A 450-million-year-old fossil arthropod, preserved in iron pyrite (fool’s gold), has been unveiled by scientists.
The new species Lomankus edgecombei is distantly related to spiders and scorpions and belongs to a group of arthropods called megacheirans, which had a large modified leg at the front of their bodies to capture prey. Megacheirans like Lomankus were very diverse during the Cambrian Period (538-485 million years ago) but were thought to be largely extinct by the Ordovician Period (485-443 million years ago).
Researchers led by Oxford Associate Professor Luke Parry believe this to be an important discovery because it offers new clues towards solving the riddle of how arthropods evolved the appendages on their heads.
These appendages are one or more pairs of legs at the front of their bodies, modified for sensing the environment and capturing prey. Such appendages include the antennae of insects and crustaceans, and the pincers and fangs of spiders and scorpions.
“Today, there are more species of arthropod than any other group of animals on Earth. Part of the key to this success is their highly adaptable head and its appendages, which have adapted to various challenges like a biological Swiss army knife,” Professor Parry said.
An early form of antennae
While other megacheirans used their large first appendage for capturing prey, in Lomankus the typical claws are much reduced, with three long and flexible whip-like flagella at their end. This suggests that Lomankus was using this frontal appendage to sense the environment, rather than to capture prey.
According to the research team, this indicates it lived a very different lifestyle to its more ancient relatives in the Cambrian Period. Unlike other megacheirans, Lomankus seems to lack eyes, suggesting that it relied on its frontal appendage to sense and search for food in the dark, low-oxygen environment in which it lived.
The fossil also offers new clues towards solving the highly-debated question of what the equivalent of the appendage of megacheirans is in living species. According to the study, published in the journal Current Biology, the arrangement of features on the head of Lomankusis similar to the antenna of insects and the mouth parts of spiders and scorpions.
Preserved in gold
The golden fossil was discovered at a site in New York State containing the famous ‘Beecher’s Trilobite Bed’; a layer of rock with multiple preserved trilobites.
The animals preserved in this layer lived in a low oxygen environment that allowed pyrite, commonly known as fool’s gold, to replace parts of their bodies after they were buried in sediment, resulting in spectacular golden 3D fossils.
Professor Derek Briggs, a co-author of the study at Yale University said: “These remarkable fossils show how rapid replacement of delicate anatomical features in pyrite before they decay, which is a signature feature of Beecher’s Trilobite Bed, preserves critical evidence of the evolution of life in the oceans 450 million years ago.”
Professor Parry added, “As well as having their beautiful and striking golden colour, these fossils are spectacularly preserved. They look as if they could just get up and scuttle away.”
Top image: The holotype specimen of Lomankus edgecombei. Photograph at left, other images at right are 3D models from CT scanning. Credits: Luke Parry (photograph), Yu Liu, Ruixin Ran (3D model