beds (Whittington, 1971); the phosphatized exoskeletons are finely granulated and preserve original shell ultrastructure (Mutvei, 1981).

 

 

Whittington, H.B. 1971

A new calymenid trilobite from the Maquoketa Shale, Iowa.

In: Dutro, J.T. (ed.) 1971. Paleozoic perspectives: a paleontological tribute to G. Arthur Cooper

Smithsonian Contributions to Paleobiology, 3:129-136   PDF LINK

[minnbuckeye]

@Raggedy Man, These trilo-bits came in a darker layer that DID have cephalopods, just not in the disgusting amounts above and below it. The layer had plenty of tiny gastropods, Murchisonia? Did you ever find a cephalon, or even better, a complete one?

 

 @piranha, thanks so much for the info!!!

 

Mike

[Raggedy Man]

Charlie and I found a cephalon or two. I know my wife found several when I took her there. I've been over 10 times and still haven't found a complete one.

 

I'll try to get to the ones we have this week and end a pic if you'd like.

[Fossildude19]

Neat finds, Mike!

Thanks for showing us.