Torosaurus

Torosaurus (meaning "pierced lizard") was a large, quadrupedal, plant-eating Ceratopsian dinosaur with three horns on its large head. "Torosaurus" hatched from eggs and may have lived in herds.
"Torosaurus" lived during the Upper Cretaceous, about 70–65 million years ago, in what is now western North America. It was similar to "Triceratops". Some had thought that "Triceratops" was a younger form of "Torosaurus".
However, latest thinking is that the two are definitely different genera. In 2011, 2012 and 2013, studies of external features of known specimens decided that shape and development differences mean the two genera are not synonyms. The main problems in the "one genus" idea are: