Abstract Detail

Paleobotany

Le Renard, Ludovic [1], Berbee, Mary [1].

Comparative anatomy and phylogeny of fossil Callimothallus and their living relatives.

The fossil record of microfungi on leaves is rich. In our research, we are applying direct comparison with clades of similar extant fungi to interpret the significance of the fossils. The fossil genus Callimothallus is represented by hundreds of specimens, the earliest at least 66 million years old. A first step has been to estimate the phylogeny of Callimothallus’s likely extant relatives among the fly-speck fungi, all of them in the class Dothideomycetes (phylum Ascomycota). We use four-locus data from 65 species and a phylogenomic dataset of 101 Dothideomycetes. We then use parsimony analyses of 13 morphological characters to place Callimothallus fossils into the phylogeny of living fungi. In all of our analyses, the fossil Callimothallus corralesense appeared most closely related to Muyocopronales. Equally parsimonious solutions suggest the fossil could represent a stem lineage or a number of different crown clades within Muyocopronales. Like Callimothallus fossils, asexual morphs of Muyocopronales most frequently produce cells aggregated in a plate-like scutellum, each cell bearing a distal, raised pore for conidiation. Variation within single samples of asexual morphs points to their morphological plasticity. If porate cells of an asexual form are organized variously in irregular aggregates or in radiate scutella, we score the character as polymorphic. Radiate scutella of asexual and sexual morphs resemble one another but were never found in the same specimen. Using type specimens of Muyocopron species, we show that taxa described from radiate, sexual morphs without raised pore, may also bear pores for conidiation. While C. corralesense appears most closely related to asexual Muyocopronales that produce conidia from radiate plates of hyphae bearing small pores, our dataset accounting for polymorphic character states and porate sexual scutella adds additional, equally parsimonious placement for the fossil. Interpreted as an ancient, asexual morph of Muyocopronales, the fossil Callimothallus corralesense from the Maastrichtian of Colombia (72–66Ma) provides the earliest evidence for characters found in three different genera that diverged after the origin of the order Muyocopronales. By linking the fossil age to a living clade, we contribute a rigorously analyzed calibration point towards estimates of geological age of Ascomycota.

1 - University of British Columbia, Botany, 3529-6270 University Boulevard, Vancouver, BC, CANADA

Keywords:
Paleomycology
comparative anatomy
fly-speck fungi.

Presentation Type: Oral Paper
Session: PL2, Paleobotany: Cookson Student Presentations - Session II
Location: /
Date: Monday, July 19th, 2021
Time: 1:00 PM(EDT)
Number: PL2003
Abstract ID:860
Candidate for Awards:Isabel Cookson Award