The 1.5 tonne mass applies to Chasmosaurus NMC 2280, femur length 762 mm. I'm not aware of a specimen that is much larger. Now Pentaceratops has a femur 880 mm long, and massed 2.5 tonnes. This is about the max size of a white rhino bull (3 tonne values are probably too high). Many ceratopsids were not very large. GSPaul