Comparative biogeography: innovations and the rise to dominance of the North Pacific biota

The North Pacific is the largest cold-water source of lineages spreading to other modern marine temperate biotas. How this status was achieved remains unclear. One hypothesis is that functional innovations of large effect, defined as departures from the norm in temperate clades and which confer competitive or defensive benefits, increase resource availability, and raise performance standards in the biota as a whole, evolved earlier and more frequently in the North Pacific than elsewhere in the temperate zone. In support of this hypothesis, phylogenetic and fossil evidence reveals 47 temperate marine innovations beginning in the latest Eocene, of which half arose in the North Pacific. Of the 22 innovations of large effect, 13 (39%) evolved in the North Pacific, including basal growth in kelps and bottom-feeding herbivory and durophagy in mammals. Temperate innovations in the Southern Hemisphere and the North Atlantic appeared later and were less consequential. Most other innovations arose in refuges where the risks of predation and competition are low. Among temperate marine biotas, the North Pacific has the highest incidence of unique innovations and the earliest origins of major breakthroughs, five of which spread elsewhere.

Clawed forelimbs allow northern seals to eat like their ancient ancestors

Streamlined flippers are often considered the defining feature of seals and sea lions, whose very name 'pinniped' comes from the Latin pinna and pedis, meaning 'fin-footed'. Yet not all pinniped limbs are alike. Whereas otariids (fur seals and sea lions) possess stiff streamlined forelimb flippers, phocine seals (northern true seals) have retained a webbed yet mobile paw bearing sharp claws. Here, we show that captive and wild phocines routinely use these claws to secure prey during processing, enabling seals to tear large fish by stretching them between their teeth and forelimbs. 'Hold and tear' processing relies on the primitive forelimb anatomy displayed by phocines, which is also found in the early fossil pinniped Enaliarctos. Phocine forelimb anatomy and behaviour therefore provide a glimpse into how the earliest seals likely fed, and indicate what behaviours may have assisted pinnipeds along their journey from terrestrial to aquatic feeding.

Comparative feeding strategies and kinematics in phocid seals: suction without specialized skull morphology

Feeding kinematic studies inform our understanding of behavioral diversity and provide a framework for studying the flexibility and constraints of different prey acquisition strategies. However, little is known about the feeding behaviors used by many marine mammals. We characterized the feeding behaviors and associated kinematics of captive bearded (Erignathus barbatus), harbor (Phoca vitulina), ringed (Pusa hispida), and spotted (Phoca largha) seals through controlled feeding trials. All species primarily used a suction feeding strategy but were also observed using a biting strategy, specifically pierce feeding. Suction feeding was distinct from pierce feeding and was characterized by significantly faster feeding times, smaller gape and gape angles, smaller gular depressions, and fewer jaw motions. Most species showed higher variability in suction feeding performance than pierce feeding, indicating that suction feeding is a behaviorally flexible strategy. Bearded seals were the only species for which there was strong correspondence between skull and dental morphology and feeding strategy, providing further support for their classification as suction feeding specialists. Harbor, ringed, and spotted seals have been classified as pierce feeders based on skull and dental morphologies. Our behavioral and kinematic analyses show that suction feeding is also an important feeding strategy for these species, indicating that skull morphology alone does not capture the true diversity of feeding behaviors used by pinnipeds. The ability of all four species to use more than one feeding strategy is likely advantageous for foraging in spatially and temporally dynamic marine ecosystems that favor opportunistic predators.