''Willwerathia'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of Devonian

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

. It is sometimes classified as

synziphosurine Synziphosurina is a paraphyletic group of chelicerate arthropods previously thought to be basal horseshoe crabs (Xiphosura). It was later identified as a grade composed of various basal euchelicerates, eventually excluded from the monophyletic Xi ...

, a

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

group of

horseshoe crab Horseshoe crabs are arthropods of the family Limulidae and the only surviving xiphosurans. Despite their name, they are not true crabs or even crustaceans; they are chelicerates, more closely related to arachnids like spiders, ticks, and scor ...

-like

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

chelicerate The subphylum Chelicerata (from Neo-Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. Chelicerates include the sea spiders, horseshoe crabs, and arachnids (including harvestmen, scorpions, spiders, solifuges, ticks ...

arthropods, while some studies compare its morphology to an

artiopod Artiopoda is a clade of extinct arthropods that includes trilobites and their close relatives. It was erected by Hou and Bergström in 1997 to encompass a wide diversity of arthropods that would traditionally have been assigned to the Trilobitomor ...

. ''Willwerathia'' known only by one

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

, ''Willwerathia laticeps'', discovered in

deposits A deposit account is a bank account maintained by a financial institution in which a customer can deposit and withdraw money. Deposit accounts can be savings accounts, current accounts or any of several other types of accounts explained below. ...

of the

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...

from the

Klerf Formation The Klerf Formation is an Early Devonian (Emsian) formation that includes a Lagerstätte in the Northern Eifel hills, at Willwerath near Prüm, Rhineland-Palatinate, Germany. In it ''Jaekelopterus rhenaniae'', a giant eurypterid was discovered. ...

, in the

Rhenish Slate Mountains The Rhenish Massif, Rhine Massif or Rhenish Uplands (, : 'Rhenish Slate Uplands') is a geologic massif in western Germany, eastern Belgium, Luxembourg and northeastern France. It is drained centrally, south to north by the river Rhine and a few ...

Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...

Morphology

20200929 Synziphosurina Synziphosurine size comparison

As a

, ''Willwerathia'' is unusually large and so far the largest known synziphosurine, with largest

carapace A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the unde ...

measured about 90mm in width.

Prosoma The cephalothorax, also called prosoma in some groups, is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. (The terms ''prosoma'' and ''opisthosoma'' are equivalent to ''cepha ...

of ''Willwerathia'' covered by a vaulted carapace with pointed genal spines, recurved (M-shaped) ophthalmic ridges and pairs of dorsal nodes.

Tergite A ''tergum'' (Latin for "the back"; : ''terga'', associated adjective tergal) is the Anatomical terms of location#Dorsal and ventral, dorsal ('upper') portion of an arthropod segment other than the head. The Anatomical terms of location#Anterior ...

s of the

opisthosoma The opisthosoma is the posterior part of the body in some arthropods, behind the prosoma ( cephalothorax). It is a distinctive feature of the subphylum Chelicerata (arachnids, horseshoe crabs and others). Although it is similar in most respects ...

are either incomplete or disarticulated in available

materials, making it difficult to reveal the original number of opisthosomal segments. The opisthosoma of ''Willwerathia'' most likely compose of 10 segments, each expressed by a tergite that bore a median dorsal spine and a pair of tergopleurae (lateral extensions). The opisthosoma subdivided into a wider, most likely 7-segmented preabdomen and a narrower, 3-segmented postabdomen. tergite of the first opisthosomal segment is reduced in length while the remaining segments possess well-developed tergites with lateral nodes and posteriorly curved tergopleurae. The final segment terminated with a short, teardrop-shaped

telson The telson () is the hindmost division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment (biology), segment of the arthropod body, or an additional division that is not a true segm ...

