Tanystropheus (~ 'long' + 'hinged') is an extinct genus of archosauromorph reptile which lived during the Triassic Period in Europe, Asia, and North America. It is recognizable by its extremely elongated neck, longer than the torso and tail combined. The neck is composed of 13 vertebrae, strengthened by long cervical ribs. Tanystropheus is one of the most well-described non-archosauriform archosauromorphs (reptiles closer to dinosaurs and crocodilians than to lizards). It is 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. 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 supposed wing bones of "Tribelesodon" were actually neck vertebrae. T. hydroides was formally distinguished in 2020, mostly on the basis of its distinctive skull and the confirmation that the two different size forms are adults of different species.
Most Tanystropheus fossils hail from marine or coastal deposits of the Middle Triassic epoch (Anisian and Ladinian stages), with some exceptions. For example, a vertebra from Nova Scotia was recovered from primarily freshwater sediments. The youngest unambiguous fossils in the genus are a pair of well-preserved skeletons from the Zhuganpo Formation, a geological unit in China which dates to the earliest part of the Late Triassic (early Carnian stage). The oldest claims of Tanystropheus fossils belong to "T. antiquus", a European species from the latest part of the Early Triassic (late Olenekian stage). T. antiquus has a proportionally shorter neck than other Tanystropheus species, so some paleontologists consider that T. antiquus deserves a separate genus, Protanystropheus. Some studies suggest that T. antiquus is not even part of the family Tanystropheidae, instead being closer to another long-necked early archosauromorph, Dinocephalosaurus. Tanystropheus is unknown from drier environments and its neck is rather stiff and ungainly, suggesting a reliance on water. On the other hand, the limbs and tail lack most adaptations for swimming and are similar to those of land-based reptiles. Recent studies have supported an intermediate position, reconstructing Tanystropheus as an animal equally capable on land and in the water. Despite its length, the neck was lightweight and stabilized by tendons, so it would not have been a fatal hindrance to moving on land. The hindlimbs and the base of the tail were large and muscular, capable of short bursts of active swimming in shallow water. Tanystropheus was most likely a piscivorous (fish-eating) ambush predator. The narrow and tapering skull of T. longobardicus has three-cusped teeth at the back, suited for holding onto slippery prey, while the broader skull of T. hydroides has an interlocking set of large curved fangs at the front, similar to the fully aquatic plesiosaurs.
History and species
Monte San Giorgio species
19th century excavations at Monte San Giorgio, a UNESCO world heritage site on the Italy-Switzerland border, revealed a fragmentary fossil of an animal with three-cusped (tricuspid) teeth and elongated bones. Monte San Giorgio preserves the Besano Formation (also known as the Grenzbitumenzone), a late Anisian-early Ladinian lagerstätte recognised for its spectacular fossils. In 1886, Francesco Bassani interpreted the unusual tricuspid fossil as a pterosaur, which he named Tribelesodon longobardicus. Peyer's discoveries allowed Tribelesodon longobardicus to be recognised as a non-flying reptile, more than 40 years after its original description. Its supposed elongated finger bones were recognized as neck vertebrae, which compared favorably with those previously described as Tanystropheus from Germany and Poland. Thus, Tribelesodon longobardicus was renamed to Tanystropheus longobardicus and its anatomy was revised into a long-necked, non-pterosaur reptile. Specimen PIMUZ T 2791, which was discovered in 1929, has been designated as the neotype of the species.
A small but well-preserved skull and neck, specimen PIMUZ T 3901, was found in the slightly younger Meride Limestone at Monte San Giorgio. Wild (1980) gave it a new species, T. meridensis, based on a set of skull and vertebral traits proposed to differ from T. longobardicus. Later reinvestigations failed to confirm the validity of these differences, rendering T. meridensis a junior synonym of T. longobardicus.
Polish and German species
thumb|[[Type (biology)|Type vertebrae of "Tanystropheus conspicuus", described in 1855|left]]
The first Tanystropheus specimens to be described were found in the mid-19th century. They included eight large vertebrae from the Upper Muschelkalk of Germany, and a partial skeleton from the Lower Keuper of Poland. These geological units occupy part of the Middle Triassic, from the latest Anisian to middle Ladinian stages. They were later regarded as Tanystropheus fossils undiagnostic relative to other species, rendering T. conspicuus a nomen dubium possibly synonymous with T. hydroides.
Over 500 "Tanystropheus conspicuus" specimens have been recovered from a Lower Keuper bonebed near the Silesian village of Miedary. This is the largest known concentration of Tanystropheus fossils, more than double the number collected from Monte San Giorgio. Though the Miedary specimens are individually limited to isolated postcranial bones, they are preserved in three dimensions and show great potential for elucidating the morphology of the genus. The Miedary locality represents an isolated brackish body of water close to the coast, and the abundance of Tanystropheus fossils suggests that it was an animal well-suited for this kind of habitat.
