Two models for the evolution of ice-breeding behaviour in phocid seals

    According to the traditional classification based on morphology (left), Phocid ("True") seals were originally land-breeding (red lines): pagophilic (ice-breeding) behaviour evolved in parallel three times, in response to separate adaptive pressures.

    A molecular systematic classification (right) shows instead that pagophilic breeding is ancestral: a shift to terrestrial breeding has occurred only once. The molecular-based model is more parsimonious. Harp Seals, often considered more closely related (as Phoca groenlandica) to Harbour (Phoca vitulina), are in fact more closely related (as Pagophilus groenlandicus) to Hooded Seals (Cystophora). Grey Seals (Halichoerus), despite their distinctive morphology, are the sister species to Ringed Seals (Pusa) (after Perry et al. 1995; Carr & Perry 1997)


Figures & text material © 2019 by Steven M. Carr