page_title: Adelophthalmidae
section_title: History of research
hierarchical_section_title: Adelophthalmidae / History of research
caption_attribution_description: Palaeontographica. Beiträge zur Naturgeschichte der Vorwelt. Herausgegeben von Wilh. Dunker und Herm. von Meyer. Vierter Band. Cassel, Druck und Verlag von Theodor Fischer. 1851.
context_page_description: Adelophthalmidae is a family of eurypterids, an extinct group of aquatic arthropods. Adelophthalmidae is the only family classified as part of the superfamily Adelophthalmoidea, which in turn is classified within the infraorder Diploperculata in the suborder Eurypterina.
  Adelophthalmid eurypterids were small and swimming eurypterids that appeared in the Silurian period. With the earliest known members of the group, Nanahughmilleria prominens and Parahughmilleria maria, being known from deposits of Early Silurian age and the very last members, belonging to the long-lasting and widespread genus Adelophthalmus, going extinct in the Early Permian, the Adelophthalmidae is the longest lasting single family of eurypterids. The survival of the group, and of swimming eurypterids beyond the Late Devonian is entirely due to the survival, and subsequent success, of Adelophthalmus throughout the Devonian and Carboniferous. Adelophthalmus represents the only known genus of swimming eurypterids beyond the extinction of the rest of the group in the Late Devonian, extending the temporal range of the group by over a hundred million years.
context_section_description: The first adelophthalmid fossils to be uncovered were those of the type genus, Adelophthalmus. The German paleontologist Hermann Jordan collected the first specimen of the species A. granosus at Jägersfreude in Saarland, Germany. The specimen would be described three years later by Jordan and Hermann von Meyer, who immediately recognized the eurypterid nature of the fossils by the great resemblance of the overall shape and form of the carapace and appendages with that of Eurypterus. One of the main differences that Jordan and von Meyer noticed was the apparent lack of eyes, which gives name to Adelophthalmus (meaning "no obvious eyes") and the entire superfamily. This feature is now assumed to be due to a preservational artifact and that was not present in Adelophtalmus, nor in any other adelophthalmid. Since then, a total of 32 species have been described, some of which have been historically classified within other genera (Anthraconectes, Glyptoscorpius, Lepidoderma and Polyzosternites, all now synonymous with Adelophthalmus), making Adelophthalmus the most diverse eurypterid genus to date. However, many of these species are fragmentary and could represent synonyms of other species within Adelophthalmus or even species of other genera. It is possible that the large amount of species in Adelophthalmus will eventually provoke its separation into two or three separate genera.
  In 1948, the Ukrainian paleontologist and geologist Boris Isidorovich Chernyshev described a new genus known by one single specimen from Kazakhstan (at that time part of the Soviet Union) and tentatively classified it as part of the Pterygotidae family. It was named Unionopterus, and its classification is controversial due to the poor illustrations given by Chernyshev and the fact that the only known fossil is presumed to be lost. The genus has been treated as an indeterminate eurypterid, an adelophthalmid or a member of the genus Adelophthalmus, as well as completely ignored. The spinosity of its appendages may suggest the second option, but this is not entirely certain and the phylogenetic classification of Unionopterus may never be resolved.
  In 1961, the American paleontologist Erik Norman Kjellesvig-Waering considered several species of the genus Hughmilleria sufficiently different from the type species to be separated into a new subgenus, which he named Nanahughmilleria. These species shared a key characteristic, small intramarginal eyes of reniform form (bean-shaped), in contrast to the large ovoid eyes placed in the margin of the carapace present in the genotype and its allied forms. Kjellesvig-Waering designated H. (Nanahughmilleria) norvegica as the type species of the new subgenus. At the same time, he erected a new genus, Parahughmilleria, with P. salteri as the type species. Kjellesvig-Waering based its new clade mainly on the presence of supplementary lobes (distal lobes in a plate-like segment which contains the genital aperture called genital operculum), as well as in the intramarginal eyes.
  In 1964, Kjellesvig-Waering described the genital operculum of the species H. (N.) phelpsae and suggested that this part of the body could have great phylogenetic importance in the future. Two years later, together with the American paleontologist Kenneth Edward Caster, he raised H. (N.) phelpsae to the generic level under the name Pittsfordipterus. They also described a new genus and species, Bassipterus virginicus. It differs essentially from other adelophthalmids by the specialization of its genital appendage, with characteristics reminiscent of Eurypterus.
  In 1989, Victor P. Tollerton Jr. described the family Adelophthalmidae along with many others, including Adelophthalmus, Parahughmilleria, Bassipterus and Unionopterus. This clade was based on the presence of spines in the second to fifth pair of appendages, a swimming leg of Adelophthalmus-type and the presence of epimera (lateral "extensions" of the segment) in the seventh segment. Tollerton commented that some species of Adelophthalmus that did not have spines in the appendages may be bett
caption: The type specimen of Adelophthalmus granosus, the first adelophthalmid ever described.
exif: {}