The fossil shows that the creature carried small pouches tethered to its body like kites, researchers said. The study is published in the Proceedings of the National Academy of Sciences.
The ancient creature, scientifically named Aquilonifer spinosus, lived about 430 million years ago (Silurian period) on the sea floor with a variety of other animals including sponges, brachiopods, worms, snails and other mollusks, a sea spider, a horseshoe crab, various shrimp-like creatures, and a sea star.
Its genus name comes from ‘aquila,’ which means eagle or kite, and the suffix ‘fer,’ which means carry.
According to the team, led by Prof. Derek Briggs of Yale University and the Yale Peabody Museum of Natural History, Aquilonifer spinosus grew to less than half an inch long (about one cm), and there is only one known fossil of the animal, found in Herefordshire, England.
Ten juveniles of different stages of development were found attached to it with thin, flexible threads. The unusual parenting method is the only known example of its kind.
The discovery was reported April 4, 2016 in the Proceedings of the National Academy of Sciences.
According to the scientists, Aquilonifer spinosus is a member of the arthropods, the large group of animals that includes insects, spiders and crustaceans.
Many arthropods adopt different strategies to protect their young from predators, including attaching them to their limbs, holding them under their shell, or enclosing them within a special pouch until they are old enough to be released.
“Modern crustaceans employ a variety of strategies to protect their eggs and embryos from predators — attaching them to the limbs, holding them under the carapace, or enclosing them within a special pouch until they are old enough to be released — but this example is unique,” Prof. Briggs said.
“Nothing is known today that attaches the young by threads to its upper surface.”
The adult Aquilonifer spinosus postponed molting until the juveniles were old enough to hatch; otherwise, the juveniles would have been cast aside with the shed exoskeleton. The adult’s head is eyeless and covered by a shield-like structure.
“We considered the possibility that the juveniles were parasites feeding off a host, but decided it was unlikely because the attachment position would not be favorable for accessing nutrients,” Prof. Briggs said.
“This newly discovered strategy may have provided some benefits for the animal,” said co-author Dr. Mark Sutton, from Imperial College London.
“It could offer protection – the adult could have tried to fend off anything that wanted to eat the young, or carried them away from danger.”
“The adult could also have moved the young to areas where they could access a better food supply. They were probably filter-feeders, extracting nutrient-particles from the water, so perhaps the adult could orient itself to any water currents to help with this.”