Classification and evolution - What are the two principles used to classify species?
Different groups of animals can be distinguished by their distinctive gaits.
Lizards have a sprawling gait: their limbs are spread out and low to the ground.
Crocodiles have a semi-erect gait: their limbs are angled and their body is slightly higher off the ground.
Birds have a fully upright gait. Their limbs point straight down and they walk rather than crawl along the ground.
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