Elsevier

Fungal Biology

Volume 124, Issue 10, October 2020, Pages 835-844
Fungal Biology

Fossil callimothalloid fungi: Revised taxonomy, modern equivalents and palaeoecology

https://doi.org/10.1016/j.funbio.2020.06.002Get rights and content

Highlights

  • Common callimothalloid fossil-genus Callimothallus is revised as modern Neomycoleptodiscus

  • New fossil-genus Muyocopromyces corresponding to modern Muyocopron is described.

  • Presence of the members of the family Muyocopronaceae is dated back to the late Cretaceous.

  • Geographical and stratigraphical range of callimothalloid fungi is summarised.

  • Fossil callimothalloid fungi are proposed as reliable warm climate proxy.

Abstract

This paper presents the reinterpretation of the taxonomic position of fossil epiphyllous callimothalloid fungi belonging to the fossil-genera Callimothallus (hitherto classified to the family Microthyriaceae) and Cribrites (?Microthyriales). These fungi thrived from the Late Cretaceous up to the Holocene. Investigation are based on collected material from the Oligocene of Hungary and the Miocene of Poland and on published data. For the common callimothalloid fungus Callimothallus pertusus, a new combination Neomycoleptodiscus pertusus is proposed. Callimothallus quilonensis is assigned to a new fossil-genus Muyocopromyces as a new combination Muyocopromyces quilonensis. We reconsider the fossil-species Ratnagiriathyrites hexagonalis as a younger synonym of the fossil-genus Cribrites. The geographical range of fossil callimothalloid fungi and their recent counterparts are discussed. Fossil Neomycoleptodiscus, Muyocopromyces, and Cribrites are proposed as reliable climate proxy of warm climate conditions in the past.

Introduction

Fungi are one of the kingdoms of eukaryotic organisms that probably appeared in the late Proterozoic (Taylor et al., 2015). In the fossil state fungal hyphae, sporocarps, and spores are usually found as coalified compressions and permineralizations, rarely also as impressions and even casts. Well-preserved fungal remains, sometimes almost unaltered are found embedded in amber (Halbwachs, 2019) and are common in palynological samples (Elsik, 1996; Worobiec et al., 2009). An important group of fossil fungi are epiphyllous fungi found both on cuticles of fossilised leaves and as detached specimens during palynological analysis. Most of the fossil epiphyllous fungi usually found as sporocarps are classified as members of the order Microthyriales or in the families Asterinaceae, Microthyriaceae, Micropeltidaceae, and Trichothyriaceae (Cookson, 1947; Elsik, 1978; Tripathi, 2012; Worobiec and Worobiec, 2013). The taxonomy of fossil epiphyllous fungi is generally based on morphological features. However, they are usually preserved as sporocarps alone without any asci, ascospores, and attached mycelium. This makes the taxonomy of fossil epiphyllous fungi especially difficult since only few diagnostic features are available. Molecular phylogenetic approaches are generally not applicable for the taxonomy of fossil species since DNA is not preserved in specimens estimated to be several million years old. Considering these limitations, similarly to many groups of fossil organisms, the taxonomy of fossil epiphyllous fungi is based on an artificial morphological taxonomic system (Elsik, 1978). The determination of the generic position of epiphyllous fungi in many cases has led to serious mistakes (e.g. García-Massini et al., 2004 see section “Ecology and climatic inferences of callimothalloid fungi”). Fossil fungi, however, could be useful as a palaeoecological proxy (Dilcher, 1965; Lange, 1976; Elsik, 1978; Bera and Mandal, 2014; Conran et al., 2016; Worobiec and Worobiec, 2017; Worobiec et al., 2018) and recently fossil fungi have also been applied for the calibration of phylogenetic trees obtained using molecular clock methods (Beimforde et al., 2014; Hongsanan et al., 2016; Liu et al., 2017) assuming that they are exactly dated, well preserved allowing identification, and can be assigned to modern taxonomic groups. We conducted a detailed investigation aimed at the taxonomic revision of the remains of epiphyllous, so far enigmatic callimothalloid (with sporocarps bearing porate cells) fungi, which have usually been considered to be the representatives of the family Microthyriaceae (Dilcher, 1965) or the order Microthyriales (Kalgutkar and Jansonius, 2000). They are frequently reported both during palynological investigations (Kumaran et al., 2001) and on the cuticles of fossil leaves (Du et al., 2012) in Upper Cretaceous up to Holocene deposits. We reinterpreted the taxonomic position of the fossil-genera Callimothallus Dilcher ex Janson. and Hills and Cribrites R.T. Lange and fossil-taxa described under these fossil-genera. This is followed by a discussion on recent counterparts and the palaeoecological significance of these fungi. The study of fossil callimothalloid fungi is based on collected material from the Oligocene of Hungary and the Miocene of Poland (Callimothallus pertusus Dilcher) and on data published (C. pertusus, Callimothallus quilonensis K.P. Jain & R. Gupta and Cribrites).

Section snippets

Geological setting

The investigation of the fossil-species C. pertusus is based mainly on specimens collected from two European localities: the Oligocene deposits of Csolnok, Hungary and the lower and upper Miocene deposits of the Bełchatów Lignite Mine, Poland. Remains of Callimothallus were found both on cuticles isolated from leaf compressions and in palynological samples.

The Hungarian locality, Csolnok (47°41′37″N 18°42′18″E), is situated in the Dorog Basin, N Hungary, important for mining of brown coal of

Taxonomy

Dothideomycetes.

Muyocopronales Mapook, Boonmee & K.D. Hyde (2016).

Muyocopronaceae K.D. Hyde in: Hyde et al. (2013).

Neomycoleptodiscus Hern.-Restr., J.D.P. Bezerra and Crous (2019).

Type species. Neomycoleptodiscus venezuelense Hern.-Restr., J.D.P. Bezerra and Crous (2019).

Fossil-species. Neomycoleptodiscus pertusus (Dilcher) G. Worobiec, comb. nov. Plate 1.

MycoBank number: MB 836230

Basionym. Callimothallus pertusus Dilcher, Palaeontographica B 116 (1–4): 13.1965. Jansonius and Hills, Fossil

Conclusions

The commonly recorded fossil callimothalloid fungus, Callimothallus pertusus, previously thought to be related to the fungal family Microthyriaceae or to some modern algae (Phycopeltis and Ulvella), is found as almost identical to the modern Mycoleptodiscus disciformis and N. venezuelense. To accommodate fungal remains of the C. pertusus type a new combination is proposed, Neomycoleptodiscus pertusus. Contrary to C. pertusus, another fossil callimothalloid species C. quilonensis has pores found

Acknowledgements

This work was supported by the W. Szafer Institute of Botany, Polish Academy of Sciences, Kraków, Poland through the statutory funds to Grzegorz Worobiec and Elżbieta Worobiec, and by the National Research, Development and Innovation Office (NKFIH-OTKA 120123) and German Academic Exchange Service (DAAD) to Boglárka Erdei. Dr. Marie-Stéphanie Samain (Editor, Acta Botanica Mexicana), Dr. Vandana Prasad (Director, Birbal Sahni Institute of Palaeosciences) and Dr. Amit K. Ghosh (Editor, The

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