Tethyan biodiversity hotspots at the community level

Areas of high biodiversity have shifted from the Mediterranean Tethys to the Coral Triangle in the western Pacific throughout the Cenozoic—a phenomenon often linked to plate tectonics shaping habitat heterogeneity. We use assemblage-level data from the Paleobiology Database to document spatiotemporal changes in alpha diversity of marine benthic communities, analyzing over 10,000 collections with at least 30 counted individuals.

Applying both traditional diversity metrics and rank-abundance distribution models, we observe a consistent trend of increasing alpha diversity toward the present and a growing proportion of complex benthic communities over time. Strong correlations between local and regional diversity measures suggest that regional species pools fundamentally structure local community diversity.

Despite potential lithification biases, environmental setting—particularly clastic-influenced reef environments—best explains the preserved spatial distribution of hotspots. Within the Tethys Ocean, biodiversity hotspots consistently occurred away from the equator, primarily along its northwestern margin near the modern Mediterranean, with occasional additional centers in South China, India, and Sinai.

Remarkably, the last time an area corresponding to today’s Indo-Australian Archipelago was a hotspot of local richness was during the Middle Triassic, approximately 245 million years ago. This implies that the modern Coral Triangle is at a truly exceptional place, whereas the western Tethys region served as a stable marine biodiversity hotspot for nearly 200 million years.