Carboniferous brachiopod migration and latitudinal diversity: a new palaeoclimatic method

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Abstract
Patterns of migration of organisms, coupled with changes in latitudinal diversity, provide useful information for reconstructing palaeoclimate. We apply these tools to the record of 344 articulate brachiopod genera from the Tournaisian, Visean, and Namurian stages of the Carboniferous. Localities from the Northern Hemisphere were assigned to four palaeolatitudinal zones: the palaeoequatorial zone and the low, middle and high latitudes. Generic migrations were tabulated among latitudinal zones for each pair of successive stratigraphic intervals. Latitudinal diversity gradients were calculated based on the number of genera present within each zone. Two intervals of climatic change were identified by these methods. Between the middle and late Visean, 42% of the genera moved the northern boundary of their range northward, and nonequatorial diversity rose dramatically. These patterns indicate high-latitude warming, which may have been caused by deflection of the circumequatorial current as the collision of Laurussia and Gondwana progressed. Migration and latitudinal diversity patterns indicate both high-latitude cooling and equatorial warming between the Namurian A and B. The onset of Gondwanan glaciation may have been responsible; similar patterns occurred during glacial onset in the Miocene.