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)
