Trilobites

[Newbie_1971]

I stopped off at a place near my work and .......?

[Kane]

Didn’t provide location information again?

[Ludwigia]

Ya never learn, do ya?

[Newbie_1971]

5 hours ago, Ludwigia said:

Ya never learn, do ya?

NO ... I  guess I  don't. 

[trilobites_are_awesome]

Flexicalymene retrosa.

Edited August 7 by trilobites_are_awesome

[ynot]

6 minutes ago, Newbie_1971 said:

NO ... I  guess I  don't. 

Ya really need to do that or it is less likely to get an accurate identification.

[Ludwigia]

2 hours ago, trilobites_are_awesome said:

Flexicalymene retrosa.

I'd be curious to hear from you what brings you to this conclusion without knowing its provenance.

[Fossildude19]

@Newbie_1971

 

It is enough to just mention State and County to help us out a bit. 

 

Not everyone always hunts the same spots all the time, so it is helpful to let us know where you are finding these.

[trilobites_are_awesome]

10 minutes ago, Ludwigia said:

I'd be curious to hear from you what brings you to this conclusion without knowing its provenance.

They are the most common trilobite in Indiana and they are perfect fit from the provided Images.

[Ludwigia]

6 minutes ago, trilobites_are_awesome said:

They are the most common trilobite in Indiana and they are perfect fit from the provided Images.

 

I did some googling and found a lot more F.meeki trilobites, for which they could also be construed, in Indiana than F. retrosa, which seem to have an overabundance in Ohio. Are they synonymous? 

[Kane]

9 minutes ago, trilobites_are_awesome said:

They are the most common trilobite in Indiana and they are perfect fit from the provided Images.

There may not be enough clear diagnostic information to make that call. There would likely have to be a very clear image of the glabella overall, glabellar lobes, and genals to make a more determined distinction. 

[trilobites_are_awesome]

You both have good points.

we need better pictures to ID for sure.

[connorp]

Great example of why locality information is so important for IDs. If the formation was known, the species could be readily identified since the distribution of Flexicalymene species in the Cincinnatian is well known. But for whatever reason, OP refuses to include such information despite being asked repeatedly to do so. At this point, whether intentional or not, it comes across as disrespectful to those trying to offer help. So I won't be replying further.

[piranha]

The size, shape and angle of the anterior border are the distinguishing features that differentiates Flexicalymene meeki and Flexicalymene retrorsa. 

 

Brandt 1980 treated them as synonymous and subsequently Brandt & Davis 2007 regards them as separate based on the description of Ross 1967.

 

 

Flexicalymene cf. F. retrorsa (Foerste) has little to distinguish it from F. meeki except the size, shape, and inclination of the anterior cranidial border. Foerste's original criteria included these and, in addition, lesser cranidial width (trans.) at the posterior border and lack of vestiges of genal spines; I have been unable to substantiate either of these. From Flexicalymene senaria this species does differ in its wider cranidium, straight rather than convex lateral outline of the glabella, inclination and shape of the anterior border, depressed axis of pygidium, and short terminal piece of pygidial axis. The species may have limited stratigraphic use.

 

Ross, R.J. 1967

Calymenid and other Ordovician Trilobites from Kentucky and Ohio.

United States Geological Survey Professional Paper, 583B:1-19  PDF LINK

 

 

Foerste’s species of Flexicalymene, Amphilichas, and Autoloxolichas have survived taxonomic scrutiny (other than reassignment to newer genera), but the many species of Flexicalymene are in dire need of modern taxonomic review. Ross (1967) acknowledged F. retrorsa, but with reservation, as it “has little to distinguish it from F. meeki except the size, shape, and inclination of the anterior cranidial border” (Ross, 1967, p. 15), which are character states that he was unable to substantiate. Ross (1967, p. 16) concluded that “the species may have little stratigraphic use.” Flexicalymene retrorsa minuens has not been referred to in recent literature, and is generally regarded as a synonym of F. retrorsa.

 

Brandt, D.S., Davis, R.A. 2007

Trilobites, Cincinnati, and the "Cincinnati School of Paleontology". pp. 29-50

In: Fabulous Fossil: 300 Years of Worldwide Research on Trilobites.

New York State Museum Bulletin, 507:1-248   PDF LINK

 

 

F. meeki and F. retrorsa were originally distinguished by "more obtuse genal angles" and a more strongly "reflexed" border in F. retrorsa (Foerste, 1910). Foerste elaborated on the distinction in 1919; he explained that F. retrorsa was characterized by "rounded genal angles, a narrower, less triangular cephalon, and a shorter, less nasute anterior border." The results of cluster and discriminant analyses suggested Richmondian trilobites were distinct from Maysvillian forms, but these analyses were not based on the morphologic features Foerste used to distinguish F. meeki and F. retrorsa. I could not substantiate this distinction in genal angles, "reflexion" of the anterior border, and outline of the cephalon with quantitative methods because of lack of enough well-preserved specimens. The anterior border is easily deformed, and measurements of G, G1, and G2 were highly variable, a variation I attribute more to preservation than to allometric growth because many of the specimens show "obvious" compression of the anterior border. The width of the cephalon is also sensitive to deformation by compression of the librigenae along the facial sutures, and these measurements were also discarded as unreliable. Qualitatively, recognition of the differences between trilobites assigned to F. meeki and F. retrorsa is very subjective for the trilobites collected in this study alone show a wide range of variation in the inclination of the anterior border and roundness of the genal angles. Because the criteria used to originally distinguish these species can not be substantiated by quantitative techniques, and because intermediate morphologies are common, I chose to synonomize F. retrorsa and F. retrorsa-minuens with F. meeki.

 

Brandt, D.S. 1980

Phenotypic Variation and Paleoecology of Flexicalymene (Arthropoda: Trilobita) in the Cincinnatian Series (Upper Ordovician) near Cincinnati, Ohio.

MSc Thesis, University of Cincinnati, 148 pp.

 

 

 

 

figures reprinted and published in:

 

Scheer, A.W. 2019
Flexicalymene Species Determination.

M.A.P.S. Digest 42(2):51-55  LINK