Paleobiota of the Latah Formation

The paleobiota of the Latah Formation encompasses both floral and faunal elements preserved in temporary lacustrine environments formed between eruptive phases of the Columbia River Basalts in central to east Eastern Washington and central to north Idaho. The Latah Formation is centered around the greater Spokane area, with a western extent outcropping at Grand Coulee and the eastern margins as far southeast as the area of White Bird, Idaho. Dating of the core Spokane sites is based on the host Grande Ronde Basalts which give an age range of 16.5 to 16.1 million years ago. The Clarkia fossil beds lagerstätte site are slightly younger, being interbedded in the Wanapum Basalts Priest Rapids Member with an age constraint of 16.1 to 15.9 million years ago, or Early Barstovian in age.

The intermittent lakes were surrounded by a temperate ecosystem that was mesophytic in nature, and hosting a diverse flora with plants that are still native to the region and others now restricted to other areas of the globe. There is a small element of the flora that consists of fully extinct genera that are unique to the time and region. Based on work from sampling around Mica, Washington a diverse assembly of diatoms and algae lived in the Spokane area lakes though water conditions for growth were not ideal. The known fauna of the formation is smaller than the flora, with most taxa being insect species though one unnamed Sciuridae fossil was described in 2018, and fish belonging to the salmonid, cyprinid, and centrarchid groups are known. Preservation varies from carbonized compressions at most sites to exceptional organic preservations in some parts of the Clarkia area localities where original organic material is preserved down to living coloration and possible ancient DNA fragments. Upper layers of the Clarkia deposits have been recorded with modern fungi actively feeding on the ancient organic material of the fossils as a food source.