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    584—Vocal Communication: Non-Avian

    Tuesday, November 12, 2013, 8:00 am - 12:00 noon

    584.11: Inferred organization of a dinosaur brain

    Location: Halls B-H

    *C.-C. CHEN1, K. WADA3, M. V. RIVAS4, E. JARVIS2, D. SOARES5, D. FRIEDEBERG2, T. GLENN6, E. D. JARVIS2;
    1Neurogiology, 2Neurobio., Duke Univ., Durham, NC; 3Biol. Sci., Hokkaido Univ., Sapporo, Japan; 4Durham Veteranís Affairs Med. Ctr., Durham, NC; 5Biol., Univ. of Maryland, College Park, MD; 6Envrn. Hlth. Sci., Univ. of Georgia, Athens, GA

    Abstract Body: Because dinosaurs are extinct, no known viable brain material exists. The closest living relatives are crocodiles, which pre-date many dinosaurs, and birds, which post-date them. Therefore, the similarities between the brains of crocodiles and birds would suggest shared organization with dinosaur brains. Here, we used thirteen genes [PPAPDC1A, SEMA6A, FOXP1, FOXP2, SLIT1, COUP-TF2, ER81, LHX9, GRIN2D, GRIN2A, ROR-β, DLX6, LHX8] that we found define seven major cerebral subdivisions of the avian brain, consistent with a new understanding of avian brain organization (Jarvis et al., 2013; Chen et al., 2013), to decipher whether some or most of these regions exists in crocodilian brain. We found six regions in the alligator brain with a similar, but not identical organization as the avian brain. Two of these, the striatum and pallidum, make up the basal ganglia, which we know to be conserved among amniotes. The others include the pallial regions that in birds were recently redefined as the arcopallium, nidopallium, mesopallium, hyperpallium and associated primary sensory pallial fields. These regions in birds contain pathways for vocal learning behavior and other complex behaviors, and like in birds show hearing-induced gene expression when hearing alligator vocalizations. The more highly developed subdivision in birds was the hyperpallium, at the dorsal surface of the brain, which contains one of two visual pathways and somatosensory processing areas. Overall, the molecular topographic organization of the crocodilian cerebrum is about 90% similar to that of birds, including the presence of a relatively large pallium, an analogue of the mammalian cortex. These findings suggest that the brains of dinosaurs must have included a cerebrum with these six subdivisions that have the capacity to process complex, cognitive behaviors.

    Lay Language Summary: Dinosaurs appeared on Earth approximately 230 million years ago, were the dominant terrestrial vertebrates for 135 million years but went extinct around 66 million years ago. By fossil records, such as petrified tissues or trace marks, paleontologists are able to study the morphology of these extinct animals and even infer their movements or other complex behaviors. However, their brains remain mysterious to us and there are lots to be discovered. Brain tissues are soft, rapidly degrade after death, and scavengers rarely leave them intact. For these reasons, it is hard to study an actual dinosaur brain. Here we suggest that we can infer the organization of dinosaur brain by studying the brain structures of their close modern living species. From their brain organization, we can further infer the behaviors of the dinosaurs.
    The closest living relatives of dinosaurs are crocodiles, which pre-date many dinosaurs, and fossil records indicate that birds also evolved from dinosaurs. Therefore, similarities between the brain structures of crocodiles and birds would suggest shared organization with dinosaur brains. We used the molecular profiles and computational analysis to map the telencephalic subdivision of their modern relatives and surprisingly found that the majority of the subdivisions between crocodiles and birds are similar to each other.
    In our study, we compared the thirteen gene profiles indicating different molecular functions of brain subdivions between crocodiles and birds by qualitative expression patterns and quantitative cluster analyses. We found seven major cerebral subdivisions of the avian brain, consistent with a new understanding of avian brain organization, to decipher whether some or most of these regions exists in crocodilian brain. We found six regions in the alligator brain with a similar, but not identical organization as the avian brain. Two of these, the striatum and pallidum, make up the basal ganglia, which we know to be conserved among amniotes. The others include pallial regions that were recently redefined as the arcopallium, nidopallium, mesopallium, and associated primary sensory pallial fields, both in birds and the crocodile. These regions in birds contain pathways for vocal learning behavior and other complex behaviors. The more highly developed subdivision specific to birds was the hyperpallium, at the dorsal surface of the brain, which contains one of two visual pathways and somatosensory processing areas. Interestingly, we found that a global view of telencephalic organization exists between crocodiles and birds. The molecular patterns of their telencephalons revealed a partial mirror image organization of the three major brain subdivisions around the ventricle and adjacent lamina. Additionally, we examined the auditory pathways in crocodiles when hearing its conspecific vocalization regions is similar to the avian auditory pathway.
    Overall, the molecular topographic organization of the crocodilian telencephalon is about 90% similar to that of birds, including the presence of a relatively large pallium, which shares several features with the mammalian cortex. These findings suggest that the brains of dinosaurs are likely to have included a telencephalon with these six subdivisions that have the capacity to process complex cognitive behaviors.