The brain and ear of Pachyrhinosaurus, a Cretaceous horned dinosaur from Canada
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.
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