Trillobite (?) fossil from father, not sure what it is

[Roseman124]

I recently found a fossil that my father got in the 1970’s in Missouri, but not sure if he got it from someone or found it there. It is about 12x8 inches and maybe 6-10 pounds. I know nothing about fossils but got curious and starting doing some research. Looks kind of like a trillobite genus? Appreciate any insight here.

[Thomas.Dodson]

Looks like Isotelus sp. but other members know more about trilobites.

[connorp]

Nice specimen. There are Ordovician trilobites found in Missouri, although from my (albeit limited) experience, it does not look consistent with the matrix of the trilobite-bearing formations. Maybe @piranha will have some thoughts.

[Harry Pristis]

For comparison:

 

 

I am uncertain about the trivial name -- there was some concern that the species was never formally named.

[piranha]

Isotelus "mafritzae" (named for Canadian paleontologist Madeleine Fritz) was in process in the 90's by Rudkin & Tripp, but unfortunately is still awaiting formal description.

 

The large size and grey matrix suggest New York or Ontario: Isotelus gigas

 

Rudkin, D.M., Tripp, R.P. 1989
The Type Species of the Ordovician Trilobite Genus Isotelus: I. gigas Dekay, 1824. Royal Ontario Museum, Life Sciences Contributions, 152:1-19  PDF LINK

[Roseman124]

Have seen others where the fossil is contrasted from the rock around it. Not the case in mine, is that natural or done by someone usually?

[ParkerPaleo]

I've collected Isotelus in eastern Missouri so I know it's possible.  Not sure I recall well enough to judge based on matrix color/quality.  I do think the matrix I collected was much lighter in hue.  Who knows what that quarry looked like in the 70s

[Sjfriend]

On 8/16/2021 at 11:03 AM, Roseman124 said:

Have seen others where the fossil is contrasted from the rock around it. Not the case in mine, is that natural or done by someone usually?

They can be found both ways naturally, fossil standing out or almost impossible to differentiate from matrix. And yes, sometimes people will enhance the fossils to make them stand out better.