Statistical description of individual datasets (the twelve genes on the mitochondrial H-strand) and of concatenated datasets (AL). L (bp): length of the gene in base pairs. No cst: number of constant sites in the alignment. No info: number of informative sites in the alignment. AIC: Model selected according to AIC criterion in Modeltest, which always included parameters G (a gamma distribution of substitution rates) and I (a proportion of invariable sites). χ2 (1, 2): chi square test for homogeneity of base frequencies across species on datasets with third codon position removed (P = 1.0 in every case). χ2 (1, 2, 3): chi square test on datasets with codon positions 1, 2 and 3 included.