Which was the youngest dinosaur?

The most recent dinosaurs are found in rocks that date from just before the extinction layer 66 million years ago. Again there is no single youngest dinosaur, because dinosaurs tend to be found in 'communities' of animals rather than just isolated animals. These communities include dinosaurs such as the ceratopian Triceratops, the hadrosaur Anatotitan and the tyrannosaur Tyrannosaurus. These were among the most recent of all dinosaurs.