In the late 1900s, Friedrich von Huene named several dubious Tanystropheus species from Germany and Poland. T. posthumus, from the Norian of Germany, was later reevaluated as an indeterminate theropod vertebra and a nomen dubium. Several more von Huene species, including "Procerosaurus cruralis", "Thecodontosaurus latespinatus", and "Thecodontosaurus primus", have been reconsidered as indeterminate material of Tanystropheus or other archosauromorphs. The Gogolin Formation ranges from the upper Olenekian (latest part of the Early Triassic) to the lower Anisian in age. Assuming they belong within Tanystropheus, the fossils of T. antiquus may be the oldest in the genus. Specimens likely referable to T. antiquus are also known from throughout Germany and the fossiliferous Winterswijk site in the Netherlands. and Rieppel (2010). Tanystropheus-like tanystropheid fossils are known from another freshwater formation in North America: the Anisian-age Moenkopi Formation of Arizona and New Mexico.
Small freshwater tanystropheids are known from Petrified Forest National Park (PEFO) in Arizona, including thin cervical vertebrae similar to Tanystropheus, though much smaller. The park's largest Tanystropheus-like cervical is a mere long. First reported in 2025, The PEFO remains are from the Upper Blue Mesa Member of the Chinle Formation, which is dated to the Norian stage, between 223 and 218 million years ago. If they legitimately belong to Tanystropheus, they would indicate that the genus survived in an inland environment at least 14 million years beyond its assumed extinction elsewhere.
Other fossils
Authentic Tanystropheus specimens from the Makhtesh Ramon in Israel were described as a new species, T. haasi, in 2001. However, this species may be dubious due to the difficulty of distinguishing its vertebrae from T. conspicuus or T. longobardicus. Another new species, T. biharicus, was described from Romania in 1975. It has also been considered possibly synonymous with T. longobardicus. A Tanystropheus-like vertebra from the middle Ladinian Erfurt Formation (Lettenkeuper) of Germany was described in 1846 as one of several fossils gathered under the name "Zanclodon laevis". Though likely the first Tanystropheus fossil to be discovered, the vertebra is now lost, and surviving jaw fragments and other fossil scraps of "Zanclodon laevis" represent indeterminate archosauriforms with no relation to Tanystropheus. The youngest Tanystropheus fossil in Europe is a vertebra from the lower Carnian Fusea site in Friuli, Italy. In 2011, fossils from the Lipovskaya Formation of Russia were given the new genus and species Augustaburiania vatagini by A.G. Sennikov. He also named the new genus Protanystropheus for T. antiquus, though a few studies continued to retain that species within Tanystropheus.
Skull of Tanystropheus longobardicus
The skull of Tanystropheus longobardicus is roughly triangular when seen from the side and top, narrowing towards the snout. Some individuals of T. longobardicus have tricuspid teeth along their entire maxilla, while in others up to seven maxillary teeth are single-cusped fangs similar to the premaxillary teeth. Tanystropheus has 13 cervical (neck) vertebrae, most of which are massive, though the two closest to the head are smaller and less strongly developed.
Torso and tail
thumb|PIMUZ T 2817, a large morphotype (T. hydroides) specimen missing only the skull and a portion of the neck
There are 12 dorsal (torso) vertebrae. The tail is long, with at least 30 and possible up to 50 caudal vertebrae. The scapula (upper shoulder blade) has the form of a large semicircular plate on a short, broad stalk. It lies above the coracoid (lower shoulder blade), which is a large oval-shaped plate with a broad glenoid facet (shoulder socket). sit behind the hips in about half of known specimens preserving the area. They occupy the base of the tail, a region which lacks chevrons. The Early Triassic reptile Prolacerta, from South Africa, also became involved upon its discovery. Prolacerta was the namesake of yet another term introduced into the convoluted space of reptile taxonomy: "Prolacertiformes".
As the century progressed, two competing hypotheses for the affinities of Tanystropheus developed from the groundwork set by Peyer. Both hypotheses were justified by patterns of skull fenestration (the shape of holes in the skull behind the eye) and cranial kinesis (the flexibility of joints within the skull). One idea was that Tanystropheus and kin (particularly Macrocnemus and Prolacerta) were ancestral to "lacertilians", an antiquated term for lizards. This hypothesis was supported up until the 1980s by German and Swiss paleontologists, including Rupert Wild, Some publications from the mid-20th century argued that "protorosaurs" were "euryapsids" (reptiles with only an upper temporal fenestra) related to sauropterygians,
In 1975, a paper by South African paleontologist C.E. Gow argued that none of these hypotheses were entirely correct. He proposed that Prolacerta, and by extension Macrocnemus and Tanystropheus, occupied an extinct spur on the reptile family tree near the ancestry of archosaurs, a diverse group of reptiles with lightweight skulls and serrated teeth set in deep sockets. Protorosaurus-, and Prolacerta-like species, were described in the 1970s, not long after the field of paleontology was reinvigorated by the "dinosaur renaissance" in the 1960s and beyond.
