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andyrice11 posted a topic in Fossil IDThis post is about a well preserved Gravicalymene celebra molt I recently found in the Laurel member of the Salamonie formation of Southeastern Indiana. It is quite a peculiar specimen since it appears to have two very distinct mineral compositions. Most of the trilobite is composed of dolomite as is typical for fossils found in the Laurel. However, I initially noticed what appeared to be white calcitic pieces of the cephalon partially exposed at the anterior end of the specimen. The matrix surrounding these pieces was very easy to remove, having a fine sand like consistency. After some prep work, I was able to uncover a good portion of the glabella and concluded that these white pieces did indeed belong to the same specimen. My initial thought was that they are composed entirely of calcite, but I haven't been able to make that conclusion so I decided to post some detailed pictures in order to see what you all think. Figures 1&2. Specimen in ventral and lateral views. (Before prep work, the white rostral plate and lateral border (cephalic doublure?) which are quite obvious in the above picture, were only partially exposed. Initially my professor suggested that they likely belonged to a separate fossil specimen, perhaps a bryozoan.) Anterior end Figure 3. Anterior view showing the left and right lateral borders (cephalic doublures?), rostral plate and patrially exposed glabella. Figures 4&5. Magnified images of the rostral plate displaying uniform bumpy texture on the surface. \ Figure 6. Magnified image of dolomitized lateral border (cephalic doublure?). Note the absence of the bumpy texture seen in the previous images. So essentially my main questions are: 1. Could this white colored mineral be calcite, or something else? 2. Are the long narrow pieces considered cephalic doublures or just lateral borders? (In my research, I haven't been able to find a detailed description of Calymenid cephalic anatomy) 3. What exactly are the uniform bumps found on the white pieces? 4. Is double mineralization of a single specimen a rare occurrence, or has anyone seen something like this before? 5. What could this mineralization mean in terms of the taphonomic interpretation of this specimen. An interesting side note: A few weeks later I was once again fossil hunting in the spot at which I found the specimen described above. Along with some nice brachs and another full trilobite, I found a partial mold of a G.celebra thorax. I looked and looked for the specimen it may have once been attached to, but was unable to find anything. After returning to my lab, I noticed something quite interesting. It turns out that the mold belonged to the specimen I had collected just a few weeks before! I was glad to have found this mold, since it shows the morphology of part of the specimens posterior half which has been weathered away. Figure 7. The partial mold Figure 8. Specimen and mold side by side. Figure 9. Reunited and it feels so good!
I'm a newbie fossil hunter and I live in Jessup along rt. 1 I've seen some discussions about questionable sites but none specify the exact area to look. In the woods out back there is a stream called Dorsey Run with TONS of pebbles and such in it and the stream runs along rt 1 and does cross under rt.1 near Assateague rd. I'm not sure much of the geology of the area but I've read there are dinosaur fossils in the Jessup/Laurel area. I've been back there to glance to see if I can find anything but nothing turns up at first glance. When it gets warmer maybe I'll search more extensively in that stream. I've also read there are shark teeth in Laurel's Prince George's County area but still cant find details on the location. Does anyone in the area know of any fruitful sites to check?