Wednesday, March 24, 2010

Waldron Shale Trilobites

Finding trilobites is not an easy thing unless you live in Utah or Morocco near a trilobite quarry. The two trilobite fragments I present in today's post may not seem like much but they are the first pieces of species I have never found before. Both fossils were found in the Waldron Shale of Clark County, Indiana. This layer is also known as the Niagara Group and formed during the Silurian Period.

The first piece made me wonder when it was found, is it part of a trilobite pygidium or some other creature? Not seeing any remnant of three lobes made me doubt it was a trilobite until my friend Herb identified it as a trilobite glabella. After consulting the Fossils of Ohio book's Silurian trilobite section, I found a match as a Cheirurus niagarensis (Hall).  After more research, it was determined it can be found in the Rochester shale of New York and in Indiana,Wisconsin, & Illinois. Note this fossil has not been prepared. 

The image from the book I use for reference purposes below is of a Cheirurus welleri because the picture showed more of the cephalon.  The article states the two species can be confused by the C. welleri has longer glabellar furrows.  It also says this species is found in the Niagaran of Wauwotosa, Wisconsin, Clinton of New York, Waldron of Indiana, Silurian of Tennessee, and Guelph of Ontario.


Image from Plate 4, Figure 7 - photo by George Nelson
New and Old Silurian Trilobites from Southeastern Wisconsin, with
Notes on the Genera of the Illaenidae
by Percy E. Raymond
Bulletin of the Museum of Comparative Zoology at Harvard College
Volume LX No. 1 - January 1916


This next fossil I was unsure of as well because of the cephalon was so rounded (convex) and smooth.  The fossil has an eye exposed. 
Bumastus niagarensis (Whitefield) (Illaenus niagarensis Whitefield) described on page 17 of the article sited under the included images:
The specific characteristics are: -cephalon rather convex, with long dorsal furrows, no lip or concave border on the cephalon. Eyes of medium size, situated nearly their own length from the posterior margin, thorax short, pygidium long, rather pointed behind, with narrow concave border.
I am calling it Bumastus niagarensis (Whitefield) since it was found in the Waldron Shale but its eye area tends to match Bumastus dayi Raymond in my opinion.  Note from article on page 18 about differences:
 It will be once noted that this species is much like B. niagarensis, but has large eyes far back, and the pygidium is shorter and with less depressed margin.
Fossil is unprepared.  Thanks to Herb for help with identification.




Image from Plate 1, Figure 3 - by E.N. Fischer, Del.
New and Old Silurian Trilobites from Southeastern Wisconsin, with
Notes on the Genera of the Illaenidae
by Percy E. Raymond
Bulletin of the Museum of Comparative Zoology at Harvard College
Volume LX No. 1 - January 1916

3 comments:

Shamalama said...

Cool, I've never seen Bumastus before.

Fossil Detective said...

I had not either till I found that fossil.

Matt Ignoffo said...

Regarding the cheirurid at the top. I struggled through an id of a fragment recently. Turned out to be Cheirurus welleri. One diagnostic feature was the direction of the glabellar furrows which point in and up in Pseudocheirurus niagarensis and point in and down on Cheirurus welleri. Your pic seems to have aglabella with furrows pointing in and up similar to Pseudocheirurus niagarensis, or mauve it's weathered too much to see the direction the futrows take. I will send you a pic of the piece I believe to be Cheirurus welleri.