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 actinomycetes, Streptosporangiopsis russelli and Paleomonospora tishomingoensis, the earliest certain fossil representatives of the Streptosporangiaceae and Micromonosporaceae, respectively. Fungal spores and hyphae of uncertain affinities are also reported. The paleoenvironment of these fossils seems to have been aquatic or semi-aquatic. The description of these microfossils is used as a base to establish principles for distinguishing true microfossils from pseudofossils in amber: true microfossils should be completely enclosed inside the amber matrix and should be comparable to living analogues, as far as can be observed, in size and cellular structure.