Abstract

The spores of arbuscular mycorrhizal fungi (Glomeromycota) in the Early Devonian Rhynie ecosystem served as a habitat for a diversity of other fungi, only a few of which have been studied in detail so far. Rhizophydites shutei nov. sp. occurs in planar assemblages and tuft-like clusters comprised of thalli in various stages of development on Archaeosporites rhyniensis-like acaulospores. The presence of multiple individuals on several closely spaced hosts allows a thorough depiction of this fungus. Thalli are monocentric and characterized by an ovoid, narrowly to broadly citriform, bulb-shaped, or globose inoperculate zoosporangium 10–35(–38) μm high and 7–33 μm wide, and an endobiotic rhizoidal system reaching into the host lumen. The sporangium can be epibiotic or interbiotic (stalked), or located between the wall layers of the host spore. Mature sporangia have a pronounced apical papilla. Similarities with the modern chytrid genera Rhizophydium and Phlyctochytrium are used to suggest that the fossil belongs to the Chytridiomycota, and to place it in the genus Rhizophydites, which accommodates chytrid-like fossils that are morphologically similar or even identical to present-day Rhizophydium. This discovery contributes to our understanding of the various roles mycorrhizal fungi had in early terrestrial ecosystems.

Key words

apophysis, discharge papilla, Glomeromycota, Early Devonian, rhizoidal system, Rhizophydium, zoosporangium

Abstract

Uncalcified macroalgae are generally rare as fossils, and hence their past diversity and evolutionary history remain poorly resolved. The Bolca area in northern Italy has yielded abundant adpression fossils of Eocene macroalgae. However, the vast majority of specimens are detached blades and blade portions. Here, we present an almost complete thallus of the macroalga Pterigophycos from Bolca that consists of a squat holdfast from which leaf-like blades up to 30 cm long extend. Each blade has a midrib extending over its entire length. Proximally the lamina forms a narrow rim on each side of the midrib, but becomes wider and lobed in the lower mid-portion. In the upper three quarters of the blade the lamina consists of spathulate or wedge-shaped segments. Pterigophycos blades have certain features in common with the present-day Phycodrys rubens, Delesseria sanguinea (both Ceramiales, Rhodophyta), Undaria pinnatifida, and Egregia menziesii (both Laminariales, Phaeophyceae); however, the systematic affinity of the fossil remains unresolved. The fossil is suggestive of intraspecific variability in blade morphology, and thus contests the historic view that there are several different species of Pterigophycos in the Bolca flora.

Key words

holdfast, Rhodophyta, thallus, uncalcified macroalga, Lessini Mountains, Ypresian