Turritella agate is the youngest fossil I currently use. The shells inside it belong to creatures who emerged millions of years after the ammonites went extinct.
I hadn’t realized that Turritella agate was a misnomer. (It took me long enough to catch the name. I was told it once briefly and it sounded to me like tarantula or tarantella…)
Apparently it was originally named after a species of saltwater snail that has a similar steeply pitched shell to the ones found in this stone. Sea snails of the genus Turritella had been previously found fossilized in agate in California and Texas. Most stones called turritella agate come from Wyoming, Colorado and Utah, which have freshwater deposits.
The fossil deposits range from sandstone to much chalcedony. (Agate is a type of chalcedony, so that part of the name gets partial credit for accuracy…) They bear large quantities of fossilized freshwater snail shells from the genus Elimia. A once flourishing species now extinct, they date from the Eocene. The beds are estimated to have been laid down 51-46 million years ago in what was then a series of shallow lakes.
They lived well after the dinosaurs died out, in a warm world where small mammals were establishing a foothold. The overbearing greenhouse gases and hot temperatures in a world almost without ice are thought to have favored small mammals more able to cope with heat, as well as reptiles.
I confess I keep having to google it in order to remember how to spell it. I really need to remember, especially since every time I do I find more sites ascribing metaphysical properties to it. That always gets me a bit cranky. I just don’t get why it can’t be awesome because it’s a slice of life from a long lost world-one with different continents and weather and creatures. How is that not cool enough?