Unique myxomycete fossil found in Cretaceous amber

An international team of scientists from the universities of Helsinki, Göttingen and the American Museum of Natural History in New York has now discovered the oldest fossil of a myxomycete known to date. The 100 million-year old amber fossil opens a window into evolution of complex Amoebozoans.

The newly discovered fossil from amber of Myanmar is ca. 100 million years old. What surprised the team most is the fact that fossil is readily assignable to a genus of myxomycetes that still lives today. 

“The fossil provides unique insights into the longevity of ecological adaptations in myxomycetes,” says Alexander Schmidt from Göttingen University. 

“We interpret the morphological stasis as evidence of strong environmental selection favoring the maintenance of adaptations that promote wind dispersal of their minute airborne spores,” Jouko Rikkinen from Helsinki University explains. The ability of myxomycetes to develop into resting stages, which can last years, likely also accounts for the striking similarity between this fossil and its living relatives.

Finding myxomycetes as fossils is extremely unlikely, even in amber, as their fruiting bodies are ephemeral. The paleontologists are fascinated by the likely chain of events that once lead to the preservation of the fossil slime mold. 

“The fragile structure seems to have been detached from tree bark under the foot of a lizard struggling from its entrapment in viscous resin, before ultimately being overwhelmed by the exudate and preserved together with the myxomycete,” Rikkinen adds. The reptile detached the fruiting bodies at a rather early stage with spore mass not yet released, this now opens a rare window into evolution of these enigmatic organisms.

Would you know what a myxomycete or ‘slime molds’ is?

If one thinks about fossils preserved in amber, fossilized tree resin, probably insects and spiders come into mind. But what scientists report in the journal Scientific Reports is something completely different and perhaps somewhat mysterious: a myxomycete. 

Myxomycetes belong to the so-called Amoebozoa. They are microscopic organisms that live as single motile cells for most of their time in soil and decaying wood, feeding on bacteria and other minute organisms. But they can aggregate to form highly aesthetic multicellular spore-bearing fruiting bodies for reproduction. 

One obstacle hindering studies of myxomycete evolution is the fact that their fossils are exceedingly rare. Only two reliable specimens of their fruiting bodies were previously known as ca. 35 to 40 million-year-old fossils.

Original publication: 

Rikkinen, J., Grimaldi, D.A. & Schmidt, A.R. 
Morphological stasis in the first myxomycete from the Mesozoic, and the likely role of cryptobiosisSci Rep 9, 19730 (2019) doi:10.1038/s41598-019-55622-9