Shifting landscapes shaped Madagascar's unique biodiversity
by Robert Schreiber
Berlin, Germany (SPX) Oct 27, 2025
A team of researchers at ETH Zurich has discovered that Madagascar's dramatic topography and exceptional biodiversity can be traced to a pair of ancient rifting events separated by nearly 80 million years. The first tectonic shift, around 170 million years ago, detached Madagascar from Africa, generating a rugged western escarpment and a tilted plateau. Rivers initially drained eastward across this landscape.

Around 90 million years ago, a second rifting episode divided Madagascar from India and the Seychelles. This event caused the island to tilt westward, resulting in reversed river courses, a new eastern escarpment along the Indian Ocean, and a major shift in Madagascar's water divide.

Lead author Romano Clementucci stated, "The key to understanding Madagascar's landscape lies in its water divide. When the island tilted after each rifting event, the main water divide, the line separating rivers flowing east or west, jumped across the island, transforming its hydrology and erosion patterns." The investigators found that river drainage and erosion patterns were dramatically reorganized. Old rivers reversed or rerouted, and new landforms emerged, with the western region evolving into worn highlands and plateaus, while the east became defined by its steep, linear escarpments.

Madagascar is recognized as one of the world's greatest biodiversity hotspots, with more than 90 percent of its mammals and reptiles, and over 80 percent of its plants endemic to the island. Previous explanations focused on climate and continental isolation, but recent studies introduce geological mechanisms, such as landscape-driven speciation. Clementucci added, "Our work adds a new piece to the puzzle. We show how ancient tectonic forces reshaped Madagascar's surface, tilting the island and shifting the main rivers and mountain divides. Over millions of years, this created fragmented environments where species evolved independently, especially along the island's dramatic eastern escarpment."

The research indicates that regions thought to be geologically stable, such as Madagascar, South Africa, India, Brazil, Australia, and other passive margins, continue to undergo dynamic changes that shape biodiversity. The findings offer fresh insight into how landscape evolution can act as a driver of speciation, complementing established climate-based theories.

Research Report:Madagascar's landscape evolution: A tale of two rifts

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