''Mieridduryn'' is a genus of extinct dinocaridid

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

that lived during the

Middle Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. The ...

of what is now the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...

. This animal was described in 2022 based on a singular fossil found in Castle Bank, a Burgess shale type

lagerstätte A Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues. These for ...

located in the country of

Wales Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...

. This animal's taxonomic affinities are somewhat unclear, but there are some hypotheses. One is that this animal represents a new

grade Grade most commonly refers to: * Grade (education), a measurement of a student's performance * Grade, the number of the year a student has reached in a given educational stage * Grade (slope), the steepness of a slope Grade or grading may also ref ...

Stem Stem or STEM may refer to: Plant structures * Plant stem, a plant's aboveground axis, made of vascular tissue, off which leaves and flowers hang * Stipe (botany), a stalk to support some other structure * Stipe (mycology), the stem of a mushro ...

euarthropods Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chitin, o ...

that evolved features similar to the

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

aged opabiniids (a family of basal arthropods). Another is that if the features seen in ''Mieridduryn'' are convergent, and not homologous, to those seen in

radiodonts Radiodonta is an extinct order of stem-group arthropods that was successful worldwide during the Cambrian period. They may be referred to as radiodonts, radiodontans, radiodontids, anomalocarids, or anomalocaridids, although the last two origi ...

, then this animal represents a late surviving opabiniid (if the latter option is correct, then this means the opabiniids survived for over 40 million years longer than what was once thought). Free abstract at

History of research and etymology

The one specimen of this species was found in Castle Bank, and was described in 2022. Originally, the main studies on this site focused on the

Sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...

fossils, but later on more studies started to focus on the arthropod section of the fauna. The fossil was collected from a

quarry A quarry is a type of open-pit mine in which dimension stone, rock, construction aggregate, riprap, sand, gravel, or slate is excavated from the ground. The operation of quarries is regulated in some jurisdictions to reduce their envi ...

in private land near

Llandrindod Wells Llandrindod Wells (, ; cy, Llandrindod, /ɬanˈdɾindɔd/ "Trinity Parish"), sometimes known colloquially as Llandod, is a town and community in Powys, within the historic boundaries of Radnorshire, Wales. It serves as the seat of Powys ...

. The specific quarry is a part of the larger Gilwern Volcanic Formation, and the

graptolites Graptolites are a group of colonial animals, members of the subclass Graptolithina within the class Pterobranchia. These filter-feeding organisms are known chiefly from fossils found from the Middle Cambrian (Miaolingian, Wuliuan) through the L ...

found dated the site to the

Darriwilian The Darriwilian is the upper stage of the Middle Ordovician. It is preceded by the Dapingian and succeeded by the Upper Ordovician Sandbian Stage. The lower boundary of the Darriwilian is defined as the first appearance of the graptolite species '' ...

of the Middle Ordovician. The sections of the genus name, ''mieri'' and ''duryn'' in Welsh means "Bramble snout". The species name ''Bonniae'' is named after Bonnie Douel, the niece of the owners of the site. The family heavily supported the research on the site after the discovery of the biota.

Description

This animal shares a lot of features that are characteristic of dinocaridids (including tetraradial mouthparts, flapping trunk appendages, and

lobopod The lobopodians, members of the informal group Lobopodia (from the Greek, meaning "blunt feet"), or the formally erected phylum Lobopoda Cavalier-Smith (1998), are panarthropods with stubby legs called lobopods, a term which may also be used as ...

like legs). The specimen measures around 13 mm in length on the dorsal margin of the fossil. The head of the creature bore a fused

proboscis A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular mouthparts used for feeding and sucking. In vertebrates, a proboscis is an elong ...

that had slender spines coming off the top, and could have also possessed a claw-like appendage. On the top of the head was a circular shaped dorsal

sclerite A sclerite (Greek , ', meaning "hard") is a hardened body part. In various branches of biology the term is applied to various structures, but not as a rule to vertebrate anatomical features such as bones and teeth. Instead it refers most commonly ...

(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, these being lobopod-like limbs and dorsolateral flaps. These features are important as they were at first only known from opabiniids and radiodonts, which helped support the naming of this creature as a new

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

Classification

Two main classifications were done on this creature, and the two found different results. One study found that this animal forms a

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

group with radiodonts and the deuteropods. The other, best supported study instead found this animal to be a late surviving opabiniid. The true classification of this animal however is still being debated. This does show though that the overall morphology of the opabiniids was around far longer than what was once thought.

Significance

Before this creatures discovery, it was thought that

hurdiid Hurdiidae is an extinct cosmopolitan family of radiodonts, a group of stem-group arthropods, which lived during the Paleozoic Era. It is the most long-lived radiodont clade, lasting from the Cambrian period to the Devonian period. Descripti ...

radiodonts (like ''

Aegirocassis ''Aegirocassis'' is an extinct genus of radiodont arthropod belonging to the family Hurdiidae that lived 480 million years ago during the early Ordovician. It is known by a single species, ''Aegirocassis benmoulai''. Van Roy initiated scientifi ...

'', '' 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. There is actually another fossil arthropod (NMW.2021.3 G.8) known from castle bank that 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 A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The l ...

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 In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

due to its unique appearance.

References

{{Taxonbar, from=Q115378427 Dinocarida Prehistoric arthropod genera Fossil taxa described in 2022