RT Journal Article SR Electronic T1 Rewinding the molecular clock in the genus Carabus (Coleoptera: Carabidae): Revisiting Andujar et al. in light of new fossil evidence and the Gondwana split JF bioRxiv FD Cold Spring Harbor Laboratory SP 2020.02.19.912543 DO 10.1101/2020.02.19.912543 A1 Lars Opgenoorth A1 Sylvia Hofmann A1 Joachim Schmidt YR 2020 UL http://biorxiv.org/content/early/2020/02/20/2020.02.19.912543.abstract AB Background Molecular clocks have become powerful tools given increasing sequencing and fossil resources. However, outcome of calibration analyses depend on choosing priors. Here we revisit a seminal dating study of the genus Carabus by Andujar et al. proposing that their prior choices need re-evaluation with the hypothesis that reflecting fossil evidence and the Gondwanan split properly rewinds the molecular clock significantly. We used the similar dataset including five mitochondrial and four nuclear DNA fragments with 7888 nt total length. We set the root age based on the fossil evidence of Harpalinae ground beetles in the Upper Cretaceous and introduce the Paleogene divergence of the outgroup taxa Ceroglossus (endemic to South-America) and Pamborus + Maoripamborus (Australia, New Zealand) as a new prior based on current paleontological and geological literature.Results The ultrametric time-calibrated tree of the extended nd5 dataset resulted in a median TMRCA Carabus age of 59.72 Ma (HPD95% 49.92-70.38), roughly 35 Ma older than in the Andujar study. The splits between C. rugosus and C. morbillosus (A), between C. riffensis from the European Mesocarabus (B), and between Eurycarabus and Nesaeocarabus (C) were dated to 19.19 (13.16-25.64), 25.95 (18.68-33.97), and 23.99 (17.75-31.67) Ma and were thus decidedly older than previously reported (7.48, 10.93, and 9.51 Ma). Constraining the Carabidae time tree root with the Burmese Oodini amber fossil at ∼99 Ma resulted in the largest increase, while including the Canary Hotspot and Gondwana split calibrations stabilized the overall dating, mediating between the root and remaining calibration points. Utilizing our clades A-C results, TMRCA of Carabus was dated to 53.56 (41.25-67.05) Ma in the complete MIT-NUC data set compared to 25.16 (18.41-33.04).Conclusion Taking into account the Gondwanan split as a new prior, together with the fossil evidence of the outgroup taxon Harpalini in the Late Cretaceous, our new approach supports an origin of the genus Carabus in the Paleocene-Early Eocene. Our results are preliminary due to the heavy reliance on the nd5 gene and thus will have to be tested with sufficient set of nuclear markers. Such subsequent analyses will likely extend the dating even further back in time.