FOSSIL MICROORGANISMS FROM UPPER CRETACEOUS AMBER OF MISSISSIPPI

Microfossils are described from Upper Cretaceous amber from Tishomingo County, Mississippi, the first fossils from this amber. They include the oldest fossil record of the chrysomonad Dinobryon and two new acti nomycetes, Streptosporangiopsis russelli and Paleomonospora tishomingo ensis, the earliest certain fossil representatives of the Streptospora ngiaceae and Micromonosporaceae, respectively. Fungal spores and hypha e of uncertain affinities are also reported. The paleoenvironment of t hese fossils seems to have been aquatic or semi-aquatic. The descripti on of these microfossils is used as a base to establish principles for distinguishing true microfossils from pseudofossils in amber: true mi crofossils should be completely enclosed inside the amber matrix and s hould be comparable to living analogues, as far as can be observed, in size and cellular structure.