In the early Eocene, the Green River Formation was a great subtropical lake set in a forested volcanic terrain and rich with living organisms. It is now a harsh and sparsely populated upland desert in southwestern Wyoming, but that early wealth of life has been spectacularly well preserved in the fossil record; the fish, for example, with their black or dark brown bones and scales, can be found in museums and private collections worldwide, and each is a treasure. More than a million have been found to date, and there are many more kinds of fossils, too. As Lance Grande notes in this enchanting book, the formation’s Fossil Butte Member (FBM) “provides the most comprehensive picture of Eocene life that we know of, surpassing even the beautifully preserved assemblages of the middle Eocene Messel Formation in Germany and the late Eocene Florissant Formation in Colorado”.
The Lost World of Fossil Lake is a splendidly illustrated compendium on these c.52 million-year-old fossils, written with grace and authority. Collections have been made from the site for about 150 years, and although the ma- terial has been described in many publications, there has been no comprehensive survey until now. And here it is, and with its 243 fine colour plates, it will appeal to both amateur and professional geologists and palaeontologists.
We begin with the formation’s origin and history. The great Western Interior Seaway, which in late Cretaceous times had divided North America in two, had by this time been replaced by dry land and by the Green River lake complexes, of which Fossil Lake was one of three, on the borders of Wyoming and Utah. Although this particular lake lasted less than 2 million years, its aquatic biodiversity was far greater than that of any of the others in the complex, probably owing to the number of habitats represented, and its sedimentology and stratigraphy are properly documented.
Grande next offers a fascinating tale of the early collectors, commercial and otherwise, who worked in these wild lands, with some of the former living decidedly marginal existences. This captivating story of discovery and controversy is followed by short and simple discourses on the preparation and classification of fossils. Ensuing chapters consider particular fossil groups, including stromatolites, arthropods (spiders, millipedes, insects of many kinds, crustaceans) and molluscs; each is beautifully illustrated.
Grande also gives a comprehensive description of the most common and sought-after of all the Fossil Lake treasures, the fishes - both the cartilaginous species (represented by the rare but amazing stingrays) and the far more numerous ray-finned fishes. All these 25 taxa are nicely illustrated, and there are several photographs documenting mass mortality levels, as well as of the greedy fellows who choked to death while attempting to eat other fish that were far too big for them!
The book also considers the abundance and distribution of the various kinds of fishes, ranging from Knightia with more than 600,000 known specimens to Esox with only one. Some are present only in particular environments, some of the fishes schooled, and particular taxa bred in the shallows. Amphibians are very rare, as are snakes and lizards, although various kinds of turtles are known from several Fossil Lake specimens. And even though birds and bats are not especially common, the FBM remains one of the best sources of well-preserved fossils of these animals anywhere in the world. Plants, too, are to be expected and indeed there are many here, from green algae to ferns, horsetails, conifers and broadleaves, some of great size, although, curiously, for some reason there are no grasses.
Finally we come to palaeoecology, and this section graphically portrays the life of the lake and its surroundings: food chains, mass mortality events and other factors affecting the life of the ancient lake, and the processes of fossilisation, thus bringing together everything that is so far known. In this, as in earlier chapters, Grande’s enthusiasm shines through, as does his wish to communicate his great passion for fossils in general and this Eocene lake in particular. He has set out his intention to inspire generations of students for palaeontology, and he has accomplished it very well.
The Lost World of Fossil Lake: Snapshots from Deep Time
By Lance Grande
University of Chicago Press, 432pp, £31.50
Published 15 May 2013