The enigmatic biotic and environmental changes during the Carnian Humid Episode (CHE) have been investigated in South China. The body size of conodonts, assessed as length of P1 elements, and their diversity show substantial changes in the mid-Carnian. The well-dated Long Chang, Yongyue and Caizitang sections in southwestern China record a change of palaeoenvironments from shallow-marine carbonate platforms to deeper, euxinic basins. All sections show a major loss of conodont diversity and abundance late in the Julian 1 at a time of rapid warming and marine anoxia. Conodont size saw a reduction in maximum, mean and minimum size during the Julian 2 to Tuvalian 2 interval caused by the short-lived appearance of small species and a size decrease of the survivors. Conodont mean size reduction coincided with marine euxinia or anoxia and temperature fluctuations during the Julian 2 to Tuvalian 2 interval. Carnian conodonts thus follow Bergmann's Rule: element size is inversely correlated to the temperature. Climate warming with the consequential development of marine anoxia or euxinia is probably directly responsible for biotic changes at this time.

Supplementary material: Conodont length data from the Long Chang (LC), Yongyue (NR) and Caizitang (CZ) sections and data for the cross plot between estimated temperature and conodont mean size in the Long Chang section are available at https://doi.org/10.6084/m9.figshare.c.4114424

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