In most books, Triceratops is listed to live between 68-66 MYA (million years ago), however some books list Triceratops as living between 70-66 MYA. The Campanian age ended about 72 MYA and then came the Maastricht. Many articles state that Triceratops is "late Maastricht" dinosaur. All these citations do not give a clear answer: when did Triceratops live? All sources agree that Triceratops lived up to the K-Pg extinction 66 MYA, but when did the earliest Triceratops live?
This may be vague question so put it more empirically: what is the oldest age that a Triceratops fossil is dated to? Not when the first fossil of Triceratops was found but what is the earliest age (in MYA) at which Triceratops are known to have existed? Are there Triceratops fossils from 68 MYA? And from 70 MYA?