Why did the end of the Thulean Land Bridge separate mammal evolution in Europe and North America?

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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 Thulean Land Bridge, formed by the Greenland-Scotland Ridge, served as a vital continental connection that facilitated the exchange of terrestrial mammals between western Eurasia and eastern North America during the early Eocene Epoch.12

In the middle of the Eocene, this land bridge subsided and was severed, effectively cutting off the direct migration route between the two landmasses. By terminating this physical link, the separation prevented the continued intermingling of terrestrial vertebrates across the Atlantic. Consequently, this geographic isolation forced the faunas of Europe and North America to develop along independent evolutionary trajectories, leading to distinct patterns of evolution and speciation in each region.12