What type of bivalve and what type of environment?

[DinoLily]

Hello, can you help me ID these bivalve? They are from the Lance Fm in eastern WY (Late Cretaceous). I'm sorry the pictures are not pristine. They are old and I do not currently have the shells with me to take new ones. Also, does anyone have any idea whether I can determine if they are aragonitic or calcitic at this point?

Thanks!

[Peat Burns]

Those are really nicely preserved! I can't help on identity, but would assume freshwater, obviously, being from the Lance. I think I have a paper somewhere that might be helpful. I'll try to remember to look in my files tonight.

[abyssunder]

I agree with Peat Burns, although I'm not familiar with the bivalves of your area. My first thought was freshwater bivalves. So, with the strengthened ID, I guess, they could be close to the Unio genus.

[Herb]

maybe pieces of Inoceramus sp.

[doushantuo]

Lance:

http://pubs.usgs.gov/bul/1917i/report.pdf

[doushantuo]

BTW,I agree with Abyssunder ,definite unionid feel to those bivalves

[old dead things]

You don't list where you are from in Wyoming, but I'd take them to the Tate Museum in Casper, or the museum on the Western Wyoming campus in Rock Springs for an identification check. I'm sure FF member JPC could help you at the Tate. Also if you are in the Torrington area this weekend (June 25-26), stop by the state rock, fossil and gem show, lots of dealers there that could help you.

Welcome to the Forum.

[Ridgehiker]

Aragonite or calcite? Both are polymorphs and can be in the same shell. There are some specific tests ( not readily available) but I'd guess these shells are primarily aragonite. If you wet the shells and tilt them at various angles in the light, aragonite will tend to reflect more evenly. Calcite more angular.

They look like Unios but I'll defer to others. The issue throughout the Western interior is that the Cretaceous inland sea expanded and contracted repeatedly so one gets alternating layers of marine and non marine shells. Also, a lot on terrestrial fauna was preserved in flood areas of river estuaries where they entered the sea.

An aside. When I'm out trekking around a new area, I'm usually first looking for shell layers rather than Dino material. They are easier to spot ( white, sun reflecting, etc). Then I'll look for Dino material and other vertebrate specimens in among or nearby the shell layers. The two often go together. This is especially the case in Oldman Formation in Lost River, Alberta and the Hell Creek Formation north of Jordan, Monana.

Edited June 24, 2016 by Ridgehiker