Premise: The sooty molds are a globally distributed ecological group of ascomycetes with epiphyllous, saprotrophic habit, comprising several phylogenetically distant taxa (i.e., members of the classes Dothideomycetes and Eurotiomycetes). Their fossil record extends almost continuously back to the early Cretaceous; however, they are hypothesized to have originated in the early Mesozoic. Here, we describe new specimens of sooty molds associated with conifer leaves from Jurassic hot spring deposits of Patagonia, Argentina.

Methods: Thin sections of chert samples from the La Matilde Formation, Deseado Massif (Santa Cruz, Argentina) were observed using light microscopy.

Results: The fungi occur on the surface and axils of leafy twigs with podocarpaceous affinities, forming dense subicula comprised by opaque moniliform hyphae. Additionally, several asexual and sexual reproductive structures are observed. On the basis of vegetative (i.e., dense subicula composed of moniliform hyphae; hyphae composed of opaque cells deeply constricted at the septa) and reproductive characters (i.e., poroconidial and sympodioconidial asexual stages and diverse spores), two morphotypes were identified with affinities within lineages of the subphylum Pezizomycotina that encompass the ecological group of sooty molds, and a third morphotype was within the phylum Ascomycota.

Conclusions: This finding extends the fossil record of sooty molds to the Jurassic and their geographic fossil range to the South American continent. In particular, their association with podocarpaceous conifers is shown to be ancient, dating back to the Jurassic. This new record provides an additional reference point on the diversity of interactions that characterized Jurassic forests in Patagonia.