New study uses CT scans to explore inner structure of lambeosaur skulls
A new study led by Dr. David Evans, Associate Curator of Vertebrate Palaeontology at the Royal Ontario Museum (ROM), reveals that the large, bizarre-shaped crests of duck-bill dinosaurs called lambeosaurs were used as a means of communication. The study combined 3D imaging, growth studies, and phylogenetic sampling to reconstruct the first ever detailed look into the brain and inner ear in this group of dinosaurs. The results of the study were presented on October 17 at the annual meeting of The Society of Vertebrate Palaeontology, and will be published in part in an upcoming issue of the journal The Anatomical Record.
The strange bony crests found in the skulls of these duck-billed dinosaurs come in a variety of sizes and shapes. These crests contain incredibly long, convoluted nasal passages that loop up over the tops of their skulls. Without any modern animal with similar structures, palaeontologists have long debated the function of the crests. Some suggested that they heightened the sense of smell by increasing the surface area of the sensory tissue, others that they functioned in temperature regulation, and still others that the crests acted as sound resonators for communication.
Dr. Evans and colleagues from Ohio University and Montana State University used CT-scanning to look inside the passages and cavities in the skulls and reconstruct the brains and nasal cavities of four different lambeosaur species. “The shape of the brain can tell us a lot about what senses were important in a dinosaur’s everyday life, and give insight into the function of the crests.” said Dr. Evans.
With the CT scans, Evans and his team were able to circumvent the problems of fossilization. “Even though the soft tissues are not preserved in the fossils, the shape of the bones that encase the brain and nasal passages are,” said Dr. Evans. “From there, the anatomy of these missing soft parts is easily interpreted.”
The CT scan results revealed a mismatch between the external shape of the crest (which no doubt functioned as a visual display) and the internal shape of the nasal passages in closely related species, suggesting a special function for the nasal cavity. The portion of the brain responsible for the sense of smell was relatively small and primitive, indicating that the crest did not evolve to improve the sense of smell. Computer models done by other researchers suggest that the crests could have been used to make low, eerie bellowing calls that could have been used in communication, perhaps to call for mates or warn others of predators. The CT scans documented a delicate inner ear that confirms that the dinosaurs could hear the low-frequency calls produced by the crest.
Co-authors on the study include David C. Evans, Department of Natural History, Royal Ontario Museum, Lawrence M. Witmer and Ryan C. Ridgely of Ohio University in Athens, Ohio, and John R. Horner from Montana State University in Bozeman, Montana. This project was supported by grants from the National Science and Engineering Research Council of Canada and the National Science Foundation.