Millions of years after its extinction, Triceratops is inciting controversy about how to classify the ancient animals. New analysis, published Feb. 29 in the open access journal PLoS ONE, suggests that the specimens in question should be classified into two separate groups, Triceratops and Torosaurus, and are not individuals of different ages from the same genus, as others have proposed.
The researchers, led by Nicholas Longrich of Yale University, performed detailed morphological and computational analysis of 35 specimens and found evidence that Triceratops and Torosaurus should be considered distinct. In particular, the researchers aged skulls by looking at the closing of sutures between skull bones. They found evidence that some Torosaurus skulls were immature, and some Triceratops skulls were adult, which was inconsistent with the idea that skulls assigned to Torosaurus represented adult Triceratops. This result is in contrast to a hypothesis from a different group that suggests they actually represent juvenile and adult specimens from the same genus.