Could Triceratops skull reach 3m long or more ? and thanx !!

One complication attached to this question is that Scannella and Horner (2010) argued that ceratopsian specimens assigned to Torosaurus, which is normally considered a slightly larger close relative of Triceratops, actually represent very mature Triceratops individuals. This might be correct, but would require significant and rapid changes in the structure of the skull as the animal reached full maturity, so some palaeontologists (including me) are sceptical of the idea.

Scannella and Horner stated that the largest skulls traditionally identified as Torosaurus "approach three meters in length", implying that they do not actually reach or exceed 3 m. They also referred to a skull that is "extremely large" among those traditionally identified as Triceratops, with an estimated length (the length could not be measured precisely because the skull is damaged) of 2.5 m.

The largest Triceratops skulls, then, probably measure about 2.5 m, but might be closer to 3 m if Scannella and Horner are correct that the specimens that have been called Torosaurus really belong to Triceratops. It seems unlikely that they quite reached 3 m in either case, however.

Reference:

Scannella, J. B. and Horner, J. R. 2010. Torosaurus Marsh, 1891, is Triceratops Marsh, 1889 (Ceratopsidae: Chasmosaurinae): synonymy through ontogeny. Journal of Vertebrate Paleontology 30: 1157-1168.