Expanding the Triceratops Family Tree

by Katie Bowell, Curator of Cultural Interpretation

Meet Triceratops, a dinosaur with three horns and a short frill on its head.

Triceratops Skeleton

Meet Torosaurus, a dinosaur with a large, two-holed frill on its head.

Torosaurus Skeleton

They look like different species, don’t they (especially with the differences in their frills)? Well, it turns out, they might not be…

Since the late 1800s, paleontologists thought Triceratops and Torosaurus were two separate species. But now, some paleontologists think that Torosaurus is just an old Triceratops.

After studying dinosaur skulls for years, paleontologists John Scannella and Jack Horner at Montana State University noticed something strange: Triceratops skulls were always from younger individuals, and Torosaurus skulls were always from older ones. The fossil record is spotty, but probably not so spotty that no individuals of a specific age group would ever appear to be preserved. Unless, of course, the species’ appearance changes so dramatically as it grows that a juvenile and an adult of the same species look like two different species.

This isn’t a new idea in science; in fact, it happens a lot. Think about caterpillars and butterflies, tadpoles and bullfrogs. Because we’re able to observe these animals developing, the extreme physiological changes (though still surprising and fascinating) make sense. Dinosaurs and other prehistoric organisms can only be observed through the fossil record, which makes understanding physical changes from birth to death much more difficult.

Scannella and Horner examined Triceratops and Torosaurus skulls from museums around the world, and found evidence that Torosaurus may be Triceratops at later growth stages, rather than a separate species. The researchers measured skull length, width and thickness, and also examined the microstructure, surface textures and shape changes of the frills. These analyses revealed that the Triceratops and Torosaurus specimens came from the same species and that tissues of Torosaurus were heavily remodeled compared to Triceratops, which is what happens as bones continue to grow.

Left: Younger Triceratops; Right: Older "Torosaurus"

So what’s going to happen to Triceratops and Torosaurus now? Well, if continued research provides sufficient evidence to convince the scientific community that Triceratops and Torosaurus are one and the same, the name Triceratops, which was coined before Torosaurus, will be applied. Thank goodness; I’m still coming to terms with the demotion of Brontosaurus!

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2 Responses to “Expanding the Triceratops Family Tree”


  1. 1 Panzerraptor December 7, 2010 at 5:17 pm

    Yeah, I get where you’re going. But I think to “Torosaurus” skeleton you’re using is actually Pentaceratops. Just throwing it out there.

  2. 2 Katie December 8, 2010 at 3:19 pm

    Very interesting. The museum label says “Torosaurus,” which is why we used the image. What about the skeleton’s appearance is making you think it’s Pentaceratops instead?


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