Tanystropheus

Source: Wikipedia, the free encyclopedia.

Tanystropheus
Temporal range: Anisian – early Carnian Possible late Olenekian record
Modelled Tanystropheus skeleton
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Archosauromorpha
Family: Tanystropheidae
Genus: Tanystropheus
Meyer, 1852
Type species
Tanystropheus conspicuus
nomen dubium
Von Meyer, 1855
Other species
  • T. antiquus? Von Huene, 1907-1908
  • T. longobardicus (Bassani, 1886)
  • T. hydroides Spiekman et al., 2020
Synonyms
Genus synonymy
Species synonymy
  • T. biharicus Jurcsák, 1975 (synonym of T. longobardicus?)
  • T. haasi Rieppel, 2001 (nomen dubium)
  • T. meridensis Wild, 1980 (synonym of T. longobardicus)

Tanystropheus (

prolacertiforms
".

Tanystropheus contains at least two valid species as well as fossils which cannot be referred to a specific species. The

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.

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 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).[2] The oldest putative fossils belong to "T. antiquus", a European species from the latest part of the Early Triassic (late Olenekian stage). T. antiquus had a proportionally shorter neck than other Tanystropheus species, so some paleontologists consider that T. antiquus deserves a separate genus, Protanystropheus.

The lifestyle of Tanystropheus has been the subject of much debate.[3] Tanystropheus is unknown from drier environments and its neck is rather stiff and ungainly, suggesting a reliance on water. Conversely, the limbs and tail lack most adaptations for swimming and closely resemble their equivalents in terrestrial 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 been a fatal hindrance to terrestrial locomotion. 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 ambush predator: the narrow subtriangular skull of T. longobardicus is supplied with three-cusped teeth suited for holding onto slippery prey, while the broader skull of T. hydroides bears an interlocking set of large curved fangs similar to the fully aquatic plesiosaurs.

History and species

Monte San Giorgio species

The destroyed holotype of Tanystropheus longobardicus, misinterpreted as a long-tailed pterosaur ("Tribelesodon") until the late 1920s. Fossil (left) and 1923 restoration by Franz Nopcsa (right).

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.[4] In 1886, Francesco Bassani interpreted the unusual tricuspid fossil as a pterosaur, which he named Tribelesodon longobardicus.[5][6] The holotype specimen of Tribelesodon longobardicus was stored in the Museo Civico di Storia Naturale di Milano (Natural History Museum of Milan), and was destroyed by allied bombing of Milan in World War II.[6]

Excavations by

neotype of the species.[6]

Well-preserved T. longobardicus fossils continue to be recovered from Monte San Giorgio up to the present day. Fossils from the mountain are primarily stored at the rebuilt Museo Civico di Storia Naturale di Milano (MSNM), the Paleontological Museum of Zürich (PIMUZ), and the Museo Cantonale di Scienze Naturali di Lugano (MCSN).[6] Rupert Wild reviewed and redescribed all specimens known at the time via several large monographs in 1973/4 and 1980. In 2005, Silvio Renesto described a T. longobardicus specimen from Switzerland which preserved the impressions of skin and other soft tissue.[8] Five new MSNM specimens of T. longobardicus were described by Stefania Nosotti in 2007, allowing for a more comprehensive view of the species' anatomy.[9]

A small but well-preserved skull and neck, specimen PIMUZ T 3901, was found in the slightly younger

junior synonym of T. longobardicus.[10][6] A 2019 revision of Tanystropheus found that T. longobardicus and T. antiquus were the only valid species in the genus.[6]

Tanystropheus specimens from Monte San Giorgio have long been segregated into two morphotypes based on their tooth structure.

