page_title: Adelophthalmus
section_title: Earliest discoveries
hierarchical_section_title: Adelophthalmus / History of research / Earliest discoveries
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: 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. Adelopthtalmus 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, Australia, which indicates that Adelophthalmus might have had a nearly cosmopolitan 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.
context_section_description: 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.
  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 erronously be considered to represent the fossil remains of a scorpion and not an 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, Ameri
caption: The type specimen of A. granosus, MB.A. 890, as illustrated in its original description by Hermann Jordan and Hermann von Meyer in 1854. The apparently eyeless carapace can be seen in the bottom-left illustration.
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