Structure of the brain cavity and inner ear of the centrosaurine ceratopsid dinosaur Pachyrhinosaurus based on CT scanning and 3D visualization
Lawrence M. Witmer, Ryan C. Ridgely, 2008. "Structure of the brain cavity and inner ear of the centrosaurine ceratopsid dinosaur Pachyrhinosaurus based on CT scanning and 3D visualization", A New Horned Dinosaur from an Upper Cretaceous Bone Bed in Alberta, Philip J. Currie, Wann Langston, Jr., Darren H. Tanke
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Information on the structure of the brain, cranial nerves, encephalic vasculature, and inner ear of the centrosaurine ceratopsid dinosaur Pachyrhinosaurus lakustai (Upper Cretaceous, Wapiti Formation, Alberta, Canada) is presented based on computed tomographic scanning of an isolated braincase followed by 3D visualization. The resulting digital cranial endocast and endosseous labyrinth are the most complete for any ceratopsid, to date, and are compared with physical and digital endocasts of other ceratopsians. In general, the structure of the brain of P. lakustai, as inferred from the endocast, was relatively primitive and much more like extant nonavian diapsid endocasts than like endocasts of archosaur groups with derived brains, such as pterosaurs, hadrosaurs, or coelurosaurs (including extant birds). Total brain size is relatively small, and none of the externally discernable brain regions (e.g., olfactory bulbs, cerebrum, cerebellum, optic lobes) are expanded. Currently, there are insufficient data to determine whether the simple structure and small size of the brain of P. lakustai are truly plesiomorphic or represent apomorphic reduction (evolutionary reversal). The endosseous labyrinth reveals a short cochlea, suggesting that airborne sounds were not particularly important behaviorally. The semicircular canals of the labyrinth are actually somewhat more elongate compared with what little is known of other neoceratopsian labyrinths. The fossil specimen is slightly compressed transversely, and this plastic deformation was subsequently ameliorated by a simple digital retrodeformation that provides a realistic view of brain size and shape. The most significant biological result of the project is that, even accounting for any deformation, the sensorineural and cognitive capabilities of Pachyrhinosaurus were modest, certainly in comparison with some other dinosaur clades, such as hadrosaurids and coelurosaurian theropods.
An animation of the 3D visualization of the digital endocast is available on NRC Research Press’ Website at http://pubs.nrc-cnrc.gc.calenglbooks/books/9780660198194.html
Key words: Dinosauria, Ceratopsia, Pachyrhinosaurus, brain, behavior, endocast, CT scanning.
Figures & Tables
October 1, 2008, Philip J. Currie, Wann Langston, Jr., and Darren H. Tanke unveiled for the first time the name of a newly discovered horned dinosaur species.
In the first monographic treatment of a horned (ceratopsid) dinosaur in almost a century, this monumental volume presents one of the closest looks at the anatomy, relationships, growth and variation, behavior, ecology and other biological aspects of a single dinosaur species. The research, which was conducted over two decades, was possible because of the discovery of a densely packed bone bed near Grande Prairie, Alberta. The locality has produced abundant remains of a new species of horned dinosaur (ceratopsian), and parts of at least 27 individual animals were recovered.
This new species of Pachyrhinosaurus is closely related to Pachyrhinosaurus canadensis, which is known from younger rocks near Drumheller and Lethbridge in southern Alberta, but is a smaller animal with many differences in the ornamental spikes and bumps on the skull. The adults of both species have massive bosses of bone in the positions where other horned dinosaurs (like Centrosaurus and Triceratops) have horns. However, juveniles of the new species resemble juveniles of Centrosaurus in having horns rather than bosses. Skull anatomy undergoes remarkable changes during growth and the horns over the nose and eyes of the Pachyrhinosaurus juveniles transform into bosses; spikes and horns develop on the top of and at the back of the frill that extends back over the neck. No cause has been determined for the apparent catastrophic death of the herd of Pachyrhinosaurus from the Grande Prairie area, but it has been suggested that such herds may have been migratory animals.
In addition to the main descriptive paper, the volume includes information on the distribution of bones within the bone bed itself, and a cutting-edge digital treatment of CT-scan data of the fossils to reveal the anatomy of the animal’s brain!
See below to view the Pachyrhinosaurus braincase, fading away to reveal the brain within. Courtesy of Witmer & Ridgely, Ohio University.