As any parent knows, keeping tabs on your developing young in a dangerous world can be a trial. A tiny, resourceful creature that lived 430 million years ago devised a novel method for such baby tracking: It tethered egg pouches to its back with threads and trailed its juveniles as they grew, as if they were tiny kites.
Scientists recently described the arthropod — a type of invertebrate with a segmented body and exoskeleton — and its unusual parenting practice in a new study, with the animal's kitelike appendages inspiring them to name the specimen after "The Kite Runner," a popular 2003 novel by Khaled Hosseini.
The first part of its scientific name, Aquilonifer spinosus, is derived from the Latin words aquila (eagle or kite) and fer (carry). [Video: Ancient 'Kite Runner' Creature Flew Its Young on Strings]
"Like Pompeii on the ocean floor"
Eyeless, flat-bodied A. spinosus measured less than 0.5 inches (1.3 centimeters) long. A shield protected its head, which was topped by two sweeping antennalike structures, and it used its 12 pairs of legs to scuttle across the sea bottom in what is now Herefordshire in the U.K. The region looks very different today — for one, it's not underwater anymore — but fossils of numerous small creatures like A. spinosus that once inhabited the ocean are preserved in outcrops inside rocky spheres, "like baseballs," of hardened volcanic ash called concretions, which formed around their remains, said Derek Briggs, a paleontology professor at Yale University and lead author of the study.
"The tendency is to think of this as Pompeii on the ocean floor," Briggs said.
Typically, each concretion holds a single fossil, which is usually too small to be chipped out of the rock. Scanning methods that typically help paleontologists reconstruct embedded fossils aren't much use for these specimens, he said, because their mineral composition is too similar to the concretion around them for the scans to distinguish between the two.
Destroying to preserve
So Briggs turned to the only surefire way to study these tiny fossils in three dimensions: He and his colleagues split open each concretion and cut out the rock holding the fossil. Then, they ground away slices of the embedded specimen, each just microns (millionths of a meter) thick, and photographed each to rebuild the fossil as a digital model — a process that took many hours.
Though grinding destroys the original specimen, the results are worth it because they yield a highly detailed model that can be studied from any angle and can be reproduced multiple times, Briggs said.
And what Briggs and his colleagues found when they reconstructed their "Kite Runner" was something they had never seen before: an arthropod trailing strings attached to 10 flattened pods that appeared to contain juveniles.
In the false-color digital reconstruction, the little legs of the baby kite runners could be seen as traces of bright green in and immediately around the pods. The scientists counted approximately six limbs on the juveniles — half as many legs as the adult form, perhaps because the young were still developing, Briggs said.
Though it's possible that these pods contained hitchhikers or parasites, it's less likely, Briggs added. A. spinosus had long, antennalike structures on its head that could have been used to sweep away pesky stowaways, he proposed. And the threads were tethered to body spines — an inefficient feeding path for a parasite, which typically prefers to latch on close to the host's body.
This unique discovery suggests that arthropods during this period were still experimenting with methods of brooding their young. In fact, some of these approaches — like carrying young directly on their backs — are used by species alive today, though this particular "kite" method is not.
And according to Briggs, there are likely many more fossil surprises tucked away in numerous concrete spheres from this site that are yet to be discovered.
"Many of these things are unique; it's the only place they're found in the fossil record," he said. "They tend, for that reason, to reveal details about particular groups and how they evolved that are just not available anywhere else."
The findings were published online today (April 4) in the journal Proceedings of the National Academy of Sciences.