A new species of megacheiran arthropod from the Ordovician period, preserved in 3D by pyrite (commonly known as fool’s gold), has been discovered by University of Oxford paleontologist Luke Parry and his colleagues.
Life reconstruction of Lomankus edgecombei. Image credit: Xiaodong Wang.
Lomankus edgecombei lived in the Ordovician seas approximately 450 million years ago.
The fossil was found at a paleontological site in New York State, the United States, that contains the famous Beecher’s Trilobite Bed.
Aside from trilobites, other kinds of organisms are much less common at the site, reflecting the rarity of this find.
“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,” said Yale University’s Professor Derek Briggs.
Lomankus edgecombei belongs to Megacheira, an iconic group of arthropods with a large, modified leg at the front of their bodies that was used to capture prey.
Megacheirans 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).
The discovery of Lomankus edgecombei offers important new clues towards solving the long-standing riddle of how arthropods evolved the appendages on their heads: one or more pairs of legs at the front of their bodies modified for specialised functions like 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,” Dr. Parry said.
“Part of the key to this success is their highly adaptable head and its appendages, that has adapted to various challenges like a biological Swiss army knife.”
The holotype specimen of Lomankus edgecombei: photograph at left, other images are 3D models from CT scanning. Image credit: Luke Parry / Yu Liu / Ruixin Ran.
While other megacheirans used their large first appendage for capturing prey, in Lomankus edgecombei the typical claws are much reduced, with three long and flexible whip-like flagella at their end.
This suggests that the new species was using this frontal appendage to sense the environment, rather than to capture prey, indicating it lived a very different lifestyle to its more ancient relatives in the Cambrian period.
Unlike other megacheirans, Lomankus edgecombei 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.
“Rather than representing a ‘dead end’, Lomankus edgecombei shows us that megacheirans continued to diversify and evolve long after the Cambrian, with the formerly fearsome great appendage now performing a totally different function,” Dr. Parry said.
The fossil offers new clues towards solving the highly-debated question of what the equivalent of the great appendage of megacheirans is in living species.
“These beautiful new fossils show a very clear plate on the underside of the head, associated with the mouth and flanked by the great appendages,” said Yunnan University’s Professor Yu Liu.
“This is a very similar arrangement to the head of megacheirans from the early Cambrian of China except for the lack of eyes, suggesting that Lomankus edgecombei probably lived in a deeper and darker niche than its Cambrian relatives.”
“This arrangement of features on the head is similar to living arthropods, suggesting the great appendage is the equivalent of the antenna of insects and the chelicera (mouthparts) of spiders and scorpions.”
The discovery is reported in a paper in the journal Current Biology.
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Luke Parry et al. A pyritised Ordovician leanchoiliid arthropod. Current Biology, in press; doi: 10.1016/j.cub.2024.10.013