I saw a video of a young sea turtle sleeping under water. How is that possible? They have to breathe above the water.

I looked it up. It's amazing what other creatures can do and what we can't do.

"As sea turtles are air-breathing reptiles, they need to surface to breathe. Sea turtles can hold their breath for several hours, depending upon the level of activity. A resting or sleeping turtle can remain underwater for 4-7 hours."

Natural Selection makes this stuff possible.