[MUSIC] Joan Cartan-Hansen,Host: Dinosaurs can be split into two groups based on their hips.
Saurischians or lizard-hipped dinosaurs have a pair of hip bones that pointed forward or down.
They include meat-eating theropods like Allosaurus and some plant-eaters like Diplodocus.
Ornithischians or bird-hipped dinosaurs had two pairs of hip bones pointing backwards.
They were all plant eaters.
Scientists think birds evolved from lizard-hipped dinosaurs rather than bird-hipped dinosaurs.
But new research thinks there may be other ties.
Sometimes, new discoveries test old ideas.
In 1854, a life-sized sculpture of an iguanodon went on display.
The dinosaur had a horn on the tip of its nose.
Scientists now think the horn was actually a misplaced thumb bone.
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