Nedoceratops dinosaurs. Artwork of nedoceratops (formerly known as Diceratops) dinosaurs grazing beneath an oak tree. This horned herbivorous dinosaur is known from fossils discovered in 1868 in Wyoming, USA. It dates from the Late Cretaceous period, 65 to 100 million years ago. This dinosaur was herbivorous, feeding on plants and other vegetation. The ground birds on the right are from the predatory genus Avisaurus. Oak trees emerged about 80 million years ago during the Late Cretaceous period.