Triceratops and similar horned dinosaurs had unusually large nasal cavities compared to most animals. Researchers including those from the University of Tokyo used CT scans of fossilized Triceratops skulls and compared their structures with modern animals like birds and crocodiles. Through direct observation and inference, researchers reconstructed how nerves, blood vessels and structures for airflow fit together in the skulls. They concluded horned dinosaurs probably used their noses not just for smelling but also to help control temperature and moisture.
If you spot a Triceratops in the wild, it may raise a question or two: firstly, "Aren't they extinct?” and secondly, “Why does it have such an enormous head?" Project Research Associate Seishiro Tada from the University of Tokyo Museum wondered about the latter while looking at 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 exhibited a wide range of skull types contributing to their visual diversity, which is part of their appeal. Horned dinosaurs, or Ceratopsia, had some of the more elaborate skulls, with Triceratops’ being iconic and instantly recognizable. But due to its relative uniqueness, the internal anatomy of Triceratops skulls is also poorly understood. So, Tada and his team set out to explore the internal soft tissues using the tools at their disposal.
“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 researchers also found a special structure in Triceratops’ nose called a respiratory turbinate, which almost no other dinosaurs are known to possess, though their living descendants, the birds, do, as do mammals. These structures are thin, curled surfaces within the nose that increase the surface area for blood and air to exchange heat. Triceratops probably wasn’t fully warm-blooded, but the researchers think these structures helped keep temperature and moisture levels under control as its large skull would be difficult to cool down otherwise.
“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.”
