Just out @ Nature Ecology & Evolution
Fungus-like mycelial fossils in 2.4-billion-year-old vesicular basalt
Stefan Bengtson, Birger Rasmussen, Magnus Ivarsson, Janet Muhling, Curt Broman, Federica Marone, Marco Stampanoni & Andrey Bekker
Fungi have recently been found to comprise a significant part of the deep biosphere in oceanic sediments and crustal rocks. Fossils occupying fractures and pores in Phanerozoic volcanics indicate that this habitat is at least 400 million years old, but its origin may be considerably older. A 2.4-billion-year-old basalt from the Palaeoproterozoic Ongeluk Formation in South Africa contains filamentous fossils in vesicles and fractures. The filaments form mycelium-like structures growing from a basal film attached to the internal rock surfaces. Filaments branch and anastomose, touch and entangle each other. They are indistinguishable from mycelial fossils found in similar deep-biosphere habitats in the Phanerozoic, where they are attributed to fungi on the basis of chemical and morphological similarities to living fungi. The Ongeluk fossils, however, are two to three times older than current age estimates of the fungal clade. Unless they represent an unknown branch of fungus-like organisms, the fossils imply that the fungal clade is considerably older than previously thought, and that fungal origin and early evolution may lie in the oceanic deep biosphere rather than on land. The Ongeluk discovery suggests that life has inhabited submarine volcanics for more than 2.4 billion years.
The deep biosphere, hidden beneath land and sea, represents a major portion of life’s habitats and biomass on Earth1. In spite of significant discoveries from scientific ocean drilling and metagenomics, the deep biosphere remains largely uncharted and its geological history almost entirely unknown. The deep habitats are protected from most of the hazards of surface life, and the deep environments would have been potentially available to life from the early stages of Earth’s history. Here, we report filamentous structures preserved in carbonate- and chlorite-filled amygdales and fractures in basaltic lavas of the 2.4-Gyr-old Ongeluk Formation, South Africa. Their morphology, dimensions and striking similarity to fungi in Phanerozoic volcanics indicate that they represent fossilized fungus-like mycelial organisms. The observation that fungus-like organisms inhabited submarine basaltic lavas more than 2.4 Gyr ago (Ga) suggests that this habitat was extremely conservative across the Proterozoic and Phanerozoic eons, and raises questions about the antiquity of fungi and the early history of eukaryotes.
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