Natural History - Fossil 'Whitby Dac' Ammonite Nodule

Comprising seven complete and two partial Knightia alta fossil fish in a rectangular matrix. 373 grams, 15.3 x 9.8 cm

Fine condition.

Wyoming, Green River Formation, U.S.A. Acquired during the 1980s. From the Pradi Collection, Boston, U.S.A.

Seasonally, some 56 million years ago, in the Green River Region of Wyoming, torrential rains fell on the mountains. The rain flowed down the mountain sides, forming wide shallow lakes in the valley below. During the dry season, these lakes evaporated (similar to certain parts of Africa today). Millions of fish died in this short period of time. This climatic cycle happened over a 20-thousand-year period. Layer upon layer of mud was deposited over these years, entombing huge numbers of fish. At a much later date volcanic activity uplifted this area to expose their fossils.

With a composition of 92.35% iron and 6.96% nickel, classified as a nickel iron meteorite (111CD). 34.7 grams, 46 mm



From Nantan Nandan County, Guangxi Region, China. From an old Lincoln, UK, collection.

The Nantan meteorite fell in 1516, as recorded in ancient Chinese texts; the fall exploded during descent which resulted in a shower of many individual iron meteorites over an area some 28km x 8km in Nantan County, Guangxi, China. Classified as an iron meteorite; 111CD Course Octohedrite, the composition is approximately 92% iron, 6% nickel and contains more than ten other minerals including kamacite, taenite, dominate, plessite, schreibersite, triolite, graphite and others.

Displaying a fossil Knightia sp. fish. 621 grams, 15.5 cm



Acquired during the 1980s. From the Pradi Collection, Boston, U.S.A.

In southwest Wyoming (and parts of Colorado and Utah) in the Green River Formation are found some of the world's most outstanding specimens of fossil fish. The Green River system was composed of three lakes: Lake Ulinta, Lake Gosiute and Fossil Lake. These Eocene lakes lay in a series of intermountain basins formed by geological events that uplifted the Rocky Mountains during the early Tertiary time. The climate was much different from the desert-like climate of this area today. Both the fauna (crocodiles, alligators, boa constrictors and some subtropical fish families) and the flora (such as large palm trees) indicate a climate much like that found along the Gulf Coast today. Large amounts of ash found in the sediments indicate that volcanoes were particularly active at this time.