Marine mammals are fascinating beasts. Whales, manatees, seals, otters...they've all gone back to the water and in the process evolved all kinds of spectacular adaptations to make a living in a soggy setting. Toothed evolved an ability to “see” the underwater world around them using echolocation - basically sonar - to track prey with high-pitched sounds and echoes. A 23 million years old fossil from South Carolina called Cotylocara shows toothed whales could echolocate early in their evolutionary history. A more surprising adaptation to life in the water was preserved with another new whale fossil from California. Called Semirostrum, the new whale has a huge underbite and long chin which was probably used as a sensitive probe to track down buried prey. Whales in the water are interesting, but not unexpected. Our final study examines how SLOTHS adapted to life in the ocean. Thalassocnus was a relative of giant ground sloths, a solidly terrestrial group of animals. A recent study showed how Thalassocnus gradually acquired thickened bones, a trait that has been observed in nearly every mammal that has gone back to the water. Even if it’s a weird animal to imagine clawing through the water, it adapted to that lifestyle in exactly the way paleontologists expect any mammal to get back to the water!
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