Paleoecology

''Willwerathia'' was most likely a bottom-dwelling

predator Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

. The marked articulation surfaces on each of the preabdominal segments suggest that ''Willwerathia'' capable to enroll itself in a way similar to ''

Legrandella ''Legrandella'' is a genus of synziphosurine, a paraphyletic group of fossil chelicerate arthropods. ''Legrandella'' was regarded as part of the clade Prosomapoda. Fossils of the single and type species, ''L. lombardii'', have been discovered in ...

''. The environment in which ''Wilwerathia'' lived in was likely an

estuarine An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

deltaic A river delta is a landform, archetypically triangular, created by the deposition of the sediments that are carried by the waters of a river, where the river merges with a body of slow-moving water or with a body of stagnant water. The creati ...

one, and other animals like the largest

eurypterid Eurypterids, often informally called sea scorpions, are a group of extinct marine arthropods that form the Order (biology), order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period, 467.3 Myr, mil ...

, ''

Jaekelopterus ''Jaekelopterus'' is a genus of predatory eurypterid Eurypterids, often informally called sea scorpions, are a group of extinct marine arthropods that form the Order (biology), order Eurypterida. The earliest known eurypterids date to the ...

'', are known from the same formation.

Classification

''Willwerathia'' was originally thought to be an

(sea scorpion), with additional fossils described in 1998 reveal its

affinities. In the redescription done by Anderson et al. 1998, ''Willwerathia'' had been grouped under the synziphosurine

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Weinberginidae alongside ''

Weinbergina ''Weinbergina'' is a genus of synziphosurine, a paraphyletic group of fossil chelicerate arthropods. Fossils of the single and type species, ''W. opitzi'', have been discovered in deposits of the Devonian period in the Hunsrück Slate, Germany ...

'' and ''

'', a classification which is not supported by

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

analysis. ''Willwerathia'' was regarded as part of the

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

Xiphosura Xiphosura (; , in reference to its sword-like telson) is an order of arthropods related to arachnids. They are more commonly known as horseshoe crabs (a name applied more specifically to the only extant family, Horseshoe crab, Limulidae). They fir ...

''sensu stricto'' (true horseshoe crab) by Lamsdell 2013, but further phylogenetic analysis repeatedly resolving it within a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

compose of Bunodids, Pseudoniscids and

Dekatriata Dekatriata is a clade of planatergan chelicerates including the groups Arachnida, Chasmataspidida, Eurypterid Eurypterids, often informally called sea scorpions, are a group of extinct marine arthropods that form the Order (biology), order E ...

n (

chasmataspidid Chasmataspidids, sometime referred to as chasmataspids, are a group of extinct chelicerate arthropods that form the Order (biology), order Chasmataspidida. Chasmataspidids are probably related to horseshoe crabs (Xiphosura) and/or sea scorpions (E ...

s, eurypterids and

arachnid Arachnids are arthropods in the Class (biology), class Arachnida () of the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, opiliones, harvestmen, Solifugae, camel spiders, Amblypygi, wh ...

s). Morphology of

Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...

-Devonian arthropd ''

Maldybulakia ''Maldybulakia'' is a genus of freshwater arthropod which lived during Late Silurian to Late Devonian. ''Maldybulakia'' is known from three species, ''M. angusi'' and ''M. malcolmi'' from Australia, ''M. mirabilis'' from Kazakhstan, and ''M. sai ...

'' is sometimes compared to that of ''Willwerathia''. However, in 2020, Lamsdell found that ''Willwerathia'' bears a strong resemblance to the

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

Falcatamacaris ''Falcatamacaris'' is an extinct genus of Cambrian artiopodan arthropod, only known from the type species ''F. bellua'' described in 2014, from the Guzhangian (Cambrian Stage 3) aged Weeks Formation in Utah Utah is a landlocked state in ...

'', while it does not bear resemblance to other chelicerates.

References

{{Taxonbar, from=Q99774735 Xiphosura Synziphosurina Devonian animals of Europe Fossils of Germany Fossil taxa described in 1969 Prehistoric arthropod genera