A team of researchers reporting in the journal Nature has revealed that some non-avian dinosaurs had brains that were as large or larger than that of Archaeopteryx lithographica, one of the earliest known birds, indicating that some dinosaurs already suspected of possessing flight capability would have had the neurological hardwiring necessary for this behavior.
Archaeopteryx lithographica, one of the earliest known birds (Carl Buell / Nicholas Longrich).
“Archaeopteryx has always been set up as a uniquely transitional species between feathered dinosaurs and modern birds, a halfway point. But by studying the cranial volume of closely related dinosaurs, we learned that Archaeopteryx might not have been so special,” said first author Dr Amy Balanoff of the American Museum of Natural History.
Using CT scanners, the team peered inside the braincases of more than twenty specimens, including modern birds, Archaeopteryx, and closely related non-avian dinosaurs. By stitching together the CT scans, they created 3D reconstructions of the skulls’ interiors. In addition to calculating the total volume of each digital brain cast, they also determined the size of each brain’s major anatomical regions, including the olfactory bulbs, cerebrum, optic lobes, cerebellum, and brain stem.
“The story of brain size is more than its relationship to body size. If we also consider how the different regions of the brain changed relative to each other, we can gain insight into what factors drove brain evolution as well as what developmental mechanisms facilitated those changes,” said co-author Dr Gabriel Bever from the New York Institute of Technology.
The brain cast of Archaeopteryx lithographica partitioned into neuroanatomical regions: brain stem – yellow, cerebellum – blue, optic lobes – red, cerebrum – green, and olfactory bulbs – orange (© AMNH / A. Balanoff).
The team found that in terms of volumetric measurements, Archaeopteryx is not in a unique transitional position between non-avian dinosaurs and modern birds.
Several other non-avian dinosaurs, including bird-like oviraptorosaurs and troodontids, actually had larger brains relative to body size than Archaeopteryx.
Dr Balanoff said: “if Archaeopteryx had a flight-ready brain, which is almost certainly the case given its morphology, then so did at least some other non-avian dinosaurs.”
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Bibliographic information: Amy M. Balanoff et al. Evolutionary origins of the avian brain. Nature, published online July 31, 2013; doi: 10.1038/nature12424
