Ancient warming episodes may help explain flowering plants’ dominance
Two of the warmest intervals of the past 140 million years may have played an important role in reshaping life on land, according to research described by the University of Melbourne. The study examines how major climate shifts coincided with both extinctions and rapid diversification among land plants, including the flowering plants that now dominate many terrestrial ecosystems.
The work, published in Nature Plants, focuses on the mid-Cretaceous and early Cenozoic: periods of exceptional global warmth. Researchers from Australia and Austria argue that these intervals were central to plant evolution, not only for flowering plants but for the other major groups of land plants as well.
That question matters because plants underpin terrestrial ecosystems. They capture energy from sunlight and support the animals, fungi and bacteria that depend on them. Flowering plants in particular are described by the researchers as the most productive and diverse group of land plants, with roughly 400,000 species globally.
A fossil-record problem
Flowering plants began displacing older groups during the middle of the Cretaceous, around 100 million years ago, when dinosaurs were still widespread. Scientists have long considered climate a possible driver of that transition, but demonstrating a clear relationship has been difficult.
A central obstacle is that fossil records are uneven. The number of fossils available differs substantially across periods and regions, meaning that simple species counts can create a distorted picture of diversity through time. A fossil-rich interval can appear more diverse partly because more material survived or has been found.
To address that problem, the team assembled data on more than 60,000 individual fossil occurrences, concentrating on pollen and spores. These microscopic remains can preserve evidence of plant communities across long spans of geological time. The researchers then applied methods intended to reduce the effects of major fossil-record biases and generated revised estimates of plant diversity.
Warm worlds, extinction and expansion
The resulting analysis links the mid-Cretaceous and early Cenozoic warm periods to large-scale changes in plant diversity. The researchers say those climates were associated with both mass extinctions and bursts of diversification.
This is not a simple story of warmth automatically producing more species. Extinction and expansion occurred together across long evolutionary intervals, as changing conditions disrupted existing communities and created opportunities for others. The study instead suggests that climate can be a powerful force in reorganizing the ecological conditions under which plant groups compete, spread and diversify.
For flowering plants, that reorganization may be especially consequential. Their present-day success is tied to extensive relationships with animals, fungi and bacteria. Different species can specialize in pollination, seed dispersal, decomposition and feeding relationships, creating the ecological foundations for very large numbers of species.
Why flowering plants became so influential
The researchers’ account places climate alongside biology and ecology in explaining the ascent of flowering plants. Once flowering plants expanded, their interactions with other organisms could support further specialization. In turn, those relationships helped make them central to most land ecosystems.
They are also major participants in the terrestrial carbon cycle because of their role in taking carbon dioxide from the atmosphere. Understanding how their diversity changed in past warm climates therefore has implications beyond the history of vegetation. It informs how scientists think about the long-term relationship between climate, biodiversity and the systems that support life on land.
The study does not present ancient warm periods as direct analogues for current environmental change. The intervals under examination unfolded over geological timescales and involved ecological conditions unlike those of the modern world. But the fossil record offers evidence that climate shifts can be associated with deep and lasting changes in the makeup of plant life.
Revising the evolutionary timeline
By correcting for uneven sampling in fossil data, the research aims to provide a more reliable view of when diversity rose and fell. That methodological step is important because interpretations of evolutionary history depend on separating biological signals from the accidents of preservation and discovery.
The broader conclusion is that the rise of flowering plants was not isolated from planetary conditions. Periods of extreme warmth appear to have been part of the backdrop to their expansion, while also driving losses and turnover among plant groups. The work offers a climate-centered explanation for a transition that helped shape modern terrestrial ecosystems.
For researchers, the next challenge is to refine how individual regions, plant lineages and ecological interactions responded across these ancient climate shifts. For now, the study adds a large fossil dataset to the case that Earth’s warmest intervals helped set the stage for the botanical world seen today.
This article is based on reporting by Phys.org. Read the original article.
Originally published on phys.org
