Epiphytic Overgrowth of Charophyte Thalli by Stromatolite-like Structures and Fungi in the Lower Cretaceous of the Iberian Ranges (Spain)

Abstract

The Lower Cretaceous (113 million years old) lacustrine deposits of Las Hoyas(Iberian Ranges, Cuenca, Spain) yield an epiphytic assemblage formed by thecharophyte species Clavatoraxis diaz-romeraliiMartín-Closas & Diéguez overgrown by a muddy, laminatedstromatolite-like structure. Fossil charophyte thalli coated with biogeniclaminations were previously unknown from the fossil record. Within thisstromatolite-like structure, filaments are found which correspond to thalli ofanother charophyte, Palaeonitella vermicularisMartín-Closas & Diéguez, and to septate hyphae of fungi(Ascomycetes). The distribution pattern of the biogenic lamination and itsselective growth only on the strongest thalli ofClavatoraxis diaz-romeralii suggests that it occurredwhen these macrophytes were still alive, standing upright on the lake bottom.From this point of view the stromatolite-like structures are reminiscent ofextant overgrowths of charophyte thalli by epiphytic, filamentouscyanobacteria, eucaryotic algae and fungi. These assemblages appear to developafter eutrophication of nutrient-poor environments, which are more suitablefor charophyte growth.