rocou3rd Posted December 5, 2014 Share Posted December 5, 2014 Hello. This is a trilobite of weeks formation Utah. When I bought it , it was named Coosella sp. by dealer. Coosella has more big pygidium and the shape of pygidium is like Heart, and the pygidium and the pleural lobe of This specimen is like Modocia weekensis. However I think that M. weekensis has small check spine and this specimen doesn't have . I want to know information about this specimen. Link to comment Share on other sites More sharing options...
Fossildude19 Posted December 5, 2014 Share Posted December 5, 2014 Can't help with ID, other than to say I think it looks more like Modocia weeksensi than Coosella. I have enlarged and brightened your pictures a bit for other opinions. Regards, Tim - VETERAN SHALE SPLITTER VFOTM --- APRIL - 2015 __________________________________________________ "In every walk with nature one receives far more than he seeks." John Muir ~ ~ ~ ~ ><))))( *> About Me Link to comment Share on other sites More sharing options...
Fossildude19 Posted December 5, 2014 Share Posted December 5, 2014 Compare to these Modocia Coosella Tim - VETERAN SHALE SPLITTER VFOTM --- APRIL - 2015 __________________________________________________ "In every walk with nature one receives far more than he seeks." John Muir ~ ~ ~ ~ ><))))( *> About Me Link to comment Share on other sites More sharing options...
FossilDAWG Posted December 5, 2014 Share Posted December 5, 2014 Here you go: Coosella seems reasonable to me. Hopefully Scott will have something to say. Don Link to comment Share on other sites More sharing options...
jgcox Posted December 5, 2014 Share Posted December 5, 2014 Looking at the comparison photos I would agree on Coosella also. Link to comment Share on other sites More sharing options...
rocou3rd Posted December 5, 2014 Author Share Posted December 5, 2014 Thank you for the variable advices! Incidentally, the length of this specimen is 25mm. Link to comment Share on other sites More sharing options...
piranha Posted December 5, 2014 Share Posted December 5, 2014 The eye position next to the glabella, distinctive occipital ring, and pygidium looks like a good match with Modocia whiteleyi: Robison, R.A., & Babcock, L.E. (2011) Systematics, paleobiology, and taphonomy of some exceptionally preserved trilobites from Cambrian Lagerstätten of Utah. University of Kansas, Paleontological Contributions, 5:1-47 OPEN ACCESS PDF 2 Link to comment Share on other sites More sharing options...
piranha Posted December 5, 2014 Share Posted December 5, 2014 I found another example of Modocia whiteleyi that matches well with the free cheeks closely attached. Note again, the proximity of the eyes to glabella, matching occipital ring, thoracic pluerae and pygidium. Link to comment Share on other sites More sharing options...
FossilDAWG Posted December 5, 2014 Share Posted December 5, 2014 Scott, I'm happy to defer to your expertise, but I admit that I'm confused about the facial suture. Every image of Modocia I have looked at shows a distinct angle compared to a gentle curve in Coosella, and the specimen in question has the smoothly curved suture pattern. Is this just some trick of the camera angle? The pygidium looks Modocia-like in some photos and Coosella-like in others, especially the oblique photo where you can get (it seems to me) a better sense of how far the axis extends onto the pygidium, and the notch at the posterior tip of the pygidium. Also the pygidium of Modocia seems to have a ridge around the margin that I don't see in the specimen. I agree the eyes are positioned close to the glabella, as in Modocia. The occipital ring of the two genera seem similar to me, in the two photos Fossildude posted. One thing about trilobite photos that I often find hard to deal with is the differences that can be produced by different lighting, as slightly different angles to the light can accentuate some features and obscure others. I guess that's why the standardized lighting conditions used in scholarly papers are so important. Anyway I find this specimen confusing, with some Modocia-like features and some that seem Coosella-like, especially when seen (by my eye) from certain angles. I'm sure things would be clearer if one could see the actual specimen. Don Link to comment Share on other sites More sharing options...
piranha Posted December 5, 2014 Share Posted December 5, 2014 In the last comparison photo (post #8) the right facial sutures appear to be a close match to my eye. The ridge on the margin of the pygidium also appears to be present, although slightly flattened in the posted example. A lot of variability exists between specimens, so it's always a challenge to get the perfect match. I'd exclude Coosella because it has weak pygidial ribbing that does not extend to the margin. Additionally, the terminal axial piece typically extends only to a mid-point of the pygidium. Attached for comparison are various Coosella morphotypes from the Weeks Formation. Link to comment Share on other sites More sharing options...
FossilDAWG Posted December 5, 2014 Share Posted December 5, 2014 Thanks. I admit I also have some difficulty with the isolated pygidia I collect in the Conasauga Formation. There seems to be a lot of variation in the incurving at the posterior end, and also specimens of other genera sometimes have the margin of the pygydium eroded so as to produce a false curve. Don Link to comment Share on other sites More sharing options...
rocou3rd Posted December 6, 2014 Author Share Posted December 6, 2014 Thanks everyone. I add the pictures. I now think this specimen resembles Modocia. Hmm... Link to comment Share on other sites More sharing options...
izak_ Posted December 6, 2014 Share Posted December 6, 2014 Well, first off nice buy! I agree with the seller, if he's wrong… Link to comment Share on other sites More sharing options...
rocou3rd Posted December 6, 2014 Author Share Posted December 6, 2014 This specimen hid his cheek spine, when he became fossil. So I and the dealer misunderstand him. By the way, my country's proverb says,'A clever falcon hides his claws.' it means that 'still waters run deep.' He is very clever fossil ! Thank you! 1 Link to comment Share on other sites More sharing options...
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