How Did Vertebrates First Evolve Jaws?
Published:06 Jul.2022 Source:Keck School of Medicine of USC
In the studies, Mathi Thiruppathy from Gage Crump's laboratory at USC, and collaborator J. Andrew Gillis from the University of Cambridge and the Marine Biological Laboratory, looked to embryonic development as way to gain insight into evolution -- an approach known as "evo-devo." In fishes, jaws share a common developmental origin with gills. During development, jaws and gills both arise from embryonic structures called "pharyngeal arches." The first of these arches is called the mandibular arch because it gives rise to jaws, while additional arches develop into gills. There are also anatomical similarities: the gills are supported by upper and lower bones, which could be thought of as analogous to the upper and lower jaws.
"These developmental and anatomical observations led to the theory that the jaw evolved by modification of an ancestral gill," said Thiruppathy, who is the eLife study's first author and a PhD student in the Crump Lab. "While this theory has been around since the late 1800s, it remains controversial to this day." In the absence of clear fossil evidence, the eLife publication presents "living" evidence in support of the theory that jaws originated from gills. Nearly all fishes possess a tiny anatomical structure called a "pseudobranch," which resembles a vestigial gill. However, this structure's embryonic origin was uncertain.