Hydra of Greek mythology), while the smaller tricuspid morphotype retains the name T. longobardicus.[11]

Polish and German species

Type vertebrae of "Tanystropheus conspicuus", described in 1855

The first Tanystropheus specimens to be described were found in the mid-19th century. They included eight large vertebrae from the Upper

Lower Keuper of Poland. These geological units occupy part of the Middle Triassic, from the latest Anisian to middle Ladinian stages.[6] Though the fossils were initially given the name Macroscelosaurus by Count Georg Zu Münster, the publication containing this name is lost and its genus is considered a nomen oblitum. In 1855, Hermann von Meyer supplied the name Tanystropheus conspicuus, the type species of Tanystropheus, to the fossils.[12] They were later regarded as Tanystropheus fossils undiagnostic relative to other species, rendering T. conspicuus a nomen dubium possibly synonymous with T. hydroides.[6][13]

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.[14]

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.[15][6]

One of Von Huene's species appears to be valid: T. antiquus, from the Gogolin Formation of Poland, was based on cervical vertebrae which were proportionally shorter than those of other Tanystropheus species. Long considered destroyed in World War II, several T. antiquus fossils were rediscovered in the late 2010s. The proportions of T. antiquus fossils are easily distinguishable, and it is currently considered a valid species of archosauromorph,[6] though its referral to the genus Tanystropheus has been questioned.[16][17] 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.[18][6]

Other Tanystropheus fossils

In the 1880s, E.D. Cope named three supposed new Tanystropheus species (T. bauri, T. willistoni, and T. longicollis) from the Late Triassic Chinle Formation in New Mexico. However, these fossils were later determined to be tail vertebrae belonging to theropod dinosaurs, which were named under the new genus Coelophysis.[6] Authentic Tanystropheus specimens from the Makhtesh Ramon in Israel were described as a new species, T. haasi, in 2001.[19] 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.[20] 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.[21][6] Tanystropheus vertebrae have also been found in the Villány Mountains of Hungary.[22]

The most well-preserved Tanystropheus fossils outside of Monte San Giorgio come from the Guizhou province of China, as described by Li (2007)[23] and Rieppel (2010).[2] They are also among the youngest and easternmost fossils in the genus, hailing from the upper Ladinian or lower Carnian Zhuganpo Formation. Although the postcrania is complete and indistinguishable from the fossils of Monte San Giorgio, no skull material is preserved, and their younger age precludes unambiguous placement into any Tanystropheus species. The Chinese material includes a large morphotype (T. hydroides?) specimen, GMPKU-P-1527, and an indeterminate juvenile skeleton, IVPP V 14472.[2]

Indeterminate Tanystropheus remains are also known from the Jilh Formation of Saudi Arabia and various Anisian-Ladinian sites in Spain, France, Italy, and Switzerland.[6] The youngest Tanystropheus fossil in Europe is a vertebra from the lower Carnian Fusea site in Friuli, Italy.[24][6] In 2015, a large Tanystropheus cervical vertebra was described from the Economy Member of the Wolfville Formation, in the Bay of Fundy of Nova Scotia, Canada.[25][6] The Wolfville Formation spans the Anisian to Carnian stages, and the Economy Member is likely Middle Triassic (Anisian-Ladinian) in age. It is a rare example of predominantly freshwater strata preserving Tanystropheus fossils.[26] Tanystropheus-like tanystropheid fossils are known from another freshwater formation in North America: the Anisian-age Moenkopi Formation of Arizona and New Mexico.[27]

Several new

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,[16] though a few studies continued to retain that species within Tanystropheus.[6] Tanystropheus fossai, from the Norian-age Argillite di Riva di Solto in Italy, was given its own genus Sclerostropheus in 2019.[6]

Anatomy

Size comparison between T. 'conspicuus', T. hydroides (PIMUZ T 2793), and T. longobardicus (MSNM V 3730)

