Fire-adapted Gondwanan Angiosperm floras evolved in the Cretaceous

Area of Science:

• Paleobotany and Evolutionary Biology
• Plant Ecology and Adaptation

Background:

• Fires have influenced plant evolution for millions of years, with a common belief that fire-prone communities emerged only 15 million years ago.
• Previous studies suggested earlier origins of fire-prone Angiosperm floras in Australia and South Africa around 60 million years ago, but were limited by clade age.
• The role of fire in early Angiosperm evolution remains debated, with a need for deeper phylogenetic insights.

Purpose of the Study:

• To investigate the evolutionary history of fire-adapted traits in the Proteaceae family.
• To determine the timing of fireproneness in Gondwanan Angiosperm floras.
• To understand the co-evolution of seed dispersal and germination mechanisms with fire regimes.

Main Methods:

• Utilized a molecular-dated phylogeny of the Proteaceae family, spanning 113 million years of evolutionary history.
• Analyzed the evolutionary origins of sclerophyllous genera within fire-prone habitats.
• Correlated the timing of evolutionary events with past atmospheric oxygen levels and climate changes.

Main Results:

• Ancestors of key sclerophyll genera (e.g., Protea, Leucadendron) inhabited fire-prone environments as early as 88 million years ago (Mid-Upper Cretaceous).
• This period coincided with peak atmospheric oxygen levels, increasing combustibility.
• Diverse seed storage and fire-cued release/germination mechanisms evolved by 71 million years ago, with ant dispersal emerging later at 45 million years ago.

Conclusions:

• Fireproneness in Gondwanan Angiosperm floras, specifically Proteaceae, can be traced back nearly 90 million years into the Cretaceous.
• On-plant (serotiny) and soil seed storage, along with ant dispersal, represent ancient adaptations to fire in flowering plants.
• The study pushes back the timeline for fire-driven evolution in Angiosperms, highlighting the deep ecological impact of fire.