An article published in the journal “Scientific Reports” describes the discovery of the oldest identified slime mold, attributed to the genus Stemonitis. It’s a fossil mold dating back to about 100 million years ago preserved in excellent conditions within a piece of amber discovered in Myanmar. Jouko Rikkinen, David Grimaldi and Alexander Schmidt examined this fossil, very useful for reconstructing the evolutionary history of these organisms part of the mixomycete (Myxomycota) group, a little known history because of the scarcity of fossils.

Myxomycetes, also known as slime molds, are part of the large group of Amoebozoa, eukaryotic organisms still difficult to classify. They could be a group related to both fungi and the animals but that’s a classification still under discussion.

The oldest fossils associated with myxomycetes were discovered in rocks that are 750 million years old but these are rare finds because their so-called fruiting bodies have a very short life. The consequence is that the reconstruction of their evolution is difficult and the finding of this type of mold very well preserved in a piece of amber could be a great help.

The fossil object of this study was discovered in a piece of amber dated about 100 million years and therefore dating back to the Cretaceous period. The presence of a lizard leg suggests that the animal tore the fruiting bodies of a slime mold from a tree and, together with them, got stuck in the tree resin which subsequently fossilized into that piece of amber.

A surprise for the researchers came from the fact that the characteristics of the fossil slime mold indicate that it belongs to a genus that still exists called Stemonitis. Professor Alexander Schmidt, a paleontologist at the University of Göttingen, Germany, this study’s lead author, stated that this fossil offers unique information regarding the longevity and ecological adaptations of myxomycetes. Slime molds that spread very small spores using the wind have an advantage.

Slime molds are not as interesting for the public as animals of the time such as dinosaurs but they’re interesting from a scientific point of view for their role in the ecosystems in which they live. They contribute to the decomposition of dead plants and also feed on fungi and bacteria. Knowing that in the Cretaceous period there were species similar to some existing today offers some information on the ecosystems of the era in which they lived.