Tanystropheus

Tanystropheus (~ 'long' + 'hinged') is an extinct genus of archosauromorph reptile which lived during the Triassic Period in Europe, Asia, and North America. It is recognisable by its extremely elongated neck, longer than the torso and tail combined. The neck was composed of 13 vertebrae strengthened by extensive cervical ribs. Tanystropheus is one of the most well-described non-archosauriform archosauromorphs, known from numerous fossils, including nearly complete skeletons. Some species within the genus may have reached a total length of , making Tanystropheus the longest non-archosauriform archosauromorph as well. Tanystropheus is the namesake of the family Tanystropheidae, a clade collecting many long-necked Triassic archosauromorphs previously described as "protorosaurs" or "prolacertiforms".

Tanystropheus contains at least two valid species as well as fossils which cannot be referred to a specific species. The type species of Tanystropheus is T. conspicuus, a dubious name applied to particularly large fossils from Germany and Poland. Complete skeletons are common in the Besano Formation at Monte San Giorgio, on the border of Italy and Switzerland. Monte San Giorgio fossils belong to two species: the smaller T. longobardicus and the larger T. hydroides. These two species were formally differentiated in 2020 primarily on the basis of their strongly divergent skull anatomy. When T. longobardicus was first described in 1886, it was initially mistaken for a pterosaur and given the name "Tribelesodon". Starting in the 1920s, systematic excavations at Monte San Giorgio unearthed many more Tanystropheus fossils, revealing that the putative wing bones of "Tribelesodon" were actually neck vertebrae.