MSirmon Posted April 28, 2016 Share Posted April 28, 2016 Found this in a stream bed near Enchanted Rock north of Fredericksburg Tx. Any help would be appreciated. Link to comment Share on other sites More sharing options...
MSirmon Posted April 28, 2016 Author Share Posted April 28, 2016 Here are some more angles. Link to comment Share on other sites More sharing options...
JohnJ Posted April 28, 2016 Share Posted April 28, 2016 Part of an ammonite. The human mind has the ability to believe anything is true. - JJ Link to comment Share on other sites More sharing options...
BobWill Posted April 28, 2016 Share Posted April 28, 2016 (edited) Yes, the two views in the second post show a septum in the first picture and sutures in the second. The wavy lines are the sutures which mark where other septa attached to the inside of the shell wall. The fossil may be worn down slightly past the actual sutures but the fossil is an internal mold since the outer shell would have obscured these details. The septa are the walls that separate the chambers inside the shell. The ammonite would have drained the water out of the chambers to achieve buoyancy for swimming. The present-day Nautilus is the only extant cephalopod with this kind of external shell that shows us how this worked. A much larger chamber, missing from your fossil, would have held the body. The whole shell was a coiled up cone like a snail, with the animal's tentacles extending out the large end through the aperture. The "V" shaped notch is where a turn, or whorl, overlapped the previous whorl so the cross section wasn't a true cone. Edited April 28, 2016 by BobWill 3 Link to comment Share on other sites More sharing options...
MSirmon Posted April 28, 2016 Author Share Posted April 28, 2016 Thanks Guys. I started out thinking it was ammonite related based on the suture marks but talked myself out of it. Link to comment Share on other sites More sharing options...
Uncle Siphuncle Posted April 28, 2016 Share Posted April 28, 2016 Compare with Engonoceras. 1 Grüße, Daniel A. Wöhr aus Südtexas "To the motivated go the spoils." Link to comment Share on other sites More sharing options...
Guguita2104 Posted April 30, 2016 Share Posted April 30, 2016 Ammonite fragment, for sure. Link to comment Share on other sites More sharing options...
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