Previous molecular systematic studies of "true" Phocid seals based in single loci have been unable to resolve relationships among Harbour, Ringed, and Grey Seals (Phoca, Pusa, & Halichoerus), or among Hooded, Harp, and Spotted seals (Cystophora, Pagophilus, & Histriophoca). Analysis of complete mitochondrial genome sequences resolves three of four branch points in 100% of bootstrap replicates. The phylogeny suggested by these data will require reconsideration of nomenclature, and previous evolutionary interpretations of behavioural, biogeographic, and cytogenetic evolution.
The study demonstrates the behaviour of statistical (bootstrap) support with increasing amounts of sequence data. At least 4000bp are necessary to obtain >95% confidence on the deeper branches. On the most recent branch, Pusa and Halichoerus are joined as sister species with bootstrap confidences of 48%, 60%, 67%, 78%, & 81% with resampling of 1, 2, 4, 8, & 13 kbp, respectively.