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How did the closure of the Tethys seaway affect marine organisms?

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Messinian Stage — Tertiary Period Gypsum cones, which resulted from the evaporation of the Mediterranean Sea during the Messinian Salinity Crisis, in the Sorbas basin, Spain.

The closure of the Tethys seaway, which occurred progressively as continental fragments collided with Eurasia, significantly impacted marine life. The final severance of the seaway in the late Early Miocene, approximately 15 million years ago, led to the disappearance of many larger tropical foraminiferans known as nummulitids.12

Prior to this closure, these lens-shaped organisms occupied a vast habitat stretching from Indonesia to Spain and as far north as Paris and London. While descendants of these nummulitids persist in the Indo-Pacific region today, they exhibit significantly reduced diversity compared to their predecessors.2

Beyond this specific extinction event, the collision of India and southern Asia—which initiated the blocking of the Tethys—also altered global oceanic productivity by increasing erosion and nutrient runoff into the Indian Ocean, further influencing marine environments during the Tertiary Period.1