Calymenacae and their pygidia
Here is a new page following a discussion about Calymenids on the Yahoo trilobite club. I'd like to say right now that what I present won't provide a solution to all the systematic problems concerning the calymenids :) I wish I could, but the person who undertakes such a task will have to write a full paper, if not a book :) I am neither skilled nor experienced enough to do this.
That being said, this page will try to present remarks, schemes and so on, on the Calymenids in general (or I should say the suborder Calymenina). This might be considered the result of questions about "Diacalymene ouzregui".
Introduction
To open the page, I first present a "genealogic tree" of calymenid pygidia after W. Hammann, based on his study of pygidial coaptative structures (HAMMANN W. 1983. Calymenacea (Trilobita) aus dem Ordovizium von Spanien : ihre Biostratigraphie, Ökologie und Systematik. Abh. senckenberg. naturforsc. Ges., 542 : pp 1 - 177).
Please note that this table was made in 1983 and is probably subject to change (send me a mail if you know of changes here). Phylogenetically, this table might be mostly useless, but I think it is interesting from a systematic point of view. The following scheme might present useful details to some of us :)
Now, time to see some cephalons and to define some basic shapes :)
Remarks
Robert Sensenstein (Ottawa Paleontological Society) posted this message on the Yahoo trilobite club in response to someone who asked: in what genus was the calymenid species breviceps, Flexicalymene or Gravicalymene? Here is his response:
"The presence of papillae (pimple like nodes) projecting into the axial furrow from the lateral glabellar lobes or buttresses projecting into the axial furrow from the fixigena immediately remove the specimen from the possibility of belonging to the genus Flexicalymene. The genus is recognized as having deep, open, steep- walled axial furrows (Whittington, 1971). The primary identifying feature of Flexicalymene is the outline of the glabellar formed by the axial furrow at the first lateral lobe and extending forward anteriorly to the preglabellar furrow. This has been described (Ross, 1967) as "parabolic to subparabolic" in outline and also (Whittington, 1941) as "subtriangular in outline, with rounded anterior end."
Please refer to the figure above for an illustration of this [edit : I did not saved the picture at that time. Sorry for the inconvenience, but the Trilobite club wasnt' supposed to vanish in the Yahoo's limbo ;) ], contrasting it with another fairly common Ordovician genus, Gravicalymene. The axial furrows form approximately straight lines versus the bell shaped outline formed by Gravicalymene. Your specimen of breviceps should have papillae or buttresses.
Not only that but also the location and height of the palpebral lobes in reference to the glabelar lobes and furrows are also a key for description. The shape and curvature of the glabella can be distorted and become an artefact of preservation making it difficult to use acurately unless the specimens are well preserved (inflated). For North American Calymenids, isn't the Calymene genus only found in the Silurian? Listed as Ordovician Calymenids in "A Chronology of North American Ordovician Trilobite Genera," (R. E. Sloan, 1991), are; Protocalymene, Calymenidius, Thulincola, Flexicalymene, Gravicalymene, Platycalymene, Onnicalymene, Calymenella, and Diacalymene but no 'Calymene' genus. No doubt Calymenid classification is a big mess and in serious need of a revision but how that is done will depend if the classifier is a lumper or a splitter. Just my 2-cents worth."
Al Scheer Sat Jan 31, 2004 10:12 pm in an "Emergency ID request!" for Sam :)
Sam, The primary identifying feature of Flexicalymene is the outline of the glabellar formed by the axial furrow at the first lateral lobe and extending forward anteriorly to the preglabellar furrow. This has been described as "parabolic to subparabolic" in outline (Ross, 1967) and also as "subtriangular in outline, with rounded anterior end"(Whittington, 1941). The axial furrows form approximately straight lines versus the bell shaped outline formed by Gravicalymene. Granulosa technically has a bell shaped axial furrow and therefore is not a Flexicalymene.
OK, I will stop here for now, as it is lunch time, please ask your question on the "club" :) I have more things to come later in the day (or night ;) ).
JB