Rapid Eocene diversification of spiny plants in subtropical woodlands of central Tibet

Spinescence is an important functional trait possessed by many plant species for physical defence against mammalian herbivores. The development of spinescence must have been closely associated with both biotic and abiotic factors in the geological past, but knowledge of spinescence evolution suffers from a dearth of fossil records, with most studies focusing on spatial patterns and spinescence-herbivore interactions in modern ecosystems. Numerous well-preserved Eocene (similar to 39 Ma) plant fossils exhibiting seven different spine morphologies discovered recently in the central Tibetan Plateau, combined with molecular phylogenetic character reconstruction, point not only to the presence of a diversity of spiny plants in Eocene central Tibet but a rapid diversification of spiny plants in Eurasia around that time. These spiny plants occupied an open woodland landscape, indicated by numerous megafossils and grass phytoliths found in the same deposits, as well as numerical climate and vegetation modelling. Our study shows that regional aridification and expansion of herbivorous mammals may have driven the diversification of functional spinescence in central Tibetan woodlands, similar to 24 million years earlier than similar transformations in Africa.

Automated summary

Spinescence is an important trait for plants to defend against mammalian herbivores. However, the evolution of spinescence remains poorly understood, with most studies focusing on modern ecosystems. Recently discovered well-preserved Eocene plant fossils in the central Tibetan Plateau reveal a diversity of spiny plants and rapid diversification during that time. Regional aridification and expansion of herbivorous mammals may have driven the diversification of spinescence in central Tibetan woodlands.