Torosaurus

Phylogeny: Dinosauria > Ornithischia > Genasauria > Neornithischia > Cerapoda > Marginocephalia > Ceratopsia > Neoceratopsia > Coronosauria > Ceratopsoidea > Ceratopsidae > Chasmosaurinae > Triceratopsini

Overview: Torosaurus was one of the largest known members of the family Ceratopsidae, as well as one of the last to appear in the fossil record. It lived close to the very end of the Cretaceous, in what is now the western United States and Canada, where its fossils can be found in the rocks of the Lance, Hell Creek, Scollard and other geological formations. Adults were about eight or nine meters in length, with quite robust and heavy builds overall. The creature’s skull alone was huge, being a contender of the largest of any land-dwelling animal in earth’s history, measuring close to three meters long on some individuals. Ceratopsids all had bony frills growing from the back of the skull, which in the case of Torosaurus was particularly exaggerated. It was long, often rectangular in form and sported two large openings, which likely means the frill wasn’t useful as a shield. This structure may’ve been used for visual display. In addition to its frill, Torosaurus also possessed a pair of long, curving brow horns and a smaller nasal horn above its beak. In general, its appearance was very similar to that of the famous Triceratops, which it seems to have coexisted with.

Some paleontologists speculate that Torosaurus wasn’t really a distinct genus at all, but the mature form of Triceratops. Those who support this idea contend that the frill, which on Triceratops was a lot shorter and solid, without large openings, would grow quickly over the last stage of its life, into that seen on Torosaurus. Of course, if this were true, then Torosaurus would be a junior synonym of Triceratops, since Triceratops was described and named first. Fossil evidence, however, suggests the two were probably distinct, but closely related taxa. Torosaurus and Triceratops were about the same size, so such a radical change so late is quite strange. Fossils in Canada may represent the juvenile stage of Torosaurus, with traits proving it was a separate taxon. Both are classified within the subfamily Chasmosaurinae and the tribe Triceratopsini. Other dinosaurs in their shared region included Edmontosaurus, Ankylosaurus and Tyrannosaurus. Torosaurus was formally described as a genus in 1891 by Othniel C. Marsh, who also described Triceratops. Its name means “perforated lizard”, referring to its frill openings, which in life were covered by flesh and scales.