Land animals proliferate faster than aquatic counterparts

Of the nearly 1.5 million known animal species on Earth, those with backbones come in a stunning array of shapes and sizes. Vertebrates include fish, amphibians, reptiles, birds and mammals, and the number of species within these groups can vary wildly. For example, there are only six species of lungfish and only 25 crocodilians—but roughly 10,000 birds and 9,700 lizards and snakes.

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