Earliest discoveries in 1854. The apparently eyeless carapace can be seen in the bottom-left illustration. The first specimen of
Adelophthalmus to be discovered was excavated in 1851 by German paleontologist Hermann Jordan in a railway shaft at Jägersfreude, near
Saarbrücken in Germany. This specimen was described three years later in 1854 in the work
Ueber die Crustaceen der Steinkohlenformation von Saarbrücken ("Of the crustaceans of the coal formation of Saarbrücken"), written by Jordan and
Hermann von Meyer and featuring descriptions of several other arthropod taxa. The fossil was immediately recognized by Jordan as that of a eurypterid, with both the overall shape and form and the individual parts (particularly the head and the appendages) being very similar to those of
Eurypterus which had been described in the United States in 1825, 29 years earlier. Among the differences noted between the specimens were the smaller size and later age of the Saarbrücken fossil and what Jordan and von Meyer perceived to be a complete lack of eyes. Since the preserved carapace had no indication of there ever having been any eyes present, Jordan and von Meyer assumed that the animal would have been completely eyeless in life, with the original description of the fossil citing several cases in which eyeless forms occur in arthropod groups otherwise possessing eyes (such as in crustaceans and trilobites). This apparent eyelessness prompted the choice of name
, Adelophthalmus, meaning "no obvious eye". The species name,
granosus, is derived from the Latin
grānōsus ("grainy" or "full of grains"), referring to the state of the fossil preservation having given some of the fossils a grainy texture. The type specimen, to this day the only specimen referred to
A. granosus, is today held in the arthropod paleontology collections of the
Natural History Museum of Berlin under the specimen number MB.A. 890. of
Frankfurt. Though modern researchers tend to treat the assumed eyelessness as a preservational artifact and not a feature that
A. granosus would have had in life, this issue was not resolved immediately which made the naming of subsequently discovered species confusing and problematic.
Lepidoderma imhofi, named in 1855 from Carboniferous-age deposits in Germany, shows definite eyes. The descriptor, Austrian paleontologist
August Emanuel von Reuss, noted that
Lepidoderma likely was synonymous with
Adelophthalmus, but ignored the rules of taxonomical priority and used his younger name due to it being based on material that he considered to be better preserved.''
The name Lepidoderma
derives from the Latin lepidus'' ("elegant" or "fine") and Ancient Greek δέρμα (ðerma, "skin"). In 1868, American paleontologists
Fielding Bradford Meek and
Amos Henry Worthen described
Anthraconectes mazonensis,
Anthraconectes being designated a
subgenus of
Eurypterus, based on fossils recovered in Carboniferous-age deposits at
Mazon Creek in Illinois (the first species to be described from North America).''
After examining the Adelophthalmus
type specimen in 1934, German paleontologist Paul Guthörl remarked that Anthraconectes
and Adelophthalmus
were so similar that they would have been synonyms had Adelophthalmus
possessed eyes. The name Polyzosternites
was coined by German paleontologist Friedrich Goldenberg (who also named the species Polyzosternites raniceps
, today recognized as A. raniceps
) in 1873 to replace the name Adelophthalmus
in regards to specimens described after the type specimen in the belief that the type of Adelophthalmus
represented the fossil remains of a cockroach. Glyptoscorpius
was erected to include some fossils from the Carboniferous of Scotland, including the species G. perornatus
(designated as type, the type specimen consisting of only five tergites), G. caledonicus
and G. kidstoni
, by British geologist Ben Peach in 1882. Glyptoscorpius
would for a long time erroneously be considered to represent the fossil remains of a scorpion and not a eurypterid.'' The second species to be described from North America was
A. pennsylvanicus (as
Eurypterus pennsylvanicus), by Meek and Worthen from the coal-measures of
Venango County, Pennsylvania in 1877. That same year, American paleontologist
James Hall described the species
A. mansfieldi (under the name
Eurypterus (
Dolichopterus)
mansfieldi) based on fossils recovered in
Cannelton, Pennsylvania.''
In 1888, Hall described the species A. approximatus
(as Eurypterus approximatus
) together with American paleontologist John Mason Clarke based on fossils also recovered from Pennsylvania.'' The English geologist
Henry Woodward described the species
Eurypterus wilsoni (=
Adelophthalmus wilsoni) in 1888 based on a fossil recovered by an Edward Wilson of the
Bristol Museum, naming the species in his honor. The only known specimen is composed of six body segments and Woodward noted that naming the species may have been slightly premature. He noted that the specimen possessed markings and spikes running alongside the abdomen in a similar way to
A. mansfieldi (then classified as
Eurypterus mansfieldi).'''' Portuguese paleontologist Pereira de Lima described the species
Eurypterus douvillei (today seen as
Adelophthalmus douvillei) in 1890 based on fossils from
Bussaco in Portugal.''''
