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Ammonite aptychus?


madness

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I recently hunted in the Austin Chalk (in Austin) for the first time and am unfamiliar with the fossils there. I posted another ID question for something I found and the ammonite suggestion sent me on a research mission. Now I'm wondering if something else we found was actually ammonite aptychus instead of the bivalves I thought they were. Most of the ones I saw online were MUCH smaller, but looked very similar. What do you think?

 

AC_BW2.jpg

 

I didn't bring this home so can't get any other pictures/measurements. I really need to pack a ruler in our gear! I have pretty average sized hands.

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3 minutes ago, BobWill said:

That would be too big for an aptychus. I believe it's a clam, look up Inoceramus for comparison.

And as it turns out, looks like my "ammonite" from the other ID thread is probably an inoceramus. Nice to have some consensus! I'm off to study up on these so I know better what I'm looking at next time I go into the Austin Chalk. Thanks!

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I agree with inocermid

“...whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been and are being evolved.” ~ Charles Darwin

Happy hunting,

Mason

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I agree that's a bivalve. Aptychi can get big though - I've got one from the Upper Lias (Lower Jurassic) that's 7 x 3cm.

Tarquin

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44 minutes ago, TqB said:

I agree that's a bivalve. Aptychi can get big though - I've got one from the Upper Lias (Lower Jurassic) that's 7 x 3cm.

I was pretty sure I had seen enormous ammonite fossil pictures, so figured there would be equally large aptychi somewhere (though possibly not here). Now that I've seen more inoceramid pictures, I'm better equipped to make some more educated guesses in the field.

 

Thanks everyone for all the great info. So glad I found this forum. It's really hard to ID sometimes when you don't even know where to start (as in, I'd never even seen the word inoceramid until today!).

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5 hours ago, TqB said:

I agree that's a bivalve. Aptychi can get big though - I've got one from the Upper Lias (Lower Jurassic) that's 7 x 3cm.

Wow, that is big. As I way typing that I wondered what was the biggest one found. I was thinking of what Maddness might expect to see in Texas and they are pretty rare in my experience of any size. I only have one and it's probably from a Pennsylvanian goniatite. I suppose someone should post a "show us your aptychi" topic unless it's already been done.

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