Natural History - Fossil Double Perisphinctes Ammonite

Knightia alta specimen on a rectangular matrix. 427 grams, 18 cm



From Wyoming (Green River Formation), USA. 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.

Comprising one long and one wider obelisk in lavender-coloured amethyst, each with bevelled edges. 118 grams total, 48-79 mm



From Brazil. Ex Mineral Imports, London, UK. Gregory, Bottley & Lloyd (Gregory's).

The horned ammonite with regularly disposed spines to the outer shell. 369 grams, 92 mm



From a Lincolnshire, UK, collection.