The process by which some dinosaurs became birds millions of years ago was accompanied by profound changes in the upper part of the skull of those reptiles, according to a study published this Monday in the journal Nature. The research led by experts from Yale University (USA) also provides new clues on how skulls evolve according to the transformations that pass through the brains, an unexplored area until now in this field. "During the transition from dinosaur to bird, the skull is transformed enormously and the brain is enlarged. We were surprised that no one had directly studied this idea," explained Bhart-Anjan Singh Bhullar, one of the study authors. According to this approach, the anterior (prosencephalon) and middle (mesencephalon) brains are related or "developmentally connected" to the frontal and parietal bones of the skull, the expert said. Although previous studies have addressed the general connection between the brain and skull, it was not clear until now that there are relationships between specific regions of the brain and individual elements of the upper skull. This, the Yale scientists said, has led to opposing theories about the developmental processes of the skull. In this sense, Bhullar and his colleagues did not simply analyze the evolution of the brain and cranial morphology of the dinosaurs closest to the birds, but addressed that of the entire lineage involved in the transition from reptiles to birds. They found that most reptile brains and skulls were markedly similar to each other, while those of dinosaurs and evolutionarily closer birds were different. "We found a clear relationship between the frontal bones and the prosencephalon and between the parietal bones and the midbrain," said Bhullar, whose team analyzed embryos from lizards, caimans and birds for this research. The experts suggest that this relationship "exists in all vertebrates with bony skulls" and points to a "deep developmental connection" between the brain and the upper skull. "This implies that the brain produces molecular signals that force the skeleton to form around it," said Bhullar, who acknowledged that "we know relatively little about the precise nature of this pattern. Ultimately, he concluded, one of the conclusions of this study is that "evolution is simpler and more elegant than it seems.
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January 2019
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