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Pseudogygites

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Another unidentified fossil from the Billings Shale Formation! This time, it's some kind of spiral shaped fossil. There are actually three in this one stone, and many more in other places, so they are fairly common. This fossil has a definite spiral shape, unlike the orthocone cross sections. Right now I think they are either some type of Gastropod, or a coiled ammonoid nautiloid cephalopod. Any ideas? I appreciate your help!

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Probably Gastropod but it is almost impossible to rule out ammonoid without a full specimen.

“...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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+1 for gastropod. Many of the cephalopods you will encounter in this layer will most commonly be orthocone nautiloids.

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The Billings Shale is late Ordovician in age, so far too old for any ammonites or ammonoids.  There is one coiled nautiloid (Trochlites) that pops up fairly rarely, but it is much larger than your specimens, it is very evolute (whorls barely overlap), and it has a reticulate surface ornament very different from your "spirals".  Straight-shelled (orthoconic)  nautiloids are common.  Traditionally these have been identified as Geisonoceras, but they have more recently been assigned to a different genus (in one of Robert Frey's publications, I don't recall the genus and will have to look it up).

 

A few gastropods and coiled tergomyids such as Sinuites are fairly common.   I think your "spirals" are one of those, but the preservation (or photos) does not allow for a confident  ID to genus.

 

Don

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