The Pangea B–pangea a Transition in the Permian: Implications for Biodiversity Evolution

There are two possible reconstructions of Pangea for Pennsylvanian to Lopingian times: these are the Pangea A and Pangea B configurations and they have been debated for over 40 years. They mainly differ by the juxtaposition of Gondwana and Laurasia at this time. In Pangea A configuration, NW Africa is adjacent to Laurentia, essentially the same as the so-called “Bullard fit” at the onset of Triassic rifting in the Central Atlantic, whereas in Pangaea B configuration, the north Andean margin of South America is adjacent to Laurentia. They also differ in timing, as they transition from one to the other during the Guadalupian: the Pennsylvanian-Cisuralian Pangea B transitioning to the Lopingian Pangea A (Bullard fit) through a large-scale (~3500 km) dextral shear. This profound reconfiguration has led to a reorganization of geographic and climatic patterns and has deeply affected shallow-marine habitat distribution during the Permian, thereby driving biodiversity evolution. A recent compilation of regional and global brachiopod occurrences and ranges has shown a peak in biodiversity in the Guadalupian, which may be related to the tectonic reorganization that accompanied the transition from Pangea B to Pangea A. This transition, the opening of the Neo-Tethys Ocean and the rifting and drifting of peri-Gondwanan terranes generated shallow-marine habitat availability and a connected tropical realm by shallow shelves, seaways, and marine corridors. Plate reorganization associated with the Pangea B–to–A transition may thus have been the primary driver of benthic invertebrate biodiversity evolution in the Guadalupian-Lopingian, rather than climate change associated with the demise of the LPIA.