Possible Pseudosphaerexochus and unidentified Cheirurid pygidia

[andyrice11]

It's been awhile since I've made a post, I've been super busy in my junior year now and have been working quite a lot on my fossil project that will become my senior thesis!

Anyway, today while examining my sphaerexochus specimens, I came across one which looks very different from the rest. From my research thus far it appears to be a Pseudosphaerexochus of some sort. What do you guys think?

 

PART 1: Pseudosphaerexochus? 

 Dorsal view of specimen

Rotated

 

Side view, Notice the prominent S2 furrow. None of my sphaerexochus specimens have this

Pseudosphaerexochus? specimen (left) vs. one of my larger Sphaerexochus romingeri specimens. 

 

PART 2- Unidentified cheirurid pygidia

 

In the process of counting and recording all the Silurian specimens for this project, I came across two pygidia I could not initially identify. I went to my guide to the fossils of Indiana reference book and found a picture that looks identical to the specimens in question. The book says they are Cheirurus niagarensis pygidia, so of course I was satisfied with this ID since I happen to have about a dozen C. niagarensis cephalons in my collection. However, upon further research, I have found that the pygidia specimens I have collected as well as the one mentioned in my reference book more closely resemble Sphaerexochus pygidia. 

 

 Here are two pics showing both of my specimens.

 

Here is the top specimen from the above pictures with the contrast enhanced

 

 

Here is the picture from my reference book that is identified as a Cheirurus niagarensis pygidium

 

 

And here is just one of many pictures I have found showing Sphaerexochus pygidia that resemble both my specimens and the one from my reference book

 

Both Cheirurus and Sphaerexochus belong to the family Cheiruridae, so it makes sense that they might have very similar looking pygidia. However, I have yet to find any pictures (online or in text) that show a cheirurus pygidium that looks similar to the ones I have found. Perhaps my reference book has an incorrect identification or I just haven't done enough research yet!  

[Fossildude19]

@piranha

[piranha]

Pseudosphaerexochus is restricted to the Ordovician:

 

 

"It is interesting to note that, save for the one clade of trilobites belonging to the genus Sphaerexochus, all of the other species are restricted to the Ordovician."

 

text from:

 

Gapp, I.W., Congreve, C.R., & Lieberman, B.S. (2012)

Unraveling the phylogenetic relationships of the Eccoptochilinae, an enigmatic array of Ordovician cheirurid trilobites.

PloS one, 7(11):e49115   PDF LINK

 

 

Is there one extra furrow or is it a matched pair?  Sphaerexochus does have multiple glabellar furrows, usually not well defined.  The smaller one must be a juvenile.

 

Genus SPHAEREXOCHUS Beyrich, 1845

Diagnosis: "Glabella highly inflated, subcircular in outline, with three pairs of lateral furrows; anterior two pairs relatively weakly impressed, basal pair wide and deep, curving round to meet occipital furrow."

 

text from:

 

Lane, P.D. (1971)
British Cheiruridae (Trilobita). 
Palaeontographical Society London, 530:1-95

[piranha]

Quote

...Perhaps my reference book has an incorrect identification...

 

Yes, that reference is incorrect. 

The figures from the 1959 Treatise shows the additional glabellar furrows and identical pygidium.

 

[andyrice11]

3 hours ago, piranha said:

Pseudosphaerexochus is restricted to the Ordovician:

 

 

"It is interesting to note that, save for the one clade of trilobites belonging to the genus Sphaerexochus, all of the other species are restricted to the Ordovician."

 

text from:

 

Gapp, I.W., Congreve, C.R., & Lieberman, B.S. (2012)

Unraveling the phylogenetic relationships of the Eccoptochilinae, an enigmatic array of Ordovician cheirurid trilobites.

PloS one, 7(11):e49115   PDF LINK

 

 

Is there one extra furrow or is it a matched pair?  Sphaerexochus does have multiple glabellar furrows, usually not well defined.  The smaller one must be a juvenile.

 

Genus SPHAEREXOCHUS Beyrich, 1845

Diagnosis: "Glabella highly inflated, subcircular in outline, with three pairs of lateral furrows; anterior two pairs relatively weakly impressed, basal pair wide and deep, curving round to meet occipital furrow."

 

text from:

 

Lane, P.D. (1971)
British Cheiruridae (Trilobita). 
Palaeontographical Society London, 530:1-95

Thank you! Somehow I skipped over the fact that Pseudosphaerexoxhus is only found in the Ordovician.. There seems to have been a matching furrow on the other side of the specimen but the top layer of sediment is a little worn down so its not very prominent. I have quite a few sphaerexochus cephalons that are about the same size as the unidentified specimen. but they all appear morphologically similar to the larger specimen I have posted here. What strikes me the most about this unidentified specimen is how close together the L1 glabellar lobes are. Also they sort of taper to a point at the top where as the glabellar lobes on all of my other sphaerexochus specimens have a more curved appearance.