Twentieth century dumonti
).In 1907, Henry Woodward described Eurypterus moyseyi
(today recognized as Adelophthalmus moyseyi
) based on fossils recovered from Radstock, Somerset in England. Woodward compared the singular specimen of E. moyseyi
to fossil specimens of A. mansfieldi
from America, finding the spikes along the abdomen very similar, though noted that they were less prominent in E. moyseyi
. Woodward described very large fossil specimens, the carapace alone measuring 21 cm (8.3 in) and the seven associated body segments measuring an additional 25 cm (9.8) together. Despite this, the latest available size estimates for A. moyseyi'' put the species at 12 cm (4.7 in) in length.
A. nebraskensis was described as
Eurypterus (
Anthraconectes)
nebraskensis in 1914 by American geologist
Erwin H. Barbour based on fossils recovered in Nebraska, USA. The species was described alongside other fossils from the associated sediments, which helped reinforce the idea as
Adelophthalmus (or
Anthraconectes) as a freshwater animal. The species
A. dumonti, Carboniferous in age, was described by Belgian paleontologist Xavier Stainier in 1915 as
Eurypterus dumonti. The type specimen, a relatively complete fossil measuring just 3.3 centimetres (1.3 in) in length, was discovered through
boring at a new coalfield in
Campine, northern Belgium. Though the fossil had been slightly damaged, including the entire
counterpart being fragmented, owing to careless usage of hammers and diamond bores during excavation, the fossil could nevertheless be studied in detail and compared to known eurypterid species. As Stainier
considered every known Carboniferous eurypterid to be part of the genus
Eurypterus (among them several species today recognized as
Adelophthalmus, such as the type species
A. granosus,
A. imhofi and
A. pennsylvanicus), he classified the new Belgian eurypterid in that genus as well. He did note that the new species was very similar to species such as
E. pennsylvanicus and especially
E. mansfieldi (both seen as species of
Adelophthalmus today). The species name
dumonti honors the prominent Belgian geologist
André Dumont. The American geologist
Amadeus William Grabau described the species
Anthraconectes chinensis in 1920, based on fossils discovered in Zhaozezhuang, China.'''' Canadian geologist
Walter A. Bell described the species
A. bradorensis in 1922 (as a species of
Anthraconectes) based on a single fossil recovered in New Campbelton in the
Municipality of the County of Victoria,
Canada, referring it to the genus due to similarities with the Scottish
A. kidstoni and the American
A. mansfieldi. 1924 saw the description of the species
Anthraconectes sellardsi by American paleontologist
Carl Owen Dunbar based on two incomplete fossils and few other small fragments from Elmo in Kansas. The first specimen preserves the carapace and the first four tergites of the preabdomen, while the second preserves five preabdominal and three postabdominal tergites; this specimen represents twice the size of the first one. The species
A. oklahomensis was described by American paleontologist Carl E. Decker in 1938 based on Permian-age fossils in Oklahoma. Since the
A. oklahomensis specimen was virtually identical to specimens of
A. sellardsi of similar age and a similar stratigraphical horizon in Kansas,
A. oklahomensis was designated a junior synonym of
A. sellardsi by American geologist Carl Colton Branson, with the support of Decker, in 1959. The type specimen of
A. zadrai, MB.A. 889, was collected in the Czech Republic in 1930 or 1931 and first mentioned in a manuscript by French Carboniferous worker Pierre Pruvost, who dubbed it "
Eurypterus (Anthraconectes) Zadrai", but he did not formally describe the specimen or taxon. Pruvost had previous experience with the genus, having described the species
Anthraconectes cambieri in 1930 based on fossils from
Charleroi, Belgium.
A. zadrai was first described formally in 1952 as
Adelophthalmus zadrai, at a point in time when the type specimen was seemingly lost. The specimen was rediscovered in
Berlin under a different species name based on the original collector of the fossil (Dr. Palisa) and without any designation of it representing a type specimen. Pruvost was also honored through the naming of
A. pruvosti (described as
Lepidoderma pruvosti by Norwegian paleontologist Erik N. Kjellesvig-Waering in 1948 based on fossils discovered in
Lens, France).'''' 1933 saw Ukrainian paleontologist Boris Isidorovich Chernyshev describe the species
A. carbonarius based in one single specimen from the
Donets in Ukraine. A new expedition in 2012 carried out by Russian paleontologist Evgeniy S. Shpinev and others in the respectively Russian and Ukrainian localities of Kakichev and Lomuvatka brought a number of well-preserved, presumably juvenile, fossils of
A. carbonarius. The exact identification of these fossils is not possible, but they are identified as
A. carbonarius since there are no features showing the opposite. Another Belgian species,
A. corneti, was described by Pruvost in 1939 based on fossils from
Quaregnon.'''' All synonymous genera;
Anthraconectes,
Glyptoscorpius,
Lepidoderma and
Polyzosternites, were subsumed into
Adelophthalmus in studies during the middle twentieth century, notably that of Belgian paleontologist Fredrik Herman van Oyen (1956). Though most authors assign all described species to
Adelophthalmus, some, such as van Oyen in 1956, have considered
Anthraconectes to potentially represent a distinct genus, citing that scorpions with similar dorsal anatomies can be quite different ventrally and that the same could be true for the Carboniferous
Adelophthalmus where the ventral morphology is not yet known. A genus
Anthraconectes of this nature would be problematic due to its classification depending on the preservational state of any given specimen.
