Reply to the Comment on “Quantitative biochronology of the Permian–Triassic boundary in South China based on conodont unitary associations”

Abstract

1. Introduction In their Comment, Jiang et al. (2016) claim that the discordance between our zonation (Brosse et al., 2016) and the interval zones does not rest on the use of the Unitary Association method (Guex, 1991 and Guex et al., 2015) per se but on our “failure to use the most recent published conodont ranges from some key Chinese sections”. They add that our analysis is based on “unreliable taxonomic data sets with unjustified taxonomic re-assessments”, and hence, that we did not demonstrate that the Unitary Association method performs better than traditional interval zones. Additionally, the Comment by Jiang et al. (2016) contains misunderstandings pertaining to the method used in our study (Brosse et al., 2016). Our goal was to apply the Unitary Association Method on a dataset of conodont distributions from South China around the Permian–Triassic boundary (PTB) in order to reassess the quality of the corresponding data and to provide a discrete and robust alternative zonation to the continuous, First-Occurrence-based interval zones. Such interval zones are routinely utilized in Permian and Triassic conodont biostratigraphy, regardless of their abundant internal contradictions. Three categories of points of contention can be extracted from the Comment of Jiang et al. (2016): method, selection of data and taxonomy, and illustrations. Each of these is addressed separately below. 2. Method Fig. 1 complies with the recommendation of Jiang et al. (2016) and takes into account all the recent literature, summarizing the most recent published conodont ranges from the relevant sections. The reader will immediately observe that the sequences of First Occurrences (FOs) used in the most recently published interval zones occupy contradictory positions between the different sections. This is precisely the main criticism expressed in our work. This problem cannot be solved by simply standardizing the taxonomy of the considered taxa. Many contradictions do persist after taxonomic homogenization. As conceded by Jiang et al. (2016), FOs are prone to diachronism. But contrary to what Jiang et al. (2016) suggest, sampling effort is not the only nor the main reason for such diachronism and PTB sections from South China are no exceptions in this respect. Fig. 9 of Brosse et al. (2016) demonstrates the contrary. Ironically enough, Jiang et al. (2016) acknowledge that Last Occurrences (LOs) can be diachronous because of local, ecological differences, but they exclude that FOs can be affected. In reality, these authors unduly equate every local FO with an alleged instantaneous spreading of a species across all sections. Incidentally, such an unwarranted assumption also deliberately ignores that speciation is an intrinsically space-restricted evolutionary process.