'Gold-plated' prehistoric arthropod discovery – 450-million-year-old prehistoric arthropod 'Lomankus edgecombei' poses a mystery

Golden Arthropods: Paleontologists in New York State have discovered a shimmering golden fossil of a previously unknown prehistoric arthropod. This relic gets its unusual shine from the mineral pyrite – also known as fool's gold. Lomankus edgecombei lived 450 million years ago on the oxygen-poor seafloor and was no bigger than a little finger. The animal also had no eyes, and had some other unusual features.

During the Cambrian Period, 538 to 485 million years ago, most life occurred in the oceans. Among the most fearsome predators were aquatic arthropods such as the one-metre-long Anomalocaris or members of the so-called Megacheira – “big hands” in German. These armored predators once hunted their prey with scissor-like head appendages. But according to paleontologists, their appearance on the scene of life did not last long. In the Ordovician, 485 to 443 million years ago, Megashira may have already been largely extinct.

Arthropods without scissors or eyes

In New York State, paleontologists led by Luke Parry of the University of Oxford have found a new member of the rare Ordovician species Megashira. The arthropod, called Lomankus edgecombei, was only a few centimeters long and swam in the Ordovician seas 450 million years ago. He and his fossil remains have some special features that distinguish him from other members of Megacheira.

For example, Lomancus' head appendages are not claw-like grippers, but rather whip-like flagella, Barry and colleagues reported. These pests were probably not suitable for catching prey, but were probably used to improve perception of the environment. The tiny arthropods were in desperate need of this sensory support because they did not have eyes and probably lived in dark, oxygen-poor areas of the Ordovician Sea, the team suspects.

Fool's gold as a trump card

Thanks to this oxygen-poor habitat, the delicate features of Lomancus have been preserved to this day. After the arthropods died out 450 million years ago and were buried by sediments, a special form of mineralization began due to these anoxic conditions: parts of the organic matter were replaced by the mineral pyrite (FeS).₂) replacing.

Also known as fool's gold, it is an iron sulfide mineral that gives fossils a golden glow and can reveal hidden details of their anatomy. Due to its high density, it allows, for example, detailed CT scans, on the basis of which the fossil can be reconstructed in three dimensions.

News about the evolution of arthropods

In the case of Lomancus, thanks to pyrite, Barry and his team discovered, among other things, the thread-like “arms” of arthropods, which now reveal more about the evolutionary history of Megashira. “Lomancus is not a dead end, but it does show us that Megashyra continued to diversify and evolve long after the Cambrian, with the previously large, fearsome appendage now serving a very different function,” Barry explains.

At the same time, Lomancus's unusual head appendages suggest that both these appendages and earlier Megashira clutches were equivalent to the insect antennae or mouthparts of spiders and scorpions, Barry and colleagues reported. (Current Biology, 2024; doi: 10.1016/j.cub.2024.10.013)

Source: Oxford University

October 30, 2024 – Anna Manz