Assertion: cetacean's need | /r/CapableOf | breathe air
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Source sentences:
text: Several characteristics point to the ancestral origin of whales including the need to breathe air (unlike fish that have gills) despite living exclusively in the ocean, bones in their flippers which resemble limbs that were once used for walking and hunting on land, and the vertical shape of their spines (more likely designed for running rather than swimming) as opposed the horizontal design and movement of fish.