|The herring Knightia and palm frond|
Formation: Green River Formation
Age: Eocene (50 Ma)
If England and Scandinavia had tropical climates in the Eocene, it should come as no surprise that North America was quite a bit hotter as well. Perhaps the best evidence for this comes from localities in Wyoming, and no Equality State fossils are more spectacular than those of the Green River Formation. Palms and crocodiles, many of them spectacularly large and all of them impeccably preserved in the sediments of a series of ancient lakes, attest to the warm, wet climate of what is now an arid landscape. Fossil Lake has also yielded impressive bird and mammal specimens, including the earliest bat, but the stars of the show are fish. Literally millions have been uncovered from the shales of southwest Wyoming, ranging from herring and perch to gar and paddlefish and including taxa as exotic as stingrays. The overwhelming numbers of fish fossils from the Green River Formation mean that they have become common sights in museums, rock shops, and personal collections across the world and making Fossil Lake perhaps the most familiar of all lagerstätte.
Visit: Fossil Butte National Monument near Kemmerer preserves some of the most important Green River localities and has an excellent visitor center. Several privately-owned sites in the area allow fossil collection (usually for a fee, and remember that poaching fossils from private or public land is a sure ticket to paleo hell).
Fossils: I doubt there is a natural history museum on North America without a Green River collection. The best, and largest, display I've seen is at the Field Museum.
Is there a book full of gorgeous fossil photos that I can gift to a paleontologically-minded friend?: There is! And, as a subtle hint to my family and friends, this is one of the few books on Cenozoic lagerstätten that I don't own.
This post is part of my 2015 Paleontology Advent Calendar, a series of vignettes on lagerstätten - sites of exceptional fossil preservation - that document changes in climate and environments through the Cenozoic. You can see the other posts here.