Stunning fossils in sedimentary rocks reveal a new and co-oldest Early Cretaceous gilled mushroom-forming fungus

Abstract Mushrooms are mostly ephemeral and delicate structures that often decay without becoming part of the fossil record. Their fossils are thus rare and have been mostly found in amber inclusions, while those pressed in sedimentary rocks are even rarer. Furthermore, description of mushroom fossil species is regularly based on a single specimen where the macromorphology is often compromised by taphonomic processes, and its microstructures are scarcely assessed. Here, for the first time, 14 well-preserved fossilized mushrooms in sedimentary rocks provide a trove of macro- and micromorphological and ultrastructural traits depicting a unique and robust concept of one new fossil species. Edaphagaricites conicus gen. nov. et sp. nov. produced distinct, probably terricolous, lamellate pileate-stipitate basidiomata with a russuloid/lactarioid form habit, with a short and robust, pointing stipe and pileus trama including a dense layer of cellular structures recalling sphaerocysts. This represents the most complete fossil record within the Agaricomycetes to date, and the combination of morphocharacteristics provides evidence for its classification in Russulales fam. Russulaceae. Based on shapes, dimensions, and textures consistently preserved throughout the fossils, the way they were pressed, and their post-break pattern, 3D modelling tools were instrumental in reconstructing a probable appearance of an E. conicus fresh basidiome, also considering the affinity with Russulaceae. Our findings elucidate not only morphological but also evolutionary aspects of an ancestral Russulales fam. Russulaceae taxon. The new fossil species dates to the Aptian, and thus is considered the co-oldest mushroom-forming fungus with Gondwanagaricites magnificus and may serve as the first calibration point for divergence-time estimations of Russulaceae/Russulales within the Fungi tree of life.