MESOZOIC ORIGIN OF THE BONE-EATING OSEDAX WORMS AND INSIGHTS ON THE ORIGIN OF THE SIBOGLINIDAE (ANNELIDA)
Here we report the first fossil evidence of Osedax traces on early Late Cretaceous (~ 100 Myr) plesiosaur and sea turtle bones, which supports a pre-Cenozoic origin of the clade. Whereas plesiosaurs went extinct at the Cretaceous-Tertiary boundary, chelonioids survived to the event, representing available substrates for Osedax in the 20 Myr gap preceding the radiation of cetaceans. This finding shows that marine reptile carcasses, before whales, played a key role in the evolution and dispersal of Osedax and confirms that its generalist ability of colonizing different vertebrate substrates, like fishes and marine birds, besides whale bones, is an ancestral trait. A Cretaceous age for Osedax trace fossils also dates back to the Mesozoic the origin of the entire siboglinid family, which includes chemosynthetic tubeworms living at hydrothermal vents and seeps, contrary to phylogenetic estimations of a Late Mesozoic–Cenozoic origin (approx. 50–100 Myr).