Reply detection of a 27.5-My cycle in extinctions of non-marine tetrapods in light of a similar cycle in marine extinctions and coordinated geologic events

Abstract

ABSTRACT Our circular-spectral and Fourier analyses of the ages of the 10 recognized non-marine tetrapod extinction events over the last 300 My revealed a significant spectral peak at 27.5 My. Omerbashich, using his Gauss-Vaniçek method of spectral analysis, fails to find a significant 27.5 My cycle in the same data. He claims to find predominant short (< 1 My) Earth precession cycles in the data set, where the smallest interval between extinction events is 8 My. In response to Omerbashich, we performed a new analysis of non-marine extinctions using a best-fit method that again displays the high spectral peak at ~27.5 My. A similar cycle has been widely reported in the related record of the ages of extinction events of marine species, although earlier Omerbashich (2006), using the same Gauss-Vaniçek method, was not able to detect that cycle. Furthermore, using a new compilation of the ages of 89 major geologic events over the last 260 My (including the extinction events), we also find evidence for the 27.5 My cycle pervading the geologic record. We conclude, therefore, that the evidence suggests that the 27.5 My cycle that we detected is physically meaningful. In our paper (Rampino et al., 2020) we reported evidence, using circular-spectral and Fourier-analysis methods, for a significant underlying 27.5 My periodicity in the ten episodes of extinctions of non-marine tetrapod families over the last 300 My. We compiled the extinction data from an exhaustive search of the relevant geological literature on non-marine tetrapod occurrences, and we believe that we have detected the major non-marine extinction events. Four of the ten non-marine events lacked published estimated magnitude data, but we suggested, based on the magnitudes of the other distinct extinction events, that they most likely represented ≥ 10% extinction of tetrapod families (Rampino et al., 2020). It is important to note, however, that we did not make use of the percent-extinction estimates in any of our statistical analyses; we treated the ages as Dirac delta functions (spikes), so that, counter to the methods of Omerbashich (2021), the relative amplitudes are irrelevant in our study.