Invertebrate commonality trends at the generic level between landmasses on the eastern and western sides of the present North Atlantic, as computed from data in the Treatise on Invertebrate Paleontology, have an intriguing relationship with plate tectonic events. Commonality peaks in early Paleozoic time coincided roughly with Taconic and Caledonian orogenic events. Following an Early and Middle Devonian decrease, an increase in commonality through the late Paleozoic apparently reflects plate tectonic processes associated with the Acadian, Alleghenian, and Hercynian orogenies. Commonality highs can be attributed to proximity of land masses, building of island arcs, and transfer of crustal blocks during continental convergence and divergence. The commonality data support the hypothesis of a proto–Atlantic Ocean during early Paleozoic time.
An all-time commonality high was reached in Triassic time, associated with Pangean continental assembly, and commonality has decreased since then, reflecting continental fragmentation and divergence.