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Agate Snails from Lahontan Formation, Miocene

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I have a couple of new fossils I need identified. By my guess they are Ammonites but what do I know? I'm fortunate that these snails come with some identification, a small piece of paper with some handwriting on it. From top to bottom, it says "Large Agate Snails, viviparous, miocene, Lahonten Formation, Black Rock Desert, Winnemucca, Nevada." I'm a little confused because from what I've read, Lake Lahonten did not exist during the Miocene epoch. The smaller snail is about 2½ cm (1") long, from top to bottom in the picture, and the larger snail is about 3 cm (1½") long. Is there anything anyone can tell me about these pieces? Those measurements don't include the concretion attached to them. 

Fossil ~ Agate Snails Pic1 Top.jpg

Fossil ~ Agate Snails Pic2 Bottom.jpg

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  • Fossildude19 changed the title to Agate Snails from Lahontan Formation, Miocene

No ammonites at all, but very nice gastropods.

The ammonites disappeared about 65 MY ago, at the end of the cretaceous period at the same time than the dinosaurs.

Your gastropods look like some of the ones we can find here in the south-west of France, so i'll say that they might be from the Burdigalian or Aquitanian.

Also, you can check this site : http://www.fossilshells.nl.

And that site, where you can see Viviparous sp. snails : http://inyo2.coffeecup.com/fossilvalley/fossilvalley.html.

Here is one of their photo, their comment says :

"Freshwater gastropods and a pelecypod from the middle Miocene Esmeralda Formation, Fossil Valley, Nevada. For perspective, the specimen at lower right (marked with letter A) is 30mm long. Photographed by author. Collected before Fossil Valley became a federally protected area; unauthorized collecting there is now strictly verboten.

All gastropods, except specimen marked letter "D." Letter A--Viviparus sp.; Letter B (four specimens to left, and three to the right of the letter)--Goniobasis sp.; Letter C--Valvata sp.; D--A pelecypod, Sphaerium. All the rest, without lettering--Vorticifex sp."


The title of the photo is :

Freshwater Mollusks

Middle Miocene Esmeralda Formation

Fossil Valley, Nevada


  • I found this Informative 1
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Indeed, gastropods, very pretty too! :)

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I think fifbrindacier has it.

Note the spelling of Viviparus.

Ammonites and snails are not the same thing. Snails are called gastropods in more technical context, and ammonites are a type of cephalopod (which also includes octopus, squid, nautilus, etc).

Also I think the word you're looking for is 'matrix' (the sedimentary rock around a fossil). A concretion is a (generally) round nodule that is harder than the matrix around it. Fossils can occur inside concretions.


Very nice specimens.

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