Divergence time calibrations for ancient lineages of Ascomycota classification based on a modern review of estimations

Inaccurate taxonomic placement of fossils can lead to the accumulation of errors in molecular clock studies and their generated evolutionary lineages. There are limited fossil data that can be used in divergence time estimations. Therefore, reliable morphological characterization and taxonomical identification of fossil fungi are extremely important. Most fossils of Dothideomycetes and Sordariomycetes are from the early Cenozoic (66-23 Mya), with fewer from the late Mesozoic (174-145 Mya). However, it is hard to distinguish some fossil descriptions as photographs and illustrations are unclear; thus, the validity of using these fossils in calibrations of molecular clocks is problematic. This study brings scattered paleobiological data on selected fossil Ascomycota, using descriptions, fossil images and illustrations, coupled with recent age estimations, and taxonomic and phylogenetic affinity of extant species. As an integrated approach, this study summarizes a historical fossil outline with a reliable minimum age for 16 calibrating points viz. crown of Aigialus, Anzia, Aspergillus, Asterina, Calicium chlorosporum-C. nobile, Capnodiales, Chaenotheca, Colletotrichum, Diaporthales, Meliola, Ophiocordyceps, Microthyriales, Microthyrium, Muyocopron, Pezizomycotina and Stigmatomyces. A scheme of Ascomycota ancient lineages is also provided in order to improve divergence time estimations.