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Showing results for tags 'cyphaspis'.
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Day Two ; Locality One (or Six if you include Day One) Black Sahara, South of Erfoud 20th February 2019 Well this is where things really get interesting, so stick with this thread as there are dozens of photos of fossils coming up. Looks at the tags if you want clues. I was up bright and early and wandered out at about 7 am to watch the sun rise over the still mighty Erg Chebbi dunes. And as night's candles were burnt out and jocund day stood tiptoe over the misty duney tops, the chaps came to join me and managed lots of photos. Here's one, if you would like to see more, I'm busy posting a kazillion of 'em under the Nature Photography thread.
I know back home people are fond of prep stories, so I though it would be nice to present one here. It is an ongoing preparation, so any progress, ...or any problem with the specimen, error from my side, etc.. will be reported almost live (I'm already a bit further, so I have to catch up a bit here). The specimen is a Cyphaspis trilobite from the El Otfal formation in the Moroccan Ma'der basin, which I found on my last trip there. The first pic shows the specimen as found: as a nice cross-section in solid limestone. You can recognize the head ('cephalon') to the left, and several segments to the right. The cephalon cross section shows a wide cephalic border and the large glabella with numerous tubercles, both very typical for this genus. Some Cyphs from this couche are known to have 4 characteristic spines or thick tubercles on the glabella. It is good to know or suspect such features beforehand. It is easy to damage such features when you're not expecting them. In this case however, there is considerable variation in these features, so the exact shape, location and dimensions of the spines were a surprise. Therefore, I had to advance with great caution. The second picture shows the frontal view with these 4 spines exposed. So far, so good. Next, I advanced to check whether the right librigena (or free cheek) is in place. Trilobites molt by shedding these, so they are often missing or displaced. It is there, and only slightly disarticulated, which is good. The presence of the left librigena was already clear from the cross-section. Can you spot it? Interpreting these cross-sections takes some of practice. The last two pictures show the exposed right librigena and stalked eye.