Format: ORAL

Candela Blanco-Moreno1,2, Virginia Valcrcel1,3, Nagore G. Medina1,3

1 Departamento de Biología, Universidad Autónoma de Madrid, Madrid 28049, Spain. 2 Biological Sciences Department, California State Polytechnic University, Humboldt, Arcata, CA USA 3 Centro de Investigación en Biodiversidad y Cambio Global (CIBC-UAM), Universidad Autónoma de Madrid, Madrid 28049, Spain

A comprehensive understanding of the ecological niches occupied by the ancestors of todays plant clades is essential for elucidating the evolutionary pathways that have shaped contemporary diversity. Integrating present-day observations with fossil records is crucial for studying these niches accurately. However, incorporating fossil information into phylogenetic ancestral reconstructions is challenging due to the limited direct information on the ecological niches of fossilized plants. Our work reviews the primary uses of fossils in niche reconstructions and identifies significant gaps in fossil knowledge. Deep time reconstructions often rely on morphological analyses of fossils due to difficulties in obtaining niche information from ancient specimens. Traits of extant plants like stomata, growth rings, tracheid size and thickening types, or foliar architecture (e.g. CLAMP) have proven to be indicative of present climatic conditions and in some cases are utilized for paleoclimatic reconstructions. However, the use of plant traits is based on inferences made on certain groups of extant plants and loses its applicability in deeper time as the taxonomic and atmospheric differences become so great that the comparison is unreliable (e.g. studies stomatal density in Carboniferous Pteridosperm leaves do not show consistent results). Additionally, the use of traits of the plant taxa themselves could lead to circular reasoning. Alternative methods, such as isotopic analyses and sedimentology, offer additional evidence on the abiotic conditions in which the plant fossilized evidence but face limitations in data scarcity. Our review examines plant traits, sedimentology, and stable isotope data from 15 fossil taxa (spanning from 470 to 100 Ma) that are commonly used to calibrate the land plant tree. This forms the basis for developing a methodological framework to infer the ancestral niches of the main clades of extant land plants, ensuring consistency and comparability in future research.