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Pennsylvanian Nautiloid with deep umbilicus


BobWill

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I found this partial nautiloid at Jacksboro. Finis Shale member, Graham Formation, Pennsylvanian. The odd part is how deep the umbilicus is. There was just enough of it to see a piece of intact inner whorl for the profile and some septa to know about how much bigger it could have been if an adult. There was also a piece of the flank broken back with tubercles. I made the clay model of what it might have looked like whole but left off most of the tubercles. I will add photos comparing it to a Metacoceras fragment of about the same diameter that shows the depth from the flank to the previous whorl being about twice as wide.

IMG_20210131_215126180.thumb.jpg.f948e7c12a79c034ce86b6078c8a2c32.jpgIMG_20210131_215314527.thumb.jpg.235594f2ceec9035f9259ec3619d4c33.jpgIMG_20210131_215418980.thumb.jpg.8f2af6b4fabebbbd07f7c00ca47ca080.jpg

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You can see here the Metacoceras on the left has less than half the width of the umbilical wall as the unknown specimen. A similar sized Tainoceras is about the same as the Metacoceras.

 

IMG_20210131_220002414a.jpg

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