Rather than laying eggs, mammals give birth to live young. The primary distinction is thermoregulation; mammals are warm-blooded, maintaining a constant internal temperature regardless of the freezing or boiling temperatures of the water around them.
How Marine Mammals Breathe Air Using Lungs
Unlike fish, which extract oxygen directly through their gills, these animals possess lungs and must consciously breathe. Their closest living relatives are actually elephants.
Diverse Lineages: From Shallow Rivers to Open Ocean The term "aquatic mammal" encompasses a wide array of species that have taken to the water from different ancestral lines. Whales and Dolphins (Cetaceans): The most iconic of the group, these creatures evolved from land-dwelling artiodactyls (even-toed ungulates).
How Marine Mammals Breathe Air Using Lungs
Despite their varied origins, they all share the core mammalian traits that link them to humans, cows, and bats rather than to the fish they mimic. They use rocks to crack open shells and rely on their incredibly dense fur—up to one million hairs per square inch—to trap air for insulation.
More About What aquatic animals are mammals
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