Micropachycephalosaurus, which has a dome-shaped head, means "little thick-headed lizard." And the best known of them all, Tyrannosaurus rex, was discovered in South Dakota in 1892. The name means tyrant lizard king. Maiasaura, on the other hand, means "good mother." It got its name when the researcher who found it, Jack Horner, found evidence that the dinosaur would chew up plants to feed its newly hatched babies who couldn't leave their nest.