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This is a lot of small fossil shells from Florida, many of these are extinct. These have a very special quality, in that they are fluorescent under a 365 nm UV blacklight. Whereas under normal light they are completely white, the fluorescence reveals their original shell pattern! This is a rare phenomenon, in my experience with fossil shells less than 25 % have this quality. It is not entirely known why some have this, but sometimes it seems that those more likely to have it have been re-exposed from their sediments and subjected to the light of the sun for an extended period of time. This is not always the case, though, so does not explain the phenomenon completely.
It is important that the blacklight you use has 365 nm UV range and has a low white light component. I recommend the Darkbeam brand on Amazon.
The locality of these specific shells is not precisely known, but these will likely be from the Caloosahatchee formation which spans the boundary of these pliocene and pleistocene ages (1.8 to 2.5 million years ago)
This was a period before the last ice age, and Florida was mostly shallow ocean as the water level was so high (hence these deposits are found far inland today). The land and sea then had many species we would feel were familiar, but most of which are now extinct. In the sea this included sea cows (dugongs), various seals and sea lions, whales, many corals and fishes, and many sharks (sadly megalodon was gone by this period). On the land there would have been Mammoths and Mastodons, Giand sloths and Giant armadillos, Glyptodonts, and Saber toothed cats as well as dire wolves. The period of the Caloosahatchee formation was a time well before humans came to Florida, and indeed according to the fossil record, before humans existed. No Human would have walked the shoreline and picked up the extinct species here.
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