This ‘Kite Runner’ arthopod kept its young tethered to its body with strings

Modern-day parents aren’t the first to put their kids on a leash. This week researchers describe an unusual 430-million-year-old arthropod that appears to have kept its young tethered to its body with strings in order to keep them safe.

Arthropods are a diverse group of animals that include crustaceans, millipedes, centipedes and insects. This particular specimen, which represents a very early branch in the group’s evolutionary line, was less than half an inch long, blind and crawled along the bottom of an ancient sea floor. Its 10 offspring were encased in tiny capsules and attached by threads to the back of its body.

It was discovered in the Herefordshire Lagerstätte -- or volcano deposit -- in the west midlands of England.

The research team that discovered the animal named it Aquilonifer spinosus, which translates roughly to “spiny kite bearer.” That’s because the scientists thought the 10 small, flattened and lemon-shaped capsules that contained the arthropod’s babies must have looked like kites as they trailed in the water behind their parent.

In a paper describing Aquilonifer spinosus published Monday in the Proceedings of the National Academy of Sciences of the United States of America, the authors note that they also wanted to pay homage to the 2003 novel “The Kite Runner” by Khaled Hosseini.

Although arthropods have been known to protect their young, Derek Briggs, curator of invertebrate paleontology at the Yale Peabody Museum of Natural History and the first author on the paper, said this is the first time anyone had seen an arthropod use this particular brooding strategy.

“This is the only occurrence of this kind of behavior known among fossil or living arthropods,” he said in an email to the Los Angeles Times. “Juveniles are tethered to the limbs of some living freshwater crayfish during their development, but attachment to the back of an arthropod, in this case, is unique.”

To be sure that the 10 kite-like capsules attached to the Aquilonifer‘s back were indeed juveniles, Briggs and his co-authors on the paper first had to rule out the possibility that they might be parasites or some other animal just hitching a ride.

They explain that both the size and the number of limbs belonging to the animals inside the sacs are strongly consistent with them being juvenile versions of the adult. Also, their attachment strings are too thin and too long to make sense as a way for parasites to draw nutrients from a host.

Finally, they conclude that they couldn’t be hitching a ride, because the adult would not have tolerated the drag they generate. Its long front appendages would have been long enough to snap the strings.

The juvenile hypothesis, however, seems to make perfect sense.

“The tethering strategy would have afforded protection from predators in the early stages of larval development by keeping them close to the adult,” Briggs said. “It would be much easier to prey on the young if they were free living.”

The researchers propose that the adult used its front appendages to transfer food it found along the sea floor to its mouth. The juveniles, however, were probably floating in the water above their parent, using their appendages to filter phyto-or zooplankton from their environment -- their small threads keeping them safely in the vicinity of mom or dad.

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