Visitors to Chicago’s Field Museum are familiar with “Sue” the famous Tyrannosaurus Rex skeleton that is on display.

Now visitors will see a much smaller and rarer set of dinosaur bones. Archaeopteryx (ar-key-aap-tricks) is a bird that lived 150 million years ago and is a link between dinosaurs and birds. Jingmai (Jing-May) O’Conner, the Fields’ Dino Curator says the fossil is one of the best species of what she calls a ‘holy grail’ find.

The fossil is just one of 13, it’s regarded as perhaps the best one ever found and the only one on display in a North American museum.