|Paleovespa, the Florissant wasp|
National Park Service
Formation: Florissant Formation
Age: Eocene (34 Ma)
The lagerstätten featured so far this month all date to the early or middle parts of the Eocene and, with the rare exception, indicate a global hothouse. The warm conditions of this interval were not to last, however. Dating to the very end of the epoch, Colorado's Florissant Fossil Beds are the Eocene's last bow, and suggest that temperate conditions had already become more widespread. Unlike most other sites in the advent calendar, Florissant preserves some truly massive specimens that document this climatic shift. The largest fossils from this lagerstätten are redwood trunks that are impressive in and of themselves but that, to anyone who has spent time in the modern forests of coastal California, clearly show that Florissant was no tropical paradise. Smaller plant fossils, of leaves and flowers, support this conclusion, as they represent trees such as beeches, willows, and pines. These leaves are preserved in exquisite detail, as are the arthropod fossils for which the site is known. Perhaps the most familiar of all Florissant fossils is the wasp Paleovespa, but insects from ants to dragonflies (both nypmhs and adults) to katydids have been found there, as have non-insect arthropods (most notably spiders). Was the cool, lakeside forest occupied by these animals representative of the world as a whole in the Eocene's closing years? It's worth noting that, like the Okanogan lakes of millions of years earlier, Florissant was a high-elevation site and this likely influenced its climate (its mountainous location certainly had an effect on the site's fossil record, as burial by volcanic ash was a major factor in Florissant's high quality of preservation). However, the advent of the Oligocene was nigh, and another, slightly younger, lakeside forest shows that temperate conditions were becoming ever more common even at lower elevations in this new epoch.
Visit: The fossil beds are preserved within Florissant Fossil Beds National Monument near Colorado Springs and make a long but doable and worthwhile day trip from Denver.
Fossils: The national monument visitor center has the largest display of Florissant fossils I've seen, but other local museums house specimens as well; I'm given to understand that the University of Colorado Museum of Natural History has an especially large collection.
Is there a relevant book full of gorgeous fossil photos that I can gift to a paleontologically-minded friend?: There is, and it's another one that my personal collection is sorely lacking.
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.