Mieridduryn
Mieridduryn is a genus of dinocaridid that lived during the Middle Ordovician of what is now the United Kingdom. This animal was described in 2022 based on a singular fossil found in Castle Bank, a Burgess shale type lagerstätte located in the country of Wales. Mierridduryn's affinities are somewhat uncertain, with two opinions currently being favored.
Taxonomy and research history
The genus name is a composite of two Welsh words; mieri and duryn, which means "bramble snout". The species name bonniae is named after Bonnie Douel, the fossil site owners' niece; the family heavily supported the research on the site after the discovery of the biota.The one specimen confirmed to be of this species, the holotype found in Castle Bank, was described in 2022. Initially, the focus of studies on this site was on the fossils of sponges, but later studies started to focus on the preserved arthropod fauna. The fossil was collected from a quarry on private land near Llandrindod Wells; the specific quarry is a part of the larger Gilwern Volcanic Formation, and the graptolites found dated the site to the Darriwilian of the Middle Ordovician.
This animal's taxonomic affinities are somewhat unclear; one opinion is that this animal represents a new grade of stem-euarthropods that evolved features similar to the Cambrian aged opabiniids ; another is the features seen in Mieridduryn are the result of convergent evolution, not being homologous to those seen in radiodonts; this animal would then represent a late surviving opabiniid, extending the family's range by 40 million years.
Description
This animal shares a lot of features that are characteristic of dinocaridids. The specimen measures around in length along the dorsal margin of the fossil. The head of the creature bore a fused proboscis that had slender spines on the dorsal surface, and could have also possessed a claw-like appendage. On the top of the head was a circular shaped dorsal sclerite. The mouth of this animal, known as an oral cone, was 0.4 mm in length, and preserved several lightly sclerotized plates. The trunk region had two types of appendages, being lobopod-like limbs along with dorsolateral flaps, which are significant as they thought to be exclusive to opabiniids and radiodonts, which helped support the naming of this creature as a new genus.Another fossil arthropod specimen known from Castle Bank resembles Mieridduryn and the opabiniids. This animal is far smaller than Mieridduryn, and has a slightly different anatomy. This animal was not named in the 2022 paper due to the enigmatic qualities of the specimen. It is thought that specimen may represent the larval stage of Mieridduryn due to the certain qualities that resemble the larval stage of other arthropods. It was also suggested, however that this specimen represents an entirely distinct genus and species due to its unique appearance.