Mieridduryn

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 (converging with this family of basal arthropods); another is the features seen in Mieridduryn are the result of convergent evolution, not being homologous to those seen in radiodonts;{{Clarify|date=May 2025}} this animal would then represent a late surviving opabiniid, extending the family's range by 40 million years.{{cite journal |last1=Pates |first1=S. |last2=Botting |first2=J. P. |last3=Muir |first3=L. A. |last4=Wolfe |first4=J. M. |year=2022 |title=Ordovician opabiniid-like animals and the role of the proboscis in euarthropod head evolution |journal=Nature Communications |volume=13 |issue=1 |at=6969 |doi=10.1038/s41467-022-34204-w |pmid=36379946 |pmc=9666559 |doi-access=free|bibcode=2022NatCo..13.6969P }}{{Cite journal |last1=Pates |first1=Stephen |last2=Wolfe |first2=Joanna M. |last3=Lerosey-Aubril |first3=Rudy |last4=Daley |first4=Allison C. |last5=Ortega-Hernández |first5=Javier |date=2022-02-09 |title=New opabiniid diversifies the weirdest wonders of the euarthropod stem group |journal=Proceedings of the Royal Society B: Biological Sciences |volume=289 |issue=1968 |pages=20212093 |doi=10.1098/rspb.2021.2093 |pmc=8826304 |pmid=35135344}}{{Cite journal |last=Briggs |first=Derek E. G. |date=2015-04-19 |title=Extraordinary fossils reveal the nature of Cambrian life: a commentary on Whittington (1975) 'The enigmatic animal Opabinia regalis, Middle Cambrian, Burgess Shale, British Columbia' |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |volume=370 |issue=1666 |pages=20140313 |doi=10.1098/rstb.2014.0313 |pmc=4360120 |pmid=25750235|bibcode=2015RSPTB.37040313B }}{{cite journal |author=Whittington, H. B. |date=June 1975 |title=The enigmatic animal Opabinia regalis, Middle Cambrian Burgess Shale, British Columbia |journal=Philosophical Transactions of the Royal Society B |volume=271 |issue=910 |pages=1–43 271 |bibcode=1975RSPTB.271....1W |doi=10.1098/rstb.1975.0033 |jstor=2417412 |doi-access=}} Free abstract at {{cite journal |last1=Whittington |first1=H. B. |year=1975 |title=The Enigmatic Animal Opabinia regalis, Middle Cambrian, Burgess Shale, British Columbia |journal=Philosophical Transactions of the Royal Society B |volume=271 |issue=910 |pages=1–43 |bibcode=1975RSPTB.271....1W |doi=10.1098/rstb.1975.0033 |doi-access=}}

File:Mieridduryn bonniae NMW.2021.3G.7 oral cone.jpg

This animal shares a lot of features that are characteristic of dinocaridids (including tetra-radial mouthparts, flapping trunk appendages, and lobopod like legs). The specimen measures around {{Convert|13|mm}} 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 (similar to the ones seen in radiodonts). 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.{{Cite journal |last1=Ortega-Hernández |first1=Javier |last2=Janssen |first2=Ralf |last3=Budd |first3=Graham E. |date=2017-05-01 |title=Origin and evolution of the panarthropod head – A palaeobiological and developmental perspective |journal=Arthropod Structure & Development |series=Evolution of Segmentation |language=en |volume=46 |issue=3 |pages=354–379 |doi=10.1016/j.asd.2016.10.011 |issn=1467-8039 |pmid=27989966|doi-access=free |bibcode=2017ArtSD..46..354O }}{{Cite journal |last=Ortega-Hernández |first=Javier |date=2016 |title=Making sense of 'lower' and 'upper' stem-group Euarthropoda, with comments on the strict use of the name Arthropoda von Siebold, 1848 |journal=Biological Reviews |language=en |volume=91 |issue=1 |pages=255–273 |doi=10.1111/brv.12168 |issn=1469-185X |pmid=25528950 |s2cid=7751936}}

{{Multiple image

| image1 = NMW.2021.3 G.8.webp

| image2 = 20221119 NMW.2021.3 G.8 diagrammatic reconstruction.png

| caption2 = Interpretations of NMW.2021.3 G.8

| direction = vertical

}}

Another fossil arthropod specimen known from Castle Bank (NMW.2021.3 G.8) 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.

Before this species' discovery, it was thought that hurdiid radiodonts (like Aegirocassis, Pseudoangustidontus and Schinderhannes) were the only dinocaridids that survived past the Cambrian. This creature shows that dinocaridids were possibly more diverse and abundant in the post-Cambrian oceans than previously thought. If this creature proves to be an opabiniid it means these creatures survived far longer into the middle Ordovician, and did not go extinct in the Cambrian.{{Cite journal |last1=Van Roy |first1=Peter |last2=Briggs |first2=Derek E. G. |date=2011 |title=A giant Ordovician anomalocaridid |url=https://www.nature.com/articles/nature09920 |journal=Nature |language=en |volume=473 |issue=7348 |pages=510–513 |doi=10.1038/nature09920 |pmid=21614078 |bibcode=2011Natur.473..510V |s2cid=205224390 |issn=1476-4687|url-access=subscription }}{{cite journal |author=Gabriele Kühl |author2=Derek E. G. Briggs |author3=Jes Rust |name-list-style=amp |year=2009 |title=A great-appendage arthropod with a radial mouth from the Lower Devonian Hunsrück Slate, Germany |journal=Science |volume=323 |issue=5915 |pages=771–773 |bibcode=2009Sci...323..771K |doi=10.1126/science.1166586 |pmid=19197061|s2cid=47555807 }}

Two main classifications were done on this creature, and the two found different results. One study found that this animal forms a monophyletic group with radiodonts and the deuteropods.{{Citation needed|date=May 2025|reason=Which study?}} The other, better supported study instead found this animal to be a late surviving opabiniid. The true classification of this animal however is still being debated, though this taxon does show that the opabiniid bauplan was around far longer than what was originally thought.

{{clade|Pambdelurion|{{clade

|1=Opabiniidae

|2={{clade

|1=Mieridduryn

|2={{clade

|1=Radiodonta

|2=Deuteropoda }} }} }}}}

{{Reflist}}

{{Dinocaridida}}

{{Taxonbar|from=Q115378427}}

Category:Dinocaridida

Category:Prehistoric arthropod genera

Category:Fossil taxa described in 2022