species. Over 100 fossil species of scorpion have been described. The oldest found as of 2021 is Dolichophonus loudonensis, which lived during the Silurian, in present-day Scotland. Gondwanascorpio from the Devonian is among the earliest-known terrestrial animals on the Gondwana supercontinent. Some Palaeozoic scorpions possessed compound eyes similar to those of eurypterids. The Triassic fossils Protochactas and Protobuthus belong to the modern clades Chactoidea and Buthoidea respectively, indicating that the crown group of modern scorpions had emerged by this time. Phylogeny The Scorpiones are a clade within the pulmonate Arachnida (those with book lungs). Arachnida is placed within the Chelicerata, a subphylum of Arthropoda that contains sea spiders and horseshoe crabs, alongside terrestrial animals without book lungs such as ticks and harvestmen. The extinct Eurypterida, sometimes called sea scorpions, though they were not all marine, are not scorpions; their grasping pincers were chelicerae, not homologous with the pincers (second appendages) of scorpions. Scorpiones is sister to the Tetrapulmonata, a terrestrial group of pulmonates containing the spiders and whip scorpions. This 2019 cladogram summarizes: Recent studies place pseudoscorpions as the sister group of scorpions in the clade Panscorpiones, which together with Tetrapulmonata makes up the clade Arachnopulmonata. The internal phylogeny of the scorpions has been debated, but genomic analysis consistently places the Bothriuridae as sister to a clade consisting of Scorpionoidea and Chactoidea. The scorpions diversified between the Devonian and the early Carboniferous. The main division is into the clades Buthida and Iurida. The Bothriuridae diverged starting before temperate Gondwana broke up into separate land masses, completed by the Jurassic. The Iuroidea and Chactoidea are both seen not to be single clades, and are shown as "paraphyletic" (with quotation marks) in this 2018 cladogram. Taxonomy Carl Linnaeus described six species of scorpion in his genus Scorpio in 1758 and 1767; three of these are now considered valid and are called Scorpio maurus, Androctonus australis, and Euscorpius carpathicus; the other three are dubious names. He placed the scorpions among his "Insecta aptera" (wingless insects), a group that included Crustacea, Arachnida and Myriapoda. In 1801, Jean-Baptiste Lamarck divided up the "Insecta aptera", creating the taxon Arachnides for spiders, scorpions, and acari (mites and ticks), though it also contained the Thysanura (thrips), Myriapoda and parasites such as lice. German arachnologist Carl Ludwig Koch created the order Scorpiones in 1837. He divided it into four families, the six-eyed scorpions "Scorpionides", the eight-eyed scorpions "Buthides", the