Bone-eating Osedax worms lived on Mesozoic marine reptile deadfalls

Abstract

We report fossil traces of Osedax, a genus of siboglinid annelids that consume the skeletons of sunken vertebrates on the ocean floor, from early-Late Cretaceous (approx. 100 Myr) plesiosaur and sea turtle bones. Although plesiosaurs went extinct at the end-Cretaceous mass extinction (66 Myr), chelonioids survived the event and diversified, and thus provided sustenance for Osedax in the 20 Myr gap preceding the radiation of cetaceans, their main modern food source. 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 unequivocal 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).

Identification of fossil worm tubes from Phanerozoic hydrothermal vents and cold seeps

“…Our study suggests that Late Cretaceous tubes from the Troodos Ophiolite and Early Jurassic tubes from the Figueroa deposit were made by vestimentiferans, which greatly extends the age of this lineage beyond that suggested by molecular clock analyses. This finding is supported by a further piece of independent evidence: the discovery of mid Cretaceous Osedax fossils (Danise & Higgs 2015) suggesting that the more derived siboglinid lineages have a Mesozoic origin. However, we were unable to find definitive evidence that Devonian and Silurian vent fossils were made by siboglinids, thereby reinforcing doubts that this family could extend back into the Palaeozoic (Vrijenhoek 2013) and certainly not back to the Neoproterozoic (Moczyd»owska et al 2014).…”

“…The oldest putative vent siboglinid, Yamankasia rifeia, is »440 million years old, which vastly exceeds the range of molecular age estimates for the family Siboglinidae Caullery, 1914, of 50-126 million years (Little & Vrijenhoek 2003;Vrijenhoek 2013). Recently discovered borings of the bone-eating siboglinid worm Osedax in Late Cretaceous (»100 million year old) plesiosaur and turtle bones (Danise & Higgs 2015), however, suggest that the older molecular age estimates for this family may be more accurate. The above study also highlights that better morphological assessment of fossils is needed to clarify the evolutionary ages of vent and seep fauna.…”

“…The confirmed and suspected presence of siboglinids in many ancient vent and seep deposits is perhaps due to their possession of weedy characteristics such as wide habitat preferences and distant dispersal abilities (Georgieva et al 2015b), which may have enabled them to make use of vent and seep environments repeatedly and over long periods of time. The surprising fossil discoveries of Danise & Higgs (2015) and the reinterpretations presented here emphasize that the evolutionary history of this remarkable family warrants further investigation, and we therefore urge that an earlier origin for the main tube-building vent and seep annelid lineage, the vestimentiferans, be considered and incorporated into a much-needed new molecular age estimation for Siboglinidae.…”

An inordinate fondness for Osedax (Siboglinidae: Annelida): Fourteen new species of bone worms from California

“…Fossil and molecular evidence indicate that the origin of Osedax dates into the Cretaceous period (Danise & Higgs 2015;Taboada et al 2015;Vrijenhoek et al 2009). In this sense Osedax resembles the radiation of vestimentiferans, but no records exist for such high species diversity among vestimentiferan or frenulate siboglinids in comparably small geographic areas as in Monterey Bay.…”

“…There was no obvious difference among species of Osedax for settlement patterns on these experimental substrates versus whale bones (data not shown) although the qualitatively lower densities of worms on experimental substrates often made it much easier to see and collect the 'nude-palp' species. This substrate flexibility was not surprising given that Osedax has been shown to successfully exploit teleost bones (Rouse et al 2011), and fossil evidence indicates they exploited plesiosaur, marine turtle (Danise & Higgs 2015) and bird bones (Kiel et al 2012). The one species that produces bone-eating males, O. priapus, appears to colonize smaller more ephemeral bones .…”