Floral diversity, phytogeography, and climatic amelioration during the Early Carboniferous (Dinantian)

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Abstract
Phytogeographic analysis of three Early Carboniferous intervals (Tournaisian–early Visean, Visean, and late Visean–early Namurian A) indicates a high level of phytogeographic differentiation in the beginning of the Early Carboniferous that decreases toward the end of this period. Climatic amelioration (warmer or wetter conditions) in the north middle and high latitudes, caused by the collision of Laurussia and Gondwana at the end of the Early Carboniferous, may be responsible for this decrease in phytogeographic provinciality. Toward the end of the Early Carboniferous, a large number of equatorial genera expand their ranges northward, and the average generic diversity of assemblages in the north high latitudes (Siberia) also rises. Both support the hypothesis of climatic amelioration. Northward migration of equatorial forms and the appearance of new genera endemic to Siberia both contributed to the rise in Siberian diversity. Although this trend is not statistically significant, additional evidence of diversity increase in northern high latitudes tied to climatic amelioration comes from the northernmost limit of diverse (≥ 10 genera) assemblages, which rises from 20°N at the beginning to 55°N at the end of the Early Carboniferous. Global plant diversity assessed at the generic level remained constant during the Early Carboniferous. The increase in Siberian diversity was offset by a decrease in equatorial diversity, perhaps due to the loss of pronounced latitudinal climatic gradients between north-middle and equatorial latitudes.