Etched on seafloors around the world is an enigmatic honeycomb pattern, the source of which has eluded explanation for centuries. It shows up on 520-million-year-old Cambrian ocean sediments in Portugal as well as in modern oceans.
Confusion about the origins of the hexagonal networks—dubbed Paleodictyon—began as early as the mid-18th century, with some geologists speculating that the marks were from physical and chemical changes to hardening sediments, while others attributed them to algae or tadpoles. Italian geologist Giuseppe Scarabelli even proposed the idea that they were fossilized beehives.
A recent study published in the journal Earth-Science Reviews, however, identified a totally different, much more plausible culprit: a small burrowing arthropod, something like an isopod or amphipod with a flattened, segmented body.
Andrea Baucon, a paleontologist at the University of Cagliari in Italy, and her coauthors in Poland and Portugal examined Paleodictyon patterns from multiple locales spanning 530 million years to describe the geometry of the traces. They found that within a single hexagonal cell, the six sides differed by just half a millimeter on average, forming a regular shape. Each hexagon appeared to be the entrance to a straight tunnel with sharp corners, which was strong evidence that the builder was an arthropod.
Marine arthropods are known for making clean angles on their burrows, thanks to their anatomy that allows for sharp changes in direction. (The study authors also noted that the appearance of Paleodictyon in the early Cambrian coincided with the earliest known fossils of arthropods.) “That is how arthropods dig, scraping the sediment with jointed legs, supported by a rigid exoskeleton,” said study author Alfred Uchman from the Institute of Geological Sciences in Poland.
But why would these crustaceans build a network of abutting hexagons?
A prior working hypothesis was that the burrows were for bacteria farming, such as by lugworms. But the study authors proposed something novel—that “the hexagonal mesh is actually … a communication network for a colony,” since it’s got the right shape for transmission of signals in all directions, robustness, local clustering, and scalability. The signals may have been acoustic, chemical, or even hydraulic-based on moving water.
If they’re right, that would make Paleodictyon both a geometric and a communication marvel. 
Enjoying Nautilus? Subscribe to our free newsletter.
Lead Image & Videos Credit: Natural History Museum of Piacenza
