A.C. Posted October 19, 2022 Share Posted October 19, 2022 Hey all, Does anyone have any good publications on differences between Flexicalymene meeki and retrosa? Assuming formation is unknown is there any way one could get a relatively positive ID on species? Link to comment Share on other sites More sharing options...
Collector9658 Posted October 19, 2022 Share Posted October 19, 2022 This may be worth reading. https://www.google.com/url?sa=t&source=web&rct=j&url=https://pubs.usgs.gov/pp/0583b/report.pdf&ved=2ahUKEwigqN67z-z6AhXug4kEHfcnAhQQFnoECCsQAQ&usg=AOvVaw2MPLNZMcgaeToeGbjQv9fB 1 Link to comment Share on other sites More sharing options...
piranha Posted October 19, 2022 Share Posted October 19, 2022 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 3 2 Link to comment Share on other sites More sharing options...
erose Posted October 21, 2022 Share Posted October 21, 2022 Often when we we look for different "species" we find the descriptions of differences become vague. you can probably find clear examples of each but if you lay all your specimens out you will in fact find a totally gray scale from one to the next. I found that with some Texas echinoids. I could find ones that obviously matched the descriptions but when all my specimens were laid out there was totally smooth transition from one to the next. Deciding where one stopped and one started ended up being totally arbitrary. I have labeled all my Cinci Flexicalymenes as F. meeki or F. sp. cf. meeki. 1 1 Link to comment Share on other sites More sharing options...
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