Abstract A new fossil mushroom is described and illustrated from the Lower Cretaceous Crato Formation of northeast Brazil. Gondwanagaricites magnificus gen. et sp. nov. is remarkable for its exceptional preservation as a mineralized replacement in laminated limestone, as all other fossil mushrooms are known from amber inclusions. Gondwanagaricites represents the oldest fossil mushroom to date and the first fossil mushroom from Gondwana.

Citation: Heads SW, Miller AN, Crane JL, Thomas MJ, Ruffatto DM, Methven AS, et al. (2017) The oldest fossil mushroom. PLoS ONE 12(6): e0178327. https://doi.org/10.1371/journal.pone.0178327 Editor: William Oki Wong, Institute of Botany, CHINA Received: March 26, 2017; Accepted: May 10, 2017; Published: June 7, 2017 Copyright: © 2017 Heads et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability: All relevant data are within the paper. Funding: This work was partly supported by US National Science Foundation grant EF-1304622 (to SWH) and EF-1205935 and EF-1502735 (to ANM). Competing interests: The authors have declared that no competing interests exist.

Introduction Exceptionally preserved fossils can shed important and unprecedented light on the history of life. Particularly remarkable deposits, known as Lagerstätten, yield fossils characterized by preservation of soft tissues that decay rapidly and which are not normally preserved. In many cases, large and important groups of soft-bodied organisms would be missing entirely from the fossil record if not for their exceptional preservation in Lagerstätten. Mushrooms, an ecologically important group of fungi in the order Agaricales, produce fleshy, gilled fruiting bodies (called basidiomes) that are rarely fossilized [1]. While certainly ancient, they have an extremely depauperate fossil record with only ten fossil mushrooms reported to date, all unique amber inclusions ranging from mid-Cretaceous to Early Miocene in age [2–8]. Here we report the discovery of a new fossil mushroom that is unique in its preservation as a mineralized replacement, and the oldest yet encountered. The specimen comes from the laminated limestones of the Crato Formation, which outcrop on the northern flanks of the Chapada do Araripe in Ceará, Brazil; a Lagerstätte famous for the exceptional preservation of its diverse Lower Cretaceous paleobiota [9–11].

Material and methods The specimen comprises a single, nearly complete mushroom preserved as a primarily goethitic replacement on a small slab (approximately 50 × 60 mm) of typical, buff-colored, millimetrically-laminated limestone from the Nova Olinda Member; the lowermost unit of the Crato Formation. It is housed in the URM Herbarium at the Universidade Federal de Pernambuco in Recife, Brazil, having been repatriated from the Illinois Natural History Survey Paleontological Collection. It was studied using a Zeiss SteREO Discovery.V20 zoom stereomicroscope with a Plan-Apochromat S 0.63x f/ Reo WD = 81 mm objective. Photographs were taken using a Canon 5D Mark III and MP-E 65 mm macro lens mounted to a Cognisys Stackshot motor rail on a copy stand. Multiple high-resolution images were then stacked using HeliconSoft’s Helicon Focus 6 and subsequently stitched together as a mosaic using Photoshop CC. Scanning electron micrographs were produced using a JEOL JSM-6060LV SEM. Nomenclature The electronic version of this article in Portable Document Format (PDF) in a work with an ISSN or ISBN will represent a published work according to the International Code of Nomenclature for algae, fungi, and plants, and hence the new names contained in the electronic publication of a PLOS ONE article are effectively published under that Code from the electronic edition alone, so there is no longer any need to provide printed copies. In addition, new names contained in this work have been submitted to MycoBank from where they will be made available to the Global Names Index. The unique MycoBank number can be resolved and the associated information viewed through any standard web browser by appending the MycoBank number contained in this publication to the prefix http://mycobank.org/MB/. The online version of this work is archived and available from the following digital repositories: PubMed Central, LOCKSS.

Discussion Fungi are ecologically diverse, geographically widespread, speciose organisms that account for the second largest group of eukaryotes [12]. Despite their global distribution and evolutionary history extending some 1,430 Ma [13], the fossil record for fungal structures other than spores is exceedingly scant with reports of mostly sexual [14–18] and asexual stages [19–23] of ascomycetes from mid-Cretaceous to Miocene ambers. The Basidiomycota contains over 30,000 extant species [24], but their fossil record—especially in the case of gilled mushrooms—is nearly non-existent due to their ephemeral nature and a strong preservational bias against their fleshy basidiomes [1–8]. The earliest report of a member of the Basidiomycota is from hyphae with diagnostic clamp connections dating c. 330 Ma from the Upper Visean (Mississippian) of France [25]. Only ten fossils resembling modern-day gilled mushrooms have been recorded to date, all from amber. The hitherto oldest fossil mushroom, Palaeoagaricites antiquus, was reported from mid-Cretaceous Burmese amber (c. 99 Ma) [6]. More recently, four unnamed mushrooms placed in the Agaricales have also been reported from Burmese amber [8]. Archaeomarasmius leggetti was recorded from Cretaceous amber (c. 90–94 Ma) from New Jersey, USA [3,4]. Most recently, Gerontomyces lepidotus was reported from Eocene Baltic amber (c. 45–55 Ma) from the Samland Peninsula of Russia [7]. Three other mushrooms, Aureofungus yaniguaensis [5], Coprinites dominicana [2], and Protomycena electra [3,4] have all been recorded from Early Miocene amber (Burdigalian, c. 16–18 Ma) from the Dominican Republic. Gondwanagaricites magnificus represents the oldest fossil record of a gilled mushroom and is the only fossil mushroom known from a mineralized replacement. The unique specimen extends the geological range of gilled mushrooms back by approximately 14–21 million years and confirms their presence in Gondwana during the Early Cretaceous. Molecular clock estimates suggest the divergence of the Basidiomycota around 500 Ma to 1.2 billion years [26] and G. magnificus establishes the earliest calibration point so far for the Agaricales, with a new minimum age of 113–120 Ma.

Acknowledgments We thank Dra. Leonor Costa Maia of the URM Herbarium for providing a URM accession number and for assistance repatriating the specimen to Brazil. SEM work was carried out in the Frederick Seitz Materials Research Laboratory Central Research Facilities at the University of Illinois. This work was partly supported by NSF grant EF-1304622 (to SWH) and EF-1205935 and EF-1502735 (to ANM).

Author Contributions Conceptualization: SWH. Investigation: SWH ANM JLC MJT DMR ASM DBR. Resources: YW. Visualization: MJT DMR. Writing – original draft: SWH ANM JLC MJT DMR ASM.