[ad_1]
The bodies of the dead float to the bottom of the ocean, where the bottom dwellers use them. They build temporary reefs with the bones of modern whales, and they did the same with their previous relatives and mesozoic marine reptiles.
This recycling dates back to 530 million years ago, when complex animal life first appeared in rock. However, as animal life diversified into the early Paleozoic era, the history of such species interactions became more difficult to trace.
In research published Wednesday in Communications BiologyHowever, a team of researchers describes a 480-million-year-old Moroccan cephalopod that was posthumously converted into a condominium: the oldest example of a relationship dating back almost 500 million years.
The fossil arrived at Harvard in 2019, amid a collection of invertebrate fossils legally imported from the Fezouata Shale, a formation filled with exquisitely preserved Ordovician fossils from Morocco’s Atlas Mountains.
The animal community represents a period of transition, said Karma Nanglu, a paleontologist at the Harvard Museum of Comparative Zoology and an author of the study. The rocks preserve remains of the strange communities of the Cambrian era (full of trilobites and strange free-swimming arthropods called radiodonts) and recent arrivals from the Ordovician, when groups of animals such as mollusks moved to the top of the water column. and grew significantly in size.
One of those mollusks, a straight-shelled nautiloid, died and drifted to the sea floor. When it was finally covered in slime, the 1.5-inch shell had accumulated a tight tangle of 88 tubes, resembling a forest of small chimneys. These were the remains of a colony of tiny filter feeders called pterobranchs, which use their feathery arms to extract plankton from the water column and prefer to build on pieces of dead animals.
“They’re really tiny,” Dr. Nanglu said. “This piece of cephalopod skeleton would be the equivalent of a multi-story building to a pterobranch.”
Planktonic graptolites, a branch of the family, were so abundant in the early Paleozoic period that their tiny fossils were used to help correlate the ages of rocks, before disappearing 300 million years ago. But the tube-building side of the family still lives modest lives on the seafloor, and their larvae grow on any piece of hard-shelled animal they can find.
“They have been colonizing mollusk shells for 500 million years and are still doing their thing in modern oceans,” Dr. Nanglu said. “Anything that can maintain the same lifestyle for a long time is worth paying attention to.”
Pterobranchs may have been there for an unusually long time, but evidence of animals building their homes on top of other animals has a remarkably deep fossil record. Some of the earliest examples appear 25 million years before the Fezouata specimen. In the Cambrian, tubes built by one species of giant worms housed another, and brachiopods encrusted the bodies of free-swimming arthropods, like the barnacles of modern whales.
“As soon as there are big things swimming in the water column, things are looking for free rides,” Dr. Nanglu said. “And as soon as things die, you’ll see animals building their entire lives on what is essentially a corpse. As soon as a resource is available, some animal will find a way to exploit that resource in a short time.”
But while Cambrian deposits like the Burgess Shale preserve multiple examples of interactions between different species, similar sites from the following Ordovician period are much rarer, Dr Nanglu said. Even sites like Fezouata, known for its diverse range of well-preserved invertebrates, rarely contain them. That makes the tube-encrusted cephalopod a tantalizing glimpse of a living ecosystem.
“It helps flesh out that these early animals were doing interesting things and designing ecosystems for themselves,” Dr. Nanglu said. “Sometimes we don’t see it until we have a fossil like that.”