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Why do sea turtles have streamlined shells?

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Illustrations of ten representative chelonians, including spiny softshell turtle, Galapagos giant tortoise, green turtle, alligator snapping turtle, Blanding's turtle, common map turtle, eastern box turtle, eastern painted turtle, spotted turtle, and eastern mud turtle, each labeled with its common and scientific name. A scale bar at the bottom shows size comparison. — turtle Turtles (order Testudines).

Sea turtles have streamlined shells as an adaptation to facilitate efficient movement through their aquatic environments. Because these reptiles are highly aquatic, a streamlined shape reduces drag, allowing them to propel their bodies through the water more effectively using their flippers.12

This physical trait is a key distinction between sea turtles and other aquatic turtles, such as snapping turtles or the matamata, which are bottom-walkers and possess less streamlined, often ridged shells that may assist in camouflage.1