Sunday, May 4, 2014

Fossils in the St. Peter Sandstone 2: actual fossils

I'm not quite sure why, but "Fossils in the St. Peter Sandstone" is one of the more popular posts to date. Who am I to argue with the St. Peter Sandstone? Last fall I visited the paleontological collections of the University of Minnesota and took a number of photos. I've received permission to post examples (thank you, Dr. David Fox!), and among them are a few photos of actual St. Peter Sandstone fossils, as primarily collected by Sardeson.

The first photo is of one of the few drawers of St. Peter Sandstone fossils. This is somewhat more impressive once you know that the St. Peter is present in about a quarter of the U.S., and three+ drawers at the University contain one of the very few body fossil assemblages found in that entire area. Fifteen states, and three drawers of mollusk molds and casts.

I suspect they were sand-tolerant mollusks.

Below are some examples of snail casts. The original shell material was leached out at some point, leaving being snail-shaped cavities that were later filled.

Pleurotomaria casts

Bivalves are also commonly represented in the collection. The following is a box of Ctenodonta casts, collected by Sardeson in the 1890s. It's somewhat surprising that these fossils have survived this long, given the St. Peter's reputation for falling apart after drying out.

Finally, to prove that Sardeson was not the only wizard active in Minnesota between 1890 and 1950, and apparently to satisfy my Stauffer quota (I swear I didn't realize it until I zoomed in on the card), here we have bivalve casts collected by Clinton R. Stauffer from the St. Peter.

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