1. Marine reptiles were air-breathing creatures that lived in the water. Like today's turtles and crocodiles, they would hold their breath while under water.
2. Marine reptiles are grouped in the following categories: ichthyosaurs, tuna- or dolphinlike in appearance, but unrelated to them; placodonts, small to medium-sized, bottom-feeding reptiles that resembled armor-plated walruses; nothosaurs, streamlined, swift, seal-like predators; plesiosaurs, large long-and short-necked open-ocean predators; marine crocodiles, several kinds of ocean-going crocodiles; mosasaurs, swift predators with short necks and powerful jaws; and marine turtles, the first true seagoing turtles.
3. Marine reptiles adapted to ocean life by optimizing anatomical traits that reduced drag and provided them with speed and maneuverability in the water.
4. Features such as webbed or flipperlike limbs and a vertical flattening of the tail aided in locomotion and could have also helped them to dive deep.
5. The ichthyosaur Shonisaurus is now the largest of all known marine reptiles, measuring about 77 feet (23 m) long.
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