Abstract

Documented evidence of root nodules in fossil plants is exceedingly rare, and thus the evolutionary history and paleobiology of these specialized structures hosting symbiotic microorganisms continue to be largely unresolved. Here we report adpression fossils of slender roots from the ~237-million-yr-old Madygen Formation in Kyrgyzstan, to which are laterally attached spheroidal protuberances up to 2.5 mm in diameter that we interpret as root nodules based on spatial arrangement and comparisons with other fossil and extant root nodules, along with several types of other plant structures exhibiting a superficially similar appearance (e.g., fertile organs, rhizome tubers). The producer of the roots and the biological nature and affinities of the microorganisms inhabiting the nodules remain unknown. The Madygen fossils are nevertheless significant because they represent the second-oldest record of root nodules worldwide, predated only by permineralized mycorrhizal root nodules from the Triassic of Antarctica.