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Description
Size comparison of large aquatic animals that lived between 65 million years ago and 4 million years ago.
Upper row: Rytiodus capgrandi (large, tusked dugong), Acrophoca longirostris (ancestor of leopard seal), Livyatan melvillei (primitive sperm whale with gigantic teeth), Pelagiarctos thomasi (predatory walrus with hyena-like teeth), Paleoparadoxia tabatai (hippo-like marine herbivore related to elephants and manatees) and Janjucetus hunderi (predatory whale ancestral to modern baleen whales).
Middle row: Mammalodon colliveri (bottom-feeding whale ancestral to modern baleen whales), Aivukus (giant walrus), Psephophorus polygonus (large sea turtle related to modern leatherback turtle), Megalampris keyesi (huge opah), Acrophyseter deinodon (early sperm whale), Heliobatis radians (fresh-water ray), Otodus obliquus (huge mackerel shark) and Gomphotaria pugnax (four-tusked walrus).
Lower row: Campanile giganteum (the largest sea snail ever), Megapiranha paranensis (large piranha), Allodesmus kelloggi (primitive seal) and Parabalaeonoptera baulinensis (large, early baleen whale).

Description
Size comparison of large aquatic animals that lived between 65 million years ago and 4 million years ago.
Upper row: Rytiodus capgrandi (large, tusked dugong), Acrophoca longirostris (ancestor of leopard seal), Livyatan melvillei (primitive sperm whale with gigantic teeth), Pelagiarctos thomasi (predatory walrus with hyena-like teeth), Paleoparadoxia tabatai (hippo-like marine herbivore related to elephants and manatees) and Janjucetus hunderi (predatory whale ancestral to modern baleen whales).
Middle row: Mammalodon colliveri (bottom-feeding whale ancestral to modern baleen whales), Aivukus (giant walrus), Psephophorus polygonus (large sea turtle related to modern leatherback turtle), Megalampris keyesi (huge opah), Acrophyseter deinodon (early sperm whale), Heliobatis radians (fresh-water ray), Otodus obliquus (huge mackerel shark) and Gomphotaria pugnax (four-tusked walrus).
Lower row: Campanile giganteum (the largest sea snail ever), Megapiranha paranensis (large piranha), Allodesmus kelloggi (primitive seal) and Parabalaeonoptera baulinensis (large, early baleen whale).