FOSSIL OF A PALM LEAF Sabalites sp. Green River... Lot 4

FOSSIL OF A PALM LEAF Sabalites sp. Green River Formation Eocene (53.5-48.5 Ma) Kemmerer, Wyoming, USA H. 76 ¾ in - L. 36 ½ in Palm fronds are fossils of great beauty, highly prized by collectors, exceptionally rare because the thin leaves usually decay. Fifty million years ago North America as far as Alaska was covered by dense, moist forests due to a tropical climate. Silent witnesses to that past are the various fossil plant species typical of warm climates found in places that are totally unsuitable today. This palm frond growing when the Rocky Mountains were still forming, some 15 million years after the extinction of the dinosaurs, is an extraordinary example.  The palms of the Green River Formation bordered a warm freshwater lake, and occasionally the fronds ended up in lakes where the anoxic waters of the lower layers were perfect for the preservation of animal and plant remains that sank there; the lack of oxygen slowed bacterial decomposition and kept the "scavengers" away. These remains were gently buried by a steady rain of calcium carbonate sediment.  Wyoming's Green River Formation is a lagerstätten, a geologic formation most famous for its remarkable fossil biodiversity, not only of fish but also of soft, delicate plant material, among the rarest in the fossil record because it begins to decompose rapidly. Lagerstätten developed under anoxic conditions in fine carbonate muds that were deposited in lake beds. The limestone matrix is so fine-grained that the fossils include fallen leaves in spectacular detail and rare soft parts of complete insects, including delicate wing membranes and spider strands. This fossil site is first mentioned in the diaries of early missionaries and explorers such as S. A. Parker, 1840, and J. C. Fremont, 1845.