In a study published in Nature, researchers, led by postdoctoral researcher Karma Nanglu, describe a 480-million-year-old cephalod from Morocco that shows the earliest example of ocean bottom dwellers making their home in dead bodies.
Dead bodies in the ocean drift to the bottom where they become home to bottom dwellers, the practice dates back to 530 million years ago. During the Paleozoic era, however, it became much harder to track the interspecies interactions. Nanglu and co-authors, Professor Javier Ortega-Hernández, PhD candidate Jared Richards, and undergraduate Madeleine Waskom, discovered a fossil that arrived at the Museum of Comparative Zoology in 2019. The half-billion year old cephalod was part of a legally imported invertebrate fossils from the Fezouata Share, a formation containing perfectly preserved Ordovician fossils from the Atlas Mountains of Morocco. The rocks are full of trilobites, radiodonts, and new groups from the Ordovician, such as mollusks.
Nanglu noticed that one of those mollusks, a straight-shelled nautiloid that had died and drifted to the seafloor, was covered by what appeared to resemble little chimneys. The 88 tubes were actually remnants of a colony of tiny filter-feeders called pterobranchs, which use their feathery arms to pluck plankton out of the water column and build on bits of dead animals.
Pterobranchs, which Nanglu described as "really minute", were so abundant in the early Paleozoic that their fossils were used to help correlate ages of rocks, before they vanished 300 million years ago.
According to Nanglu, they've been colonizing mollusk shells for half a billion years and still do so in modern oceans. However, examples of interactions between different species are much rarer during the Ordovician period, which follows the Cambrian, making this cephalod a very important insight into ancient living ecosystems.