This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: For more than 170 years, paleontologists have been trying to solve the mystery of what created the strangely uniform hexagonal tunnels found in fossils. In a new study published in Earth Science Reviews, a team of researchers pored over the evidence and concluded that the most likely culprit was a type of arthropod—probably a small crustacean.
This challenges a long-standing idea that a worm-like creature may have created the tunnels. The mysterious fossil pattern is referred to as "paleodictyon," and it has been discovered in marine rocks dating to the early Cambrian, more than 500 million years ago. The fossil is widespread, occurring in many areas around the world and at varying sea depths.
The creators of these oddly uniform structures have never been observed or fossilized within the tunnels, but whatever is causing them has not stopped. Scientists are still seeing fresh paleodictyon structures in the modern deep sea. The tunnels are composed of a horizontal network of hexagonal meshes and vertical outlets, measuring from a few millimeters to less than 1 millimeter in diameter.
Researchers know the animal is quite small and that the structure is probably a type of burrow system, but they do not know which animal made it. Various proposals have included worms, single-celled organisms, sponges and crustaceans. The authors of the new study say speculation about paleodictyon may go as far back as Leonardo da Vinci's time.
They write, "It is thought that Leonardo da Vinci might have been among the first to examine it, as evidenced by a drawing attributed to him that potentially illustrates paleodictyon. "As a pioneering figure in ichnology, da Vinci introduced the idea of trace fossils as the product of the activities of worm-like organisms. However, whether he specifically applied this interpretation to paleodictyon remains uncertain.
The hypothesis that paleodictyon represents a fossil burrow produced by such worm-like organisms gained considerable support during the 1970s and remains a well-established hypothesis today." The team involved in the new study does not think worms were likely capable of producing paleodictyon. Instead, its examination of fossil specimens from across Italy, Portugal and Poland, spanning from the Cambrian to more recent geological periods, suggests that the builders were a type of arthropod—a group of animals with segmented bodies, hard outer shells and jointed legs that includes crustaceans, bugs, spiders and centipedes. The team used high-resolution photography and 3D models to measure the geometry of the fossil tunnel networks and compared them with burrows made by living arthropods.
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