Molecular clock analysis of I. ricinus Kunitz peptides. Kunitz nucleotide sequences of I. ricinus groups (G1-G11 and SK) and of ticks and spiders (defined by GenBank accession numbers) were used to infer divergence times within ticks by a Bayesian uncorrelated relaxed lognormal molecular clock model. Four taxon sets were calibrated according to Jeyaprakash and Hoy  and the nodes with the recovered divergence times were labeled: Araneae/Scorpions/Pycnogonida/Acari 459±18 MYA (node S), Argasidae 214±28 MYA (node A), Prostriata 196±27 MYA (node P) and Metastriata 134±22 MYA (node M). The figure shows a maximum clade credibility tree including the mean divergence times (MYA) at each node. Well supported nodes and matching ML and Bayesian analyses (bootstrap values ≥70%, posterior probabilities ≥0.7, see Additional file 4) are indicated with black circles. Nodes with gray circles appeared in the ML and Bayesian trees, but they were not well supported (bootstrap values ≤70% and posterior probabilities ≤0.7). Black squares indicate well supported nodes by the Bayesian analysis (posterior probabilities ≥0.7), but were not resolved in the ML tree. Gray squares indicate well supported Bayesian tree nodes (posterior probabilities ≥0.7) that were less supported in the ML analysis (bootstrap values ≤70%). Non-labeled nodes were not well supported in both analyses (bootstrap values ≤70% and posterior probabilities ≤0.7) and they did not match in both phylogenetic reconstructions. The four best-supported clades (supported well by both analytical methods) are labeled with red circles at the nodes. The red star at the node highlights a clade containing G8 and G11 members at a divergence time of 71 MYA that is similar to the divergence time of G6. The scale bar in MYA is at the bottom center of the tree.