Some may be taxonomically unique the last representative of an otherwise extinct group of animals, like the duck-billed platypus or the long-beaked echidna while others may differ from each other only slightly.

ECONOMIST: Green.view: Finger on the spot | The

During the times of isolation, a number of species of giant duck-billed dinosaurs "roamed a much smaller area than you might think given that many were larger than elephants, " Gates said.

MSN: Dinosaur boom linked to rise of Rocky Mountains

New species of duck-billed and horned dinosaurs were being born at an explosive rate of every few hundred thousand years during the brief time when the two mountain ranges and the seaway coexisted.

MSN: Dinosaur boom linked to rise of Rocky Mountains

The plea agreement required that he abandon all claims on the T. bataar and the duck-billed dinosaur, and on four more Mongolian and Chinese dinosaurs to which federal prosecutors could now connect him: two oviraptors and two more T. bataars, one of them believed to be somewhere in Great Britain.

NEWYORKER: Bones of Contention