Paleontologists have discovered a shocking fact about the relationship between the celebrated Triceratops dinosaur (left) and its less-glamorous, holey-headed counterpart, Torosaurus (right). Turns out they're not evolutionary cousins. In fact, Triceratops is just a younger version of Torosaurus.
Paleontologists Jack Horner and John Scannella published a paper this week in Journal of Vertebrate Paleontology that overturned long-held beliefs about the famous Triceratops and Torosaurus, both discovered in the late nineteenth century. Until recently, scientists believed they were related species, but Horner and Scannella took a hard look at the creatures' fossils and discovered they were in fact seeing the maturation phases of the same animal.
According to Brian Switek, writing for the Smithsonian:
After collecting and examining dozens of specimens, the paleontologists found a graded continuum of growth from the smallest juvenile Triceratops all the way up to what has been called Torosaurus. (The difficult-to-classify specimen representing the genus Nedoceratops may also fall within this range of skull shapes.) On the basis of gross anatomy alone, it is easily seen how the frill of Triceratops changed as it aged, with large windows in the frill opening up as the dinosaur became an adult. But some of the most compelling evidence for these changes comes from bone anatomy that can be seen only under a microscope.
When Horner and Scanella looked at the bone structure of Triceratops brow horns, they found that what had previously been thought to be fully mature individuals still had some growing to do. These Triceratops specimens lacked the amount of dense, mature bone which would have been expected for a fully grown animal, and, instead, this kind of mature bone was found in the horns of Torosaurus. Since all the specimens identified as Torosaurus represent adults, and what were thought to be fully adult Triceratops are only young adults, the simplest explanation is that both are growth stages of Triceratops (which was named first, and therefore has priority for the genus name).
From what Scannella and Horner were able to tell, Triceratops retained juvenile characteristics (such as a solid frill) for most of its life before a rapid change before reaching maturity.
Because the Triceratops was named first, that designation will be kept and the name Torosaurus stricken from the records. Farewell, Torosaurus.