Help to ID Trilobites fron Wheeler Formation

[gerardo gonzalez]

Hello friends, I need your help to learn a little more, I am not an expert in trilobites, in fact what I own are the Brachiopods, but accommodating my fossils, I found myself very similar and they filled me with doubts, can you could help me distinguish between an interstricted Peronopsis and a Ptychagnostus atavis, both of the Upper Cambrian, of the Wheeler Formation, in House Range, Millard county, Utah. Thank you.

[DevonianDigger]

That would appear to be a nice little Itagnostus interstrictus, formerly Peronopsis interstricta (Öpik, 1979) from the Wheeler. Cute little bug!

[DevonianDigger]

Wait, @gerardo gonzalez, are you looking for the ID on the second one? I think I misunderstood what was being asked. I apologize. Let me get back to you, lol.

[DevonianDigger]

Egh, I can't find an answer that makes anymore sense to me either, @piranha would know, or at least could point to the relevant literature.

[piranha]

figures from:

 

Robison, R.A. 1982

Some Middle Cambrian Agnostoid Trilobites From Western North America.

Journal of Paleontology, 56(1):132-160

[DevonianDigger]

Yup. Those are some differences! Thanks as always @piranha !

[gerardo gonzalez]

Huge thanks to piranha, I think with that I'll take care of a little. regards

[Oxytropidoceras]

A couple of related papers that might help are:

 

Palmer, A.R., 1954. An appraisal of the Great Basin 

Middle Cambrian trilobites described before 1900 

(pp. 53-86). United States Geological Survey 264-D 

US Government Printing Office.

https://pubs.er.usgs.gov/publication/pp264D

https://pubs.usgs.gov/pp/0264d/report.pdf

 

 

Robison, R.A., 1984. Cambrian Agnostida of North 

America and Greenland, Part I, Ptychagnostidae.

University of Kansas Paleontological Contribution

Paper 109, University of Kansas, Lawrence, Kansas.

https://kuscholarworks.ku.edu/bitstream/handle/1808/3668/paleo.paper.109op.pdf

https://kuscholarworks.ku.edu/handle/1808/3668?show=full

 

Yours,

 

Paul H.

[Carl]

Just FYI, there is a debate about whether agnostids are trilobites or not:

 

From Wikipedia:

The systematic position of the order Agnostida within the class Trilobita remains uncertain, and there has been continuing debate whether they are trilobites or a stem group. The challenge to the status has focused on Agnostina partly due to the juveniles of one genus have been found with legs differing dramatically from those of adult trilobites, suggesting they are not members of the lamellipedian clade, of which trilobites are a part. Instead, the limbs of agnostids closely resemble those of stem group crustaceans, although they lack the proximal endite, which defines that group. They are likely the sister taxon to the crustacean stem lineage, and, as such, part of the clade, Crustaceomorpha.

[gerardo gonzalez]

Many thanks to: Oxytropidoceras & Carl. The wikipedia discussion I've read it. regards