Two periods of extreme greenhouse warmth triggered the biggest shifts in land-plant diversity over the past 120 million years, according to a study published in Nature Plants. The research shows that floristic turnover—encompassing both the appearance of new plant types and the disappearance of older ones—was concentrated within brief mid-Cretaceous and early Cenozoic episodes of extreme global warmth, synchronized across high and low latitudes.
Flowering plants, or angiosperms, became ecologically dominant across most terrestrial biomes over this timeframe, displacing other groups of land plants. While this transition was delayed until the early Cenozoic tens of millions of years after major angiosperm groups first emerged, the new findings indicate that extreme warmth served as a primary driver. The study was authored by J.M.K. Sniderman, G.J. Jordan, and C. Mays, according to Floraldaily.
Overcoming Fossil Record Biases
Historically, establishing a clear link between climate and plant diversity proved challenging because fossil records are heavily biased. The availability of fossils varies significantly across different regions and geological time periods, meaning that a simple count of fossilised species in a given location can present a misleading picture of evolutionary diversity.
To address this distortion, the researchers compiled a dataset of over 60,000 fossil pollen and spore records covering approximately 130 million years. They incorporated records sourced from high-latitude southeastern Australia as well as tropical regions in northeastern Africa and northern South America. By applying multiple statistical methods designed to standardize sampling, the team ensured that time periods possessing a greater number of individual fossils did not disproportionately dominate the results.
Impact Across Multiple Plant Groups
The analysis revealed that the climate-driven turnover pattern extended well beyond flowering plants alone. Conifers and their relatives, along with mosses and ferns, also experienced significant booms and responses during these hotter intervals at both high and low latitudes.
Rather than simply fostering straightforward biodiversity growth, the ancient greenhouse intervals proved highly disruptive. The extreme warmth eliminated much of the previously established plant diversity that had dominated land ecosystems while simultaneously generating conditions that fostered the evolution of new plant forms. Each of these ancient intervals lasted for a few million years.
The researchers also evaluated alternative factors that could explain the observed shifts, such as geographic isolation—exemplified by Australia drifting away from the southern supercontinent Gondwana—and biological interactions among various plant groups. While those factors played roles, the global climate pattern provided a more complete explanation for the broad turnover signals.
Implications for Modern Climate Change
The study cautions against using ancient plant diversification as reassurance for contemporary environmental changes. Human-driven global warming occurs at a much faster pace than the greenhouse phases identified in the fossil record, meaning modern warming is likely to cause major plant extinctions much more rapidly.
While extinct ancient species were eventually replaced by new flora, that evolutionary process required millions of years. Consequently, current losses cannot be offset by the prospect that new species might eventually evolve, making habitat preservation and the reduction of carbon dioxide emissions essential for keeping existing ecosystems intact, as reported by karmactive.com.