The most renowned remains first from the Cambrian explosion on animal life almost half a billion years ago differ sharply from their current equivalents. These "strange wonders," like the five-eyed Opabinia with its unusual frontal proboscis and the terrifying alpha predator Anomalocaris including its radial mouthparts and spiky eating tentacles, have become cultural icons.
However, they were only recently identified as extinct evolutionary phases critical to understanding the origins of one of the largest and most significant living organisms, the arthropods, which are defined as a group that comprises modern crabs, arachnids, spiders, and millipedes. A report published lately in the journal Nature Communications describes two new taxa with a strong resemblance to Opabinia. They were recognized in a new fossil layer from the Ordovician Period, 40 million years after the Cambrian boom.
This deposit was found during the COVID-19 lockdowns in a sheep pasture in Llandrindod Wells in central Wales (UK) by independent researchers, including Llandrindod locals Dr. Joseph Botting Dr. Lucy Muir, Honorary Research Scholars at Amgueddfa Cymru - National Museum Wales.
Cambrian Explosion: Biological Big Bang
The Cambrian explosion, often known as the biological great bang, refers to a time in the Cambrian Period approximately 530 million years ago when almost all mammals and birds' phyla started appearing in the fossil record.
The mine is well recognized as one of the numerous nearby locations where rare species of fossilized sponges have been discovered. When the lockdown began, the team planned to make one more trip to collect some more sponges before finally writing them up, but that was the day they discovered something poking its tentacles out of a tube instead.
This is what paleontologists dream about, true delicate preservation, said Muir. That was the start of a comprehensive and ongoing inquiry that expanded into international cooperation, with primary author Dr. Stephen Pates (University of Cambridge) with senior author Dr. Joanna Wolfe (University of Cambridge) (The Department of Organismic and Evolutionary Biology at Harvard University).
Among the fossils discovered thus far are two extremely unexpected Cambrian "strange marvels." Pates gathered with Botting as well as Muir to investigate the samples using microscopes obtained through crowd-funding. The bigger specimen was 13 mm (0.5 inches) in length, while the smaller one was only 3 mm in length (0.12 inches). Opabinia specimens can grow to be 20 times as long).
As described by the scientists, during this visit, extensive research uncovered new features in the new material. Some of these characteristics are also seen in Opabinia, including triangular, squishy lobopod 'legs' for engaging with the sediment and a tail fan with blades comparable in form to Opabinia's recently identified sibling, Utaurora.
History of Arthropod Evolution
From the conclusion of the Cambrian Period 485.4 million years ago (Mya) to the commencement of the Silurian Period 443.8 Mya, the Ordovician period covers 41.6 million years. Mieridduryn bonniae is a new taxon described by the authors, with the bigger specimen assigned as the holotype. The smaller specimen's status was left open to represent these several possibilities. The genus term Mieridduryn is taken from the Welsh language and translates as "bramble-snout," describing the new material's spiky proboscis. It sounds like "me-airy-theerin."
To assess their location in the history of arthropod evolution, the researchers performed phylogenetic studies to compare the new fossils to 57 other extant and ancient arthropods, radiodonts, and panarthropoda.
These findings revealed that a proboscis-a fused set of head appendages thought to be exclusive to opabiniids-was included in the lineage of radiodonts to deuteropods (more derived, contemporary arthropods) and may have evolved to develop into the labrum that surrounds the mouth in current arthropods. Nevertheless, the second-best-supported classification for such specimens was real opabiniids; thus, the authors inquired further to evaluate the durability of this first conclusion.
If some or all of the traits shared by the Welsh creatures and radiodonts were thought to have developed convergently, the results strongly suggested that these individuals were authentic opabiniids, first from beyond North America and also the latest by 40 million years.
But whatever the outcome, the fossils represent a significant new component in the puzzle of arthropod evolution. These little yet scientifically significant fossils are among the first discoveries from the Ordovician fauna. Botting and Muir's work in the little cave in the sheep pasture continues, with more to come.
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