''Holmipterus'' is a problematic genus of

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

, an extinct group of aquatic

arthropods 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 ...

. The type and only species of ''Holmipterus'', ''H. suecicus'', is known from deposits of Middle

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 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 shortest period of the Paleozo ...

age in the

Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...

. The generic name honours , a renowned Swedish palaeontologist specialising in

and

crustaceans Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

, and the species name ''suecicus'' is

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

for 'Swedish'. Although ''Holmipterus'' was a large eurypterid and is known from multiple, albeit partial and fragmentary, specimens, it has proven difficult to determine where it fits in the eurypterid family tree. This is due to the fossil material referred to ''Holmipterus'' combining traits seen in different eurypterid groups, such as the

Carcinosomatidae Carcinosomatidae (the name deriving from the type genus ''Carcinosoma'', meaning "crab body")Meaning osomaat ''www.dictionary.com''. Retrieved 7 September 2018. is a family of eurypterids, an extinct group of aquatic arthropods. They were member ...

and

Megalograptidae Megalograptidae are a family of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions". The megalograptids were likely the first major successful group of eurypterids, evidenced by a Late Ordovician radiation. ...

, and has some distinctive features, such as a

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

(the posteriormost division of the body) with two articulating 'cercal blades', forming an organ capable of grasping. Though often classified either as a carcinosomatid or megalograptid, ''Holmipterus'' has also been classified as a genus of uncertain affinity within the

Eurypterina Eurypterina is one of two suborders of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions". Eurypterine eurypterids are sometimes informally known as "swimming eurypterids". They are known from fossil deposi ...

suborder, or within the entire

Eurypterida Eurypterids, often informally called sea scorpions, are a group of extinct arthropods that form the order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period 467.3 million years ago. The group is ...

order. It is possible that the original 1979 description of ''Holmipterus suecicus'' reconstructed the telson inaccurately, and/or mistakenly combined fossil material actually belonging to two different genera.

Description

Although the precise size of ''Holmipterus'' is uncertain, the size of its fossils means that it must have been a relatively large eurypterid. Estimates based on the specimen indicates a length of around one metre. The most distinctive feature of ''Holmipterus'' was its

(the posteriormost division of its body), which was unique among the eurypterids. Per the description, the pretelson (the segment immediately preceding telson) not only supports a spike-shaped and thin, yet robust, telson, but also two articulating 'cercal blades', meaning that the pretelson-telson assemblage could function as a 'formidable grasping weapon'. As (other) Carcinosomatoid eurypterids could, it is possible that ''Holmipterus'' could push its tail up "overhead", similar to a scorpion. The telson itself was curved downwards and had a serrated and flat platform near the base. The most complete telson found measured 8.65 centimetres (3.4 in) in length and was 1.46 centimetres (0.57 in) wide at the widest part of the serrated platform. Larger, less complete specimens are known, including a telson which was 1.82 centimetres (0.72 in) wide at the same point. The telson of ''Holmipterus'' was similar to that of the eurypterid ''

Megalograptus ''Megalograptus'' is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of ''Megalograptus'' have been recovered in deposits of Katian (Late Ordovician) age in North America. The genus contains five species: ''M. alveolatu ...

''. Although the description was based on multiple specimens, given that no other eurypterid preserves articulating cercal blades, other than ''Megalograptus'', and the fragmentary or partial nature of most of the fossil material, the accuracy of the description in regards to the reconstruction of the telson, in particular the cercal blades, has been questioned. The

chelicerae The chelicerae () are the mouthparts of the subphylum Chelicerata, an arthropod group that includes arachnids, horseshoe crabs, and sea spiders. Commonly referred to as "jaws", chelicerae may be shaped as either articulated fangs, or similarly ...

(frontal appendages) had four joints, with a long, narrow and falcate (with a curvature similar to that of the sickle) chelae (claws) 12.4 mm (0.49 in) long. The hand was about as broad as long, with a socket for the articulation of the

condyle A condyle (;Entry "condyle"
in
spines, one on each side. These walking legs are characteristic of the group

in which the legs were flattened and with the venter (abdomen) turned

anteriorly Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

. They were different from the highly differentiated legs of ''Megalograptus''. The spines of the walking legs were striated with narrow and longitudinal ridges along the back of the curved part. The swimming legs are known for a paddle retaining the sixth and seventh segments. The triangular lobe of the sixth joint was very long with linear

scales Scale or scales may refer to: Mathematics * Scale (descriptive set theory), an object defined on a set of points * Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original * Scale factor, a number w ...

along most of the posterior border which grade into serrated scales at the

distal Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

end. The seventh joint was large and finely serrated along the anterior edge and increasingly thick along the distal end. The eighth joint was a small triangular spine. An epimera (the part of a segment next to an articulation of an appendage) of the first

tergite A ''tergum'' (Latin for "the back"; plural ''terga'', associated adjective tergal) is the dorsal ('upper') portion of an arthropod segment other than the head. The anterior edge is called the 'base' and posterior edge is called the 'apex' or 'mar ...

whose edge slopes back proves that the entire

mesosoma The mesosoma is the middle part of the body, or tagma, of arthropods whose body is composed of three parts, the other two being the prosoma and the metasoma. It bears the legs, and, in the case of winged insects, the wings. In hymenopterans of t ...

was very tumid, as in the carcinosomatids. It is possible that the original description of ''Holmipterus'' is in error and that the fossil material actually belongs to two different genera.

