Morphological Convergence in Forest Microfungi Provides a Proxy for Paleogene Forest Structure

Abstract

Amber, fossilized plant resin from gymnosperms and angiosperms, is renowned for preserving a wide range of organisms in microscopic fidelity. These so-called amber inclusions comprise many groups of organisms, ranging frombacteria to arthropods and vertebrates (Penney, 2010; Ragazzi and Schmidt, 2011;Grimaldi and Ross, 2017). Organisms trapped in amber typically derive from forest ecosystems where they became stuck to resin outpourings in their habitats (Seyfullah and Schmidt, 2015). In addition, ambers are prime examples of chemical fossils that are relatively resistant to diagenesis and can retain their original chemical and isotopic compositions. Therefore, chemical profiles of ambers may support the detection of the resin-bearing plants and the reconstruction of the paleoenvironment and paleoclimate (Langenheim, 2003; Dal Corso et al., 2017). The study of amber and its inclusions should consequently enable the reconstruction of past forest ecosystems and even prevailing climatic conditions. However, several constraints exist for this approach. Much amber from the hundreds of worldwide localities does not contain notable inclusions or predominantly preserved arthropods, prokaryotes, and fungal mycelia (Martınez-Delclòs et al., 2004; Labandeira, 2014). Arthropods are indeed the most commonly studied amber inclusions, whereas fossil plant remains and palynomorphs, on which reconstructions of Cenozoic forests and derived climate estimates are typically based on (Ferguson et al., 1998; Bruch and Mosbrugger, 2002; Kunzmann and Walther, 2012), are relatively rare in amber. Only six worldwide amber deposits harbor plenty of plant inclusions, so far: Miocene Dominican and Mexican ambers, Paleogene Baltic, Bitterfeld, and Rovno ambers, and mid-Cretaceous Burmese amber (Penney, 2010). Further hurdles are linked to the physical properties of amber. Once reworked from the original sediment, amber may float or drift in sea water, and the notion exists that even amber specimens forming large deposits may have been reworked and transported, originally belonging to older and possibly geographically distinct sediments (Weitschat and Wichard, 2010). Baltic and Bitterfeld ambers constitute the largest Paleogene amber deposits worldwide, with estimated 640,000 tons of fossil resin for the Baltic deposit (Weitschat and Wichard, 2010) and approximately 3000 tons for the central German Bitterfeld locality (Liehmann, 2013). Hundreds of thousands of inclusions were found in Baltic amber, with >3000 species described from Baltic amber (Weitschat and Wichard, 2010) and >700 species reported from Bitterfeld amber (Rappsilber, 2016). Uncertainties regarding botanical provenance, age, and geographical origin are particularly associated with these two amber deposits. Langenheim (2003) introduced the term "Tertiary Baltic Amber Mystery" to refer to the conflicting evidence about the botanical source of succinite, which is the main resin variety of Baltic

How diverse were ferns in the Baltic amber forest?

“…Our study suggests that the diversity of ferns in the Baltic amber forest was low and that at least epiphytic and climbing ferns were rare or even absent. This is generally in line with a recently suggested temperate origin of Baltic amber (Kaasalainen et al, ; Sadowski et al, ; Rikkinen & Schmidt, ).…”

“…Following the latest reconstruction of the Baltic amber forest, it was a heterogeneous landscape with coastal swamps, bogs, lowland swamps, riparian forests, and mixed conifer‐angiosperm forest, intermingled by drier and light open patches (Sadowski et al, , , , ). The climate was most likely warm‐temperate to temperate and relatively humid (Kaasalainen et al, ; Sadowski et al, ; Rikkinen & Schmidt, ), so generally favoring terrestrial ferns but not epiphytic nor climbing ferns.…”

Woodpeckers can act as dispersal vectors for fungi, plants, and microorganisms

“…Woodpecker-mediated dispersal could be especially important for rare and highly substrate-specific species, such as certain calicioid lichens (Rikkinen & Schmidt, 2018;Tibell, 1994) or aspen specialists (Gjerde et al, 2012).…”

Sareomycetes cl. nov.: A new proposal for placement of the resinicolous genus Sarea (Ascomycota, Pezizomycotina)

“…Sorocybe resinae ( Chaetothyriales, Herpotrichiellaceae ) and its synasexual morph Hormodendrum resinae ( Seifert et al 2007 ), and S. oblongispora ( Crous et al 2019 ), represent asexual Eurotiomycetes that are also often found on resin. The association of these fungi with conifer resin has existed for at least 35 M years as evidenced by fossilized specimens in Palaeogene amber ( Rikkinen & Poinar 2000 , Tuovila et al 2013 , Beimforde et al 2014 , Rikkinen & Schmidt 2018 ). While other resinicolous fungi have not received as much recent attention, a significant number occurs in other classes.…”