Summary: A new study examines the link between brain development and the bones of the skull roof during the evolutionary transition from dinosaur to bird.
The dramatic, dinosaur-to-bird transition that occurred in reptiles millions of years ago was accompanied by profound changes in the skull roof of those animals — and holds important clues about the way the skull forms in response to changes in the brain — according to a new study.
It is the first time scientists have tracked the link between the brain’s development and the roofing bones of the skull. The findings appear in the Sept. 11 edition of the journal Nature Ecology and Evolution.
“Across the dinosaur-bird transition, the skull transforms enormously and the brain enlarges. We were surprised that no one had directly addressed the idea that the underlying parts of the brain — the forebrain and midbrain — are correlated or somehow developmentally related to the overlying frontal and parietal bones,” said co-senior author Bhart-Anjan Singh Bhullar, an assistant professor of geology and geophysics at Yale University and assistant curator of vertebrate paleontology and vertebrate zoology at the Yale Peabody Museum of Natural History.
Matteo Fabbri, a graduate student in Bhullar’s lab, is the first author of the study. “Our paper is a milestone in the way of approaching the morphological transition from reptile and dinosaur ancestors to extant birds,” Fabbri said.
Although previous studies have shown a general relationship between the brain and skull, associations between specific regions of the brain and individual elements of the skull roof have remained unclear. This has led to conflicting theories on some aspects of skull development.
Bhullar and his colleagues set out to trace the evolution of brain and skull shape not simply in the dinosaurs closest to birds, but in the entire lineage leading from reptiles to birds. They discovered that most reptile brains and skulls were markedly similar to each other. It was the dinosaurs most closely related to birds, as well as birds themselves, that were divergent, with enlarged brains and skulls ballooning out around them.
“We found a clear relationship between the frontal bones and forebrain and the parietal bones and midbrain,” Bhullar said. The researchers confirmed this finding by looking at embryos of lizards, alligators, and birds using a new contrast-stained CT scanning technique.
“We suggest that this relationship is found across all vertebrates with bony skulls and indicates a deep developmental relationship between the brain and the skull roof,” Bhullar said. “What this implies is that the brain produces molecular signals that instruct the skeleton to form around it, although we understand relatively little about the precise nature of that patterning.”
Bhullar added: “Ultimately, one of the important messages here is that evolution is simpler and more elegant than it seems. Multiple seemingly disparate changes — for instance to the brain and skull — could actually have one underlying cause and represent only a single, manifold transformation.”
About this neuroscience research article
Arhat Abzhanov of Imperial College London is the paper’s other co-senior author.
Yale co-authors are Nicolas Mongiardino Koch, Adam Pritchard, Michael Hanson, and Eva Hoffman. Additional co-authors include researchers from Johns Hopkins University School of Medicine, Harvard University, the University of Bath, the American Museum of Natural History, Iziko South African Museum, and the University of Texas-Austin.
Funding: Yale, Imperial College London, and grants from the National Science Foundation and the Templeton Foundation funded the research.
Source: Jim Shelton – Yale Image Source: NeuroscienceNews.com image is credited to the researchers. Original Research:Abstract for “The skull roof tracks the brain during the evolution and development of reptiles including birds” by Matteo Fabbri, Nicolás Mongiardino Koch, Adam C. Pritchard, Michael Hanson, Eva Hoffman, Gabriel S. Bever, Amy M. Balanoff, Zachary S. Morris, Daniel J. Field, Jasmin Camacho, Timothy B. Rowe, Mark A. Norell, Roger M. Smith, Arhat Abzhanov & Bhart-Anjan S. Bhullar in Nature Ecology and Evolution. Published online September 11 2017 doi:10.1038/s41559-017-0288-2
Cite This NeuroscienceNews.com Article
[cbtabs][cbtab title=”MLA”]Yale “Scientists Track the Brain-Skull Transition from Dinosaurs to Birds.” NeuroscienceNews. NeuroscienceNews, 11 September 2017. <https://neurosciencenews.com/dionosaur-bird-skull-transition-7463/>.[/cbtab][cbtab title=”APA”]Yale (2017, September 11). Scientists Track the Brain-Skull Transition from Dinosaurs to Birds. NeuroscienceNew. Retrieved September 11, 2017 from https://neurosciencenews.com/dionosaur-bird-skull-transition-7463/[/cbtab][cbtab title=”Chicago”]Yale “Scientists Track the Brain-Skull Transition from Dinosaurs to Birds.” https://neurosciencenews.com/dionosaur-bird-skull-transition-7463/ (accessed September 11, 2017).[/cbtab][/cbtabs]
Major transformations in brain size and proportions, such as the enlargement of the brain during the evolution of birds, are accompanied by profound modifications to the skull roof. However, the hypothesis of concerted evolution of shape between brain and skull roof over major phylogenetic transitions, and in particular of an ontogenetic relationship between specific regions of the brain and the skull roof, has never been formally tested. We performed 3D morphometric analyses to examine the deep history of brain and skull-roof morphology in Reptilia, focusing on changes during the well-documented transition from early reptiles through archosauromorphs, including nonavian dinosaurs, to birds. Non-avialan taxa cluster tightly together in morphospace, whereas Archaeopteryx and crown birds occupy a separate region. There is a one-to-one correspondence between the forebrain and frontal bone and the midbrain and parietal bone. Furthermore, the position of the forebrain–midbrain boundary correlates significantly with the position of the frontoparietal suture across the phylogenetic breadth of Reptilia and during the ontogeny of individual taxa. Conservation of position and identity in the skull roof is apparent, and there is no support for previous hypotheses that the avian parietal is a transformed postparietal. The correlation and apparent developmental link between regions of the brain and bony skull elements are likely to be ancestral to Tetrapoda and may be fundamental to all of Osteichthyes, coeval with the origin of the dermatocranium.
“The skull roof tracks the brain during the evolution and development of reptiles including birds” by Matteo Fabbri, Nicolás Mongiardino Koch, Adam C. Pritchard, Michael Hanson, Eva Hoffman, Gabriel S. Bever, Amy M. Balanoff, Zachary S. Morris, Daniel J. Field, Jasmin Camacho, Timothy B. Rowe, Mark A. Norell, Roger M. Smith, Arhat Abzhanov & Bhart-Anjan S. Bhullar in Nature Ecology and Evolution. Published online September 11 2017 doi:10.1038/s41559-017-0288-2