Common Language Summary
Paradox revealed? The simple brain of a seemingly complex dinosaur. Horned dinosaurs (ceratopsians) give the appearance of having had sophisticated social interactions, with heads adorned with sometimes elaborate horns, frills, and other display structures. But did they have the brain power needed for sophisticated behaviors? The Pipestone Creek bone bed of west-central Alberta provides a unique glimpse into the biology of a new ceratopsian species. Pachyrhinosaurus lakustai is represented by hundreds of bones from individuals of diverse ages that perished more or less together and were transported to their final resting place, later to be entombed in 73-million-year-old Upper Cretaceous rocks. The isolated bony braincase of a subadult individual was CT scanned and analyzed using advanced computer 3D-visualization software. The resulting “virtual brain” in some ways doesn’t look much like a brain, because the brain itself was too small to impress its form into the bony walls that surrounded it. Indeed, the most remarkable aspect of the brain structure of Pachyrhinosaurus is how small and primitive it must have been. There is no evidence for any marked expansion of the neural centers of smell (olfactory bulbs), vision (optic lobes), motor coordination (cerebellum), or higher cognitive function (cerebrum). Likewise, the relatively short cochlea of the inner ear suggests that hearing air-borne sounds was not especially important for Pachyrhinosaurus . The small, primitive cerebral hemispheres are particularly interesting, because in modern animals these are the seat of higher behavioral functions such as learning and problem-solving. They are so small in Pachyrhinosaurus that it is tempting to question how sophisticated its behavioral repertoire could have been. Despite the cranial ornaments suggestive of perhaps elaborate behavioral displays and other evidence suggesting herding behavior or even migration, the behaviors of Pachyrhinosaurus were probably relatively simple, stereotyped, and instinctual.