Adelophthalmus

Adelophthalmus Temporal range: Early Devonian–Early Permian, 407.6–283.5 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Fossil specimen of A. mansfieldi illustrated by James Hall
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Chelicerata
Order:	†Eurypterida
Superfamily:	†Adelophthalmoidea
Family:	†Adelophthalmidae
Genus:	†Adelophthalmus Jordan in Jordan & von Mayer, 1854[1]
Type species
†Adelophthalmus granosus Jordan in Jordan & von Meyer, 1854[1]
Species
33 species †A. approximatus (Hall & Clarke, 1888) †A. asturica (Melendez, 1971) †A. bradorensis (Bell, 1922) †A. cambieri (Pruvost, 1930) †?A. carbonarius Chernyshev, 1933 †A. chinensis (Grabau, 1920) †A. corneti (Pruvost, 1939) †A. douvillei (de Lima, 1890) †A. dubius Shpinev, 2012 †A. dumonti (Stainier, 1915) †A. granosus Jordan, 1854 †A. imhofi (Reuss, 1855) †A. irinae Shpinev, 2006 †A. khakassicus Shpinev & Filimonov, 2018 †A. kamyshtensis Shpinev, 2012 †A. kidstoni (Peach, 1888) †?A. lohesti (Dewalque, 1889) †A. luceroensis Kues & Kietzke, 1981 †A. mansfieldi (Hall, 1877) †A. mazonensis (Meek & Worthen, 1868) †A. moyseyi (Woodward, 1907) †A. nebraskensis (Barbour, 1914) †A. pennsylvanicus (Hall, 1877) †?A. perornatus (Peach, 1882) †A. piussii Lamsdell, Simonetto & Selden, 2013 †A. pruvosti (Kjellesvig-Waering, 1948) †A. pyrrhae Lamsdell et al., 2020 †?A. raniceps (Goldenberg, 1873) †A. sellardsi (Dunbar, 1924) †A. sievertsi (Størmer, 1969) †A. waterstoni (Tetlie et al., 2004) †A. wilsoni (Woodward, 1888) †A. zadrai Přibyl, 1952
Synonyms
Genus synonymy Lepidoderma Reuss, 1855 Anthraconectes Meek & Worthen, 1868 Polyzosternites Goldenberg, 1873 Glyptoscorpius Peach, 1882 Synonyms of A. mansfieldi Eurypterus stylus Hall, 1884 Synonyms of A. moyseyi Eurypterus derbiensis Woodward, 1907 Synonyms of A. perornatus A. caledonicus Peach, 1882 Synonyms of A. sievertsi Eurypterus trapezoides Størmer, 1974 Synonyms of A. sellardsi A. oklahomensis Decker, 1938

Adelophthalmus is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Adelophthalmus have been discovered in deposits ranging in age from the Early Devonian to the Early Permian, which makes it the longest lived of all known eurypterid genera, with a total temporal range of over 120 million years. Adelopththalmus was the final genus of the Eurypterina suborder of eurypterids and consisted the only known genus of swimming eurypterids from the Middle Devonian until its extinction during the Permian, after which the few surviving eurypterids were all walking forms of the suborder Stylonurina.

Fossils of Adelophthalmus have been described from four continents; North America, Europe, Asia and Australia, which indicates that Adelophthalmus might have had a nearly cosmopolitan (worldwide) distribution, one of few eurypterid genera to achieve one besides potentially Pterygotus. The territorial expansion of Adelophthalmus had begun early, with representatives found in both Siberia and Australia during the Devonian, but it first gained its almost cosmopolitan distribution following the amalgamation of the supercontinent Pangaea during the Carboniferous and Permian.

The generic name Adelophthalmus means "no obvious eye", referencing that the holotype fossil seemingly represented an eyeless eurypterid, with a carapace (head plate) completely lacking any indication of eyes. Though this has caused much subsequent confusion, including the naming of several junior synonyms, the apparent eyelessness of the type specimen is treated by modern researchers as a preservational artifact, and not a feature that any species of Adelophthalmus would have possessed in life.

Adelophthalmus was a genus of comparatively small eurypterids, with species ranging in size from 4 cm (1.6 in, A. douvillei) to 32 cm (12.6 in, A. khakassicus). As of 2020, Adelophthalmus is the most taxonomically diverse of all eurypterid genera, containing 33 species considered valid. This large amount of species, many named long ago, have prompted some researchers to designate Adelophthalmus as a "wastebasket taxon" with poorly known internal relationships and phylogeny. The genus as it is currently seen may form a monophyletic group (a group sharing a common ancestor) but might most appropriately be split into different genera along distinct clades formed within the current confines of the genus.