Artist's impression of Microbrachius mating sceneBRIAN CHOO, FLINDERS UNIVERSITYIt is widely believed that external fertilization—like frogs spawning in pools—is the ancestral mode of reproduction among jawed vertebrates; internal fertilization—typically involving some form of sex—is thought to have evolved later. But the discovery of certain structures indicative of internal fertilization in the 400 million-year-old fossils of Microbrachius, which were among the first jawed fish, shakes the very foundation of this claim.
“It would not take a whole lot of evidence to reshape that tree to suggest a different history,” said evolutionary biologist Martin Brazeau of Imperial College London who was not involved in the study, which was published today (October 19) in Nature. “But I think that’s part of what makes this a really exciting discovery. It’s going to drive a lot of debate and I think it’s one of the most important discoveries in this area of research in years.”
“Internal fertilization might be even more widespread than implied by these fossils, because it doesn’t always have an obvious morphological (anatomical) signature,” Michael Coates from the University of Chicago who was also not involved with the research said in an e-mail.
Microbrachius is an “antiarch,” ...