A. asturica was described as
Lepidoderma asturica by Spanish paleontologist Bermudo Meléndez in 1971 based on fossils from d'Ablana in Spain.'''' The species
A. luceroensis was described by American paleontologists Barry S. Kues and Kenneth K. Kietzke in 1981 based on 150 fossil specimens recovered from the
Madera Formation of New Mexico. The large amount of specimens recovered, representing individuals at various stages of development and ontogeny, allowed detailed studies to be performed on the ontogeny and intraspecific variation within
Adelophthalmus. American paleontologist Roy E. Plotnick referred a species of
Eurypterus,
E. lohesti (first described in 1889) to
Adelophthalmus in 1983 (as
A. lohesti), but this classification is questionable as the morphology of the
A. lohesti specimen is not consistent with that otherwise known of
Adelophthalmus. The differences include
A. lohesti having larger eyes, a wider carapace and what could possible by a median ridge on the carapace.
Twenty-first century In 2004, the German paleontologist Markus Poschmann referred the species
A. sievertsi, first described as part of the genus
Rhenopterus by Norwegian paleontologist Leif Størmer in 1969 based on fossil remains from the Devonian
Klerf Formation in Germany, to the genus. Poschmann also referred the species
Rhenopterus waterstoni (described earlier in 2004 based on the singular specimen BMNH In 60174 from the Late Devonian of Australia) to
Adelophthalmus. This species had previously not been assigned to the genus despite clear similarities to other species of
Adelophthalmus partly due to there previously not being any solid evidence for the presence of
Adelophthalmus as early as the Devonian.
A. irinae was described in 2006 based on a fossil specimens (including the holotype, a prosoma, "head", with the specimen number PIN no. 5109/4) collected by the Krasnoyarsk Geological Expedition near Sakhapta, a village in the
Nazarovsky District of the
Krasnoyarsk Region of
Russia. The fossils, from the Tournaisian Solomennyi Stan Formation, could confidently be assigned to
Adelophthalmus based on their scalelike ornamentation, the position of their eyes and the shape of the carapace shortly after their excavation. The species is the first species of
Adelophthalmus to be described from Russia and the first ever Carboniferous eurypterid known from the country. It is also one of few Carboniferous eurypterids found within the territory of the former
Soviet Union, the only others being
A. carbonarius from
Ukraine and
Unionopterus from
Kazakhstan. Shpinev described two new species of
Adelophthalmus in 2012;
A. kamyshtensis and
A. dubius (the name deriving from the Latin
dubius = "doubtful"), both based on fossils originally collected by Russian geologist Yuriy Fedorovich Pogonya-Stefanovich in 1960 in deposits 3 km southeast of the village of Kamyshta (which lent its name to
A. kamyshtensis) of the
Republic of Khakassia, Russia and now housed at the
Borissiak Paleontological Institute. Despite how poorly preserved these fossils are, several features (notably the parabolic carapace and the presence of spikes along the abdomen) place both species within
Adelophthalmus. In 2013,
A. piussii became the first eurypterid to be described from
Italy. The specimen (specimen number MFSNgp 31681, housed at the Museo Friulano di Storia Naturale in
Udine) was collected in the gravel bank of a small creek near the greater Bombaso creek, north of the village of
Pontebba and consists of a
carapace and seven opisthosomal segments on a large block of sandstone. The name of the species,
piussii, honors the collector of the type specimen, Stefano Piussi. In 2018, Shpinev and Russian researcher A. N. Filimonov described a new species named
A. khakassicus based in many well-preserved specimens. Found in the
Ilemorovskaya Formation of Khakassia (hence the name) in 2014 by Filimonov, it represents the biggest species of the genus. The holotype, PM TGU 168/108, is composed of parts of the metasoma and a complete telson, with several other known paratypes. As
A. khakassicus is known from similar stratigraphic levels to those of
A. kamyshtensis and
A. dubius, it has been suggested that these three species could represent synonyms. In 2020, Lamsdell, Victoria E. McCoy, Opal A. Perron-Felle and Melanie J. Hopkins described a new species of
Adelophthalmus from the Tournaisian stage of (most likely) the
Lydiennes Formation, in France. Its only known specimen, GLAHM A23113, is a nearly complete body only lacking the telson and preserved in
phosphatic nodules. For this reason, it was called
Adelophthalmus pyrrhae, named after
Pyrrha of Thessaly, a figure from
Greek mythology who, together with her husband
Deucalion, threw stones that transformed into babies to repopulate the world. The good preservation of
A. pyrrhae allowed researchers to examine parts of its
respiratory system, and after their study it was confirmed that even if they had a mostly aquatic lifestyle, the eurypterids could venture on to land for long periods. == Evolutionary history ==