Torosaurus in Canada.
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The Ceratopsids, an iconic group of Dinosaurs which were an important part of the faunas of Late Cretaceous North America and Asia, were large, quapruped herbivores with distinctive neck frills and facial horns over their eyes and noses. One of the largest Ceratopsids was Torosaurus, known from the End Cretaceous of North America, which is thought to have weighed up to 6500 kg, and achieved skull lengths of about 3 m. However, Torosaurus, is similar to Triceratops, another large End Cretaceous Ceratopsid, which has led to an active debate in recent years, as to whether the two genera are in fact the same, and, therefore, whether or not Torosaurus is a valid name at all (in taxonimy, where a group has been named twice, the older name is considered to have priority). This argument derives from the fact that all known specimens of Torosaurus are as large as, or larger than, the largest specimens of Triceratops, while the horns and crest of Torosaurus are essentially a more exagerated variant in the pattern seen in Triceratops, which might imply that Torosaurus fossils represent more mature specimens of Triceratops, rather than a separate species.