Triceratops and other horned dinosaurs had exceptionally large nasal cavities compared to most animals. To better understand what filled that space, researchers including a team from the University of Tokyo analyzed CT scans of fossilized Triceratops skulls. They compared those scans with the snout anatomy of living animals such as birds and crocodiles. By combining direct examination with informed reconstruction, they mapped out how nerves, blood vessels, and air passages likely fit inside the skull. Their findings suggest these dinosaurs used their noses for more than smell. The oversized nasal passages may also have helped regulate body temperature and moisture.
If you were to encounter a Triceratops in the wild, you might first ask, “Aren’t they extinct?” and then wonder, “Why does it have such an enormous head?” Project Research Associate Seishiro Tada from the University of Tokyo Museum found himself focused on that second question while studying a specimen (a fossilized one). “I have been working on the evolution of reptilian heads and noses since my master’s degree,” he said. “Triceratops in particular had a very large and unusual nose, and I couldn’t figure out how the organs fit within it even though I remember the basic patterns of reptiles. That made me interested in their nasal anatomy and its function and evolution.”
Dinosaurs came in many shapes and sizes, and their skulls were especially diverse. Horned dinosaurs, known as Ceratopsia, had some of the most dramatic head structures, and Triceratops stands out as one of the most recognizable. Yet despite its fame, scientists still know relatively little about what the inside of its skull looked like. Tada and his colleagues set out to reconstruct the soft tissues hidden within the fossilized bone.
CT Scans Reveal Unusual Nasal Wiring
“Employing X-ray-based CT-scan data of a Triceratops, as well as knowledge on contemporary reptilian snout morphology, we found some unique characteristics in the nose and provide the first comprehensive hypothesis on the soft-tissue anatomy in horned dinosaurs,” he said. “Triceratops had unusual ‘wiring’ in their noses. In most reptiles, nerves and blood vessels reach the nostrils from the jaw and the nose. But in Triceratops, the skull shape blocks the jaw route, so nerves and vessels take the nasal branch. Essentially, Triceratops tissues evolved this way to support its big nose. I came to realize this while piecing together some 3D-printed Triceratops skull pieces like a puzzle.”
The team discovered that the structure of the skull forced nerves and blood vessels to follow a different pathway than in most reptiles. Instead of entering through the jaw, they traveled through the nasal region. This rearranged internal layout appears to have evolved to accommodate and support the dinosaur’s exceptionally large nose.
Evidence of Respiratory Turbinates and Heat Control
Researchers also identified signs of a structure known as a respiratory turbinate inside the nose of Triceratops. Very few dinosaurs show evidence of this feature, although birds, which are living descendants of dinosaurs, have them, as do mammals. Respiratory turbinates are thin, scroll shaped bones inside the nasal cavity that increase surface area, allowing blood and air to exchange heat more efficiently.
Triceratops was likely not fully warm blooded, but these structures may still have played an important role in controlling temperature and retaining moisture. Given the size of its skull, managing heat would have been a challenge. The presence of respiratory turbinates suggests its nose helped stabilize internal conditions.
“Although we’re not 100% sure Triceratops had a respiratory turbinate, as most other dinosaurs don’t have evidence for them, some birds have an attachment base (ridge) for the respiratory turbinate and horned dinosaurs have a similar ridge at the similar location in their nose as well. That’s why we conclude they have the respiratory turbinate as birds do,” said Tada. “Horned dinosaurs were the last group to have soft tissues from their heads subject to our kind of investigation, so our research has filled the final piece of that dinosaur-shaped puzzle. Next, I would like to tackle questions around the anatomy and function of other regions of their skulls like their characteristic frills.”
Funding: Japan Society for the Promotion of Science (JSPS) KAKENHI, 24KJ1879; JSPS Overseas Challenge Program for Young Researchers.