Cladistics and Archosauromorpha (1980s-1990s)
left|thumb|Cladistic analyses agree that Tanystropheus belongs within a [[clade or grade of basal archosauromorphs. Many studies from the 1970s to 1990s referred to long-necked basal archosauromorphs as "prolacertiforms" (namesake Prolacerta pictured)]]
In the 1980s, the advent of cladistics saw a paradigm shift in the field of taxonomy, emphasizing monophyletic clades (all-encompassing groups defined by shared ancestry) over other categorization styles. Phylogenetic analyses were invented to evaluate reptile evolution in a quantitative manner, by collecting a set of characteristics in sampled species and then using computational models to find the simplest (most parsimonious) path evolution could take to produce that character distribution. Cladistics stabilized and defined a fundamental split in the family tree of reptiles: one side of the family tree, Lepidosauromorpha, leads to lepidosaurs such as squamates (lizards and snakes) and the tuatara. The other side, Archosauromorpha, leads to archosaurs. Cladistics was one of many lines of evidence that helped to demonstrate the dinosaurian origin of birds. This left crocodilians and birds as the two surviving archosaur groups.
A series of phylogenetic analyses in the late 1980s and 1990s strongly supported the proposal of Gow (1975). Tanystropheus, Macrocnemus, Protorosaurus, and Prolacerta were always placed as members of Archosauromorpha, closer to archosaurs than to squamates. "Protorosauria" and "Prolacertiformes" were used interchangeably for the archosauromorph subgroup encompassing these superficially lizard-like reptiles. Some authors preferred "Protorosauria" for its priority. Most others used "Prolacertiformes" arguing that "Protorosauria" was a name that carried too much historical baggage, since it had previously encompassed non-archosauromorph "euryapsids" like Araeoscelis. additionally qualify as archosauromorphs.
The following cladogram is from Dilkes (1998), a study with a small sample of "prolacertiforms" but closer resemblance to most analyses of the 2000s and 2010s: These results have driven paleontologists to the conclusion that "Protorosauria" / "Prolacertiformes" is not a natural monophyletic clade and fails to adequately describe the structure of Archosauromorpha. In the modern cladistic framework, it could be considered a paraphyletic grade or polyphyletic category of archosauromorphs united by "primitive" characteristics (such as a slender neck and lizard-like body) rather than a shared evolutionary history.
The following cladogram is a simplified representation of the most stable analysis preferred by Spiekman et al. (2021), analysis 4. In this particular analysis, ratio (continuous) characters are included, certain characters are ordered, and five wildcard taxa are excluded before running the analysis: Czatkowiella harae, Tanystropheus "conspicuus", "Tanystropheus antiquus", Orovenator mayorum and Elessaurus gondwanoccidens.|left]]The diet of Tanystropheus has been strongly debated in the past, though most recent studies consider it a piscivorous (fish-eating) reptile.
Paleobiology
Skull biomechanics
In T. hydroides, the connection between the quadrate and squamosal is loose, with the upper extremity of the quadrate hooking into a deep concavity on the squamosal. This would have enabled a degree of flexibility along the quadrate-squamosal contact, allowing the quadrate to swivel around an otic joint. This a condition is a form of cranial kinesis (movement among bones in the cranium) known as streptostyly, which is found in some living lizards. The quadrate is also loosely connected to the pterygoid, and the quadratojugal fails to contact the jugal, two qualities which allow movement of the quadrate without hindrance. While streptostyly is possible in the reconstructed skull, it cannot be demonstrated whether it was actively used by the living animal. The portion of the material at the base of the tail is particularly thick and rich in phosphate. Many small spherical structures are also present in this portion, which upon further preparation were revealed to be composed of calcium carbonate. These chemicals suggest that the black material was formed as a product of the specimen's proteins decaying in a warm, stagnant, and acidic environment. As in Macrocnemus, the concentration of this material at the base of the tail suggests that the specimen had a quite noticeable amount of muscle behind its hips. Though this interpretation is not wholly consistent with its proposed neck biomechanics, more recent arguments have supported the idea that Tanystropheus was fully capable of movement on land. Renesto (2005) supported this type of lifestyle as well. Renesto and Franco Saller's 2018 follow-up to Renesto (2005) offered more information on the reconstructed musculature of Tanystropheus. This study determined that the first few tail vertebrae of Tanystropheus would have housed powerful tendons and ligaments that would have made the body more stiff, keeping the belly off the ground and preventing the neck from pulling the body over.
Aquatic capabilities
Tschanz (1986, 1988) suggested that Tanystropheus lacked the musculature to raise its neck above the ground, and that it was probably completely aquatic, swimming by undulating its body and tail side-to-side like a snake or crocodile.