Researchers at the University of Bristol in the United Kingdom have managed to digitally reconstruct the jaw of precursor species of mammals, from Brazilian fossils of Brasilodon quadrangularis and Riograndense guaibensis. The findings, published in the renowned scientific journal Nature on Wednesday (25), were important in revealing evolutionary experiments that occurred millions of years earlier than previously thought.
Mammals stand out among vertebrates for having a distinct jaw structure and the presence of three middle ear bones. The evolutionary process that led to the development of these characteristics has long fascinated scientists, and now, with the new studyit was possible to understand how mammalian ancestors, known as cynodonts, developed two more middle ear bones than the vertebrates before them.
Using computed tomography, researchers have digitally reconstructed the jaw joint of these cynodonts for the first time. They found that there is a typical mammalian connection between the skull and the lower jaw in Riograndense guaibensisa species of cynodont that lived 17 million years before the oldest species known to have this structure.
However, researchers did not find the same link in a Brasilodon quadrangularisa species more closely related to mammals. This indicates that the defining characteristic of the mammalian jaw evolved multiple times in different cynodont groups, earlier than expected.
These findings suggest that mammalian ancestors experimented with different jaw functions, leading to the evolution of “mammalian traits” independently in multiple lineages. The new findings indicate that mammalian evolution may have been more complex and varied than scientists previously believed.
“The acquisition of mammalian jaw contact was a key moment in mammalian evolution,” explains lead author James Rawson, from Bristol’s School of Earth Sciences. “What these new Brazilian fossils have shown is that different groups of cynodonts were experimenting with multiple types of jaw joints, and that some features previously thought to be exclusively mammalian have evolved multiple times in other lineages too.”
“Nowhere else in the world is there such a diverse range of cynodont forms, closely related to the first mammals,” adds Professor Marina Soares, from the National Museum, linked to the Federal University of Rio de Janeiro (URFJ).
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This content was originally published in Brazilian fossils reveal unexpected discovery about the evolution of mammals on the CNN Brasil website.
Source: CNN Brasil
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