History of research

Fossils of ''Holmipterus'' have been found at the 'Vattenfallet' site in the southern outskirts of

Visby Visby () is an urban area in Sweden and the seat of Gotland Municipality in Gotland County on the island of Gotland with 24,330 inhabitants . Visby is also the episcopal see for the Diocese of Visby. The Hanseatic city of Visby is arguably th ...

on the island of

Gotland Gotland (, ; ''Gutland'' in Gutnish), also historically spelled Gottland or Gothland (), is Sweden's largest island. It is also a province, county, municipality, and diocese. The province includes the islands of Fårö and Gotska Sandön to the ...

in Sweden, in deposits of Early Wenlock (Middle Silurian) age. Though they were first figured by , a renowned Swedish palaeontologist specialising in

and

, in the early 20th century, Holm never released or published these figures. ''Holmipterus suecicus'' was described in 1979 by Erik N. Kjellesvig-Waering, with the generic name honouring Holm and the species name ''suecicus'' being

for 'Swedish'. Erik N. Kjellesvig-Waering based the creation of the new genus mainly on the highly distinct telson, but also included some partial and fragmentary specimens consisting of other body parts, such as the appendages and the main body, without comment as to why. Whether all specimens should be accommodated within one genus has been questioned by some later researchers.

Classification

The pretelson of ''Holmipterus'' was rounded in its cross-section, which suggests that the genus belonged to one of the three families in the superfamily

Carcinosomatoidea Carcinosomatoidea is an extinct superfamily of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions". It is one of the superfamilies classified as part of the suborder Eurypterina. Some carcinosomatoid genera ...

Mixopteridae The Mixopteridae are a family of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions". The family is one of two families contained in the superfamily Carcinosomatoidea (along with Carcinosomatidae), which in ...

. In the original 1979 description, Kjellesvig-Waering assigned ''Holmipterus'' to the family Megalograptidae, but noted that "There is little doubt in my mind that ''Holmipterus'' is so different from ''Megalograptus'' that when more specimens of the former are known, it will be best to separate them into different families." In 1989, Victor P. Tollerton referred the genus, though noted that this was uncertain, to the Carcinosomatidae based on the fragmentary fossils of the leg and the incomplete swimming paddle. Tollerton noted that he believed Kjellesvig-Waering's original description to be in error, especially in regards to the reconstruction of the telson (particularly the cercal blades) and that it was likely that the original fossil material actually belonged to two different genera. In a 2007 study, O. Erik Tetlie noted that ''Holmipterus'' as a megalograptid was a "very questionable" classification and listed it as a genus with uncertain affinity within the

suborder. In 2009, James C. Lamsdell and Simon J. Braddy classified ''Holmipterus'' as a megalograptid, but in 2015, Lamsdell and colleagues recovered ''Holmipterus'' as a basal carcinosomatid in a phylogenetic analysis. The cladogram below follows the analysis by Lamsdell ''et al''. (2015). The ''Summary List of Fossil Spiders and Their Relatives'', a document compiled by Jason A. Dunlop, David Penney and Denise Jekel, classified ''Holmipterus'' as Eurypterida ''

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...

'' in its 2015Dunlop, J. A., Penney, D. & Jekel, D. 2015
A summary list of fossil spiders and their relatives
In World Spider Catalog. Natural History Museum Bern and 2018 editions, indicating an uncertain taxonomic position within the Eurypterida as a whole.Dunlop, J. A., Penney, D. & Jekel, D. 2018
A summary list of fossil spiders and their relatives
In World Spider Catalog. Natural History Museum Bern

Palaeoecology

The deposits in which ''Holmipterus'' was discovered was once a

reef A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic processes— deposition of sand, wave erosion planing down rock out ...

environment that supported a diverse fauna and flora. The presence of fossilised algae in the deposits indicate that the environment was within the photic zone, and the presence of dasycladaceaean algae indicate that the depth of the sea never reached more than 100 metres (330 ft). The fossils referred to ''Holmipterus suecicus'' were recovered alongside fossils of four other eurypterid species: ''

Eurypterus ''Eurypterus'' ( ) is an extinct genus of eurypterid, a group of organisms commonly called "sea scorpions". The genus lived during the Silurian period, from around 432 to 418 million years ago. ''Eurypterus'' is by far the most well-studied and ...

serratus'', '' Dolichopterus gotlandicus'', ''

Erettopterus ''Erettopterus'' is a genus of large predatory eurypterid, an extinct group of aquatic arthropods. Fossils of ''Erettopterus'' have been discovered in deposits ranging from Early Silurian (the Rhuddanian age) to the Early Devonian (the Lochkov ...

serricaudatus'' and ''Erettopterus carinatus''. Alongside the other eurypterids, a large number of other organisms have been recovered, including the aforementioned algae,

sponges 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 ...

foraminiferans Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly an ...

, chitinozoans, melanosclerites,

corals Corals are marine invertebrates within the class (biology), class Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important C ...

polychaetes Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are mad ...

, monoplacophorans,

chitons Chitons () are marine molluscs of varying size in the class Polyplacophora (), formerly known as Amphineura. About 940 extant and 430 fossil species are recognized. They are also sometimes known as gumboots or sea cradles or coat-of-mail shel ...

gastropods The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. Ther ...

bivalves Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

, rostroconchs,

cephalopods A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, an ...

trilobites Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the At ...

, phyllocarids, ostracodes,

bryozoans Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called a l ...

brachiopods Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, whi ...

, tentaculitans, machaeridians,

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 ...

echinoderms An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea li ...

and

agnathans Agnatha (, Ancient Greek 'without jaws') is an infraphylum of jawless fish in the phylum Chordata, subphylum Vertebrata, consisting of both present (cyclostomes) and extinct (conodonts and ostracoderms) species. Among recent animals, cyclostomes ...

. In total, almost five hundred different fossil species are known from the site.

References

{{Taxonbar, from=Q5883762 Carcinosomatoidea Silurian eurypterids Fossils of Sweden Eurypterids of Europe

Description

History of research

Classification

Palaeoecology

See also

References