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Are Torosaurus and Triceratops one and the same?

This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American


A rare horned dinosaur known as Torosaurus may not be a distinct species, after all, according to a presentation given Friday at the annual meeting of the Society of Vertebrate Paleontology in Bristol, England.

Researchers have long recognized similarities between Torosaurus and Triceratops, the main distinctions being that Torosaurus is larger and has an expanded frill at the rear of the skull. But John Scannella, a doctoral student at Montana University, and his advisor, John R. Horner, have found that specimens attributed to the two species actually form a developmental continuum rather than falling into discrete groups. A Triceratops skeleton on display at the American Museum of Natural History in New York City, for example, exhibits a number of skull traits reminiscent of Torosaurus, including thin parietal bones and elongated squamosal bones. In addition, microscope examinations of thin slices of bone from Triceratops and Torosaurus specimens reveal that individuals attributed to Torosaurus are more mature than any of the ones assigned to Triceratops. Scannella and Horner therefore believe that the fossils that have been categorized as Torosaurus are just Triceratops individuals that reached mature adulthood before they died.


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Scientists have wondered how two such similar groups could have shared the landscape—both ranged from Colorado to Saskatchewan at the end of the Cretaceous period. If Scanella and Horner are right, the answer is simply that the animals are one and the same species.

But the finding raises the question of why fossil hunters have recovered so few of the mature “Torosaurus” specimens—fewer than a dozen, compared to the many dozens of younger Triceratops. “If Torosaurus is Triceratops, then we’re finding a lot of animals that had a lot of growing up to do,” Scannella comments. Insights may come once researchers determine a more precise age at death for the individuals.

The finding provides more evidence that dinosaur diversity was declining before the animals became extinct, which, Scannella says, supports the idea that something other than an asteroid impact extinguished them.

 

Photo of Triceratops skeleton at the American Museum of Natural History by mrkathika via Flickr

Kate Wong is an award-winning science writer and senior editor at Scientific American focused on evolution, ecology, anthropology, archaeology, paleontology and animal behavior. She is fascinated by human origins, which she has covered for more than 25 years. Recently she has become obsessed with birds. Her reporting has taken her to caves in France and Croatia that Neandertals once called home, to the shores of Kenya's Lake Turkana in search of the oldest stone tools in the world, to Madagascar on an expedition to unearth ancient mammals and dinosaurs, to the icy waters of Antarctica, where humpback whales feast on krill, and on a "Big Day" race around the state of Connecticut to find as many bird species as possible in 24 hours. Kate is co-author, with Donald Johanson, of Lucy's Legacy: The Quest for Human Origins. She holds a bachelor of science degree in biological anthropology and zoology from the University of Michigan. Follow Wong on X (formerly Twitter) @katewong

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