An artist’s reconstruction of the tube-like animals attached to the dead phragmocone..Credit…Franz Anthony

The New York Times Trilobites column has a story about some very old ocean floor communities.  Research published recently in the journal Communications Biology looked at a 480-million-year-old cephalopod from Morocco that was posthumously converted into a condominium.  It’s the earliest known example of the recycling of biological material on the ocean floor.

The fossil arrived at Harvard in 2019, amid a collection of legally imported invertebrate fossils from the Fezouata Shale, a formation full of exquisitely preserved Ordovician fossils from the Atlas Mountains of Morocco.

The community of animals represents a transitionary period, said Karma Nanglu, a paleontologist at the Harvard Museum of Comparative Zoology and an author on the study. Preserved in the rocks are leftovers from the strange communities of the Cambrian era — full of trilobites and strange, free-swimming arthropods called radiodonts — and new arrivals from the Ordovician, when animal groups like mollusks moved high into the water column and grew significantly in size.

One of those mollusks, a straight-shelled nautiloid, died and drifted to the seafloor. By the time it was eventually covered by silt, the 1.5-inch shell had collected a tight tangle of 88 tubes, resembling a forest of little chimneys. These were the remnants of a colony of minuscule filter-feeders called pterobranchs, which use their feathery arms to pluck plankton out of the water column — and prefer to build on bits of dead animal.