Why are there no animals with three legs?

If "Why?" is the first question in science, "Why not?" must be a close second. Sometimes it's worth thinking about why something does not exist.

New fossil shows Archaeopteryx sported 'feathered trousers'

The origin of feathers and the origin of flight have been a contentious chicken-and-egg issue in the scientific world for decades. Did feathers develop as a flight mechanism - or were they first used for other purposes?

Mate choices of barn swallows tied to diverging appearances

If you are a male barn swallow in the United States or the Mediterranean with dark red breast feathers, you're apt to wow potential mates. But if you have long outer tail feathers in the United States, or short ones in the ...

Peacocks shake feathers to mesmerize mates

Call it a shimmy meant to hypnotize. When courting a female, peacocks fan their colorful rear feathers and shake them, but somehow keep their plumes' iridescent circles, or eyespots, nearly still, like a fixed stare.

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