Tanystropheus was one of the longest known non-archosauriform archosauromorphs. Vertebrae referred to "T. conspicuus" may correspond to an animal up to five or six meters (16.4 to 20 feet) in length.[6] T. hydroides was around the same size, with the largest specimens at an estimated length of 5.25 meters (17.2 feet).[11] T. longobardicus was significantly smaller, with an absolute maximum size of two meters (6.6 feet).[13][17] Despite the large size of some Tanystropheus species, the animal was lightly built. One mass estimate used crocodiles as a density guideline for a 3.6 meter (11.8 feet)-long model of a Tanystropheus skeleton. For a Tanystropheus individual of that length, the weight estimate varied between 32.9 kg (72.5 lbs) and 74.8 kg (164.9 lbs), depending on the volume estimation method. This was significantly lighter than crocodiles of the same length, and more similar to large lizards.[29]

Skull of Tanystropheus longobardicus

PIMUZ T 3901, a specimen of Tanystropheus longobardicus formerly described as "Tanystropheus meridensis". Skull and partial neck (top) and a closer view of the skull (bottom).

The skull of Tanystropheus longobardicus is roughly triangular when seen from the side and top, narrowing towards the snout.

nares (nostril holes).[9][6][13] The nasals (bones at the top edge of the snout) are poorly known, but were likely narrow and flat.[9] A 2020 reinvestigation revealed that the front part of the nasals and the inner spur of the premaxillae are too short to keep the nares divided. This leaves a single central narial opening for the nostrils, opening upwards. An undivided naris is seen in few other archosauromorphs, namely rhynchosaurs, most allokotosaurs, modern crocodilians, and Teyujagua.[11][13]

The maxilla is triangular, reaching its maximum height at mid-length and tapering to the front and rear.[9] There are up to 14[9] or 15[6] teeth in the maxilla, though some individuals have fewer.[9] T. longobardicus is a reptile with heterodont dentition, meaning that it had more than one type of tooth shape. In contrast to the simple fang-like premaxillary teeth, most or all of the maxillary teeth have a distinctive tricuspid shape, with the crown split into three stout triangular cusps (points). The cusps are arranged in a line from front-to-back, with the central cusp larger than the other two cusps.[9] Among Triassic reptiles, early pterosaurs such as Eudimorphodon developed an equivalent tooth shape, and tricuspid teeth can also be found in a few modern lizard species.[30][31] 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.[9][6]

The front edge of each

infratemporal fenestra (lower skull hole behind the eye) was incomplete and open from below.[13] The postorbital bone, which links the jugal to the top of the skull, was tall and roughly boomerang-shaped, though poor preservation obscures some details.[11] The squamosal bone, which extends behind the postorbital, is also poorly known in T. longobardicus, and many supposed squamosal fossils in the species have been reinterpreted as displaced postorbitals.[11][13] The quadrate bone, which forms the rear edge of the skull and upper half of the jaw joint, is wide and tall. It has a strong lateral crest and a low pterygoid ramus (a vertical internal plate, articulating with the pterygoid bone in the roof of the mouth).[9] No fossils of T. longobardicus preserve a quadratojugal, a bone which normally lies along the quadrate at the rear lower corner of the skull. Nevertheless, a quadratojugal was likely present in the species, since it occurs in T. hydroides and nearly every other early archosauromorph.[11][13]

neotype
PIMUZ T 2791 (top) and MSNM BES SC 1018 (bottom).

The paired

pineal foramen[6][13] (sometimes called the parietal foramen),[9] is present at the midline of the skull between the front part of each parietal. When seen from below, a pair of curved crests along the frontals and parietals mark the edge of the forebrain, as defined by a bulbous central hollow.[9]

The eye was supported by more than 10 rectangular ossicles (tiny plate-like bones) connecting into a

braincase and palate (bony roof of the mouth) are known for T. longobardicus. The scant available evidence suggests that these regions of the skull are rather unspecialized in this species.[13] The vomers (front components of the palate) are narrow and dotted with at least nine tiny teeth. The succeeding palatine and pterygoid bones are also supplied with rows of teeth: up to six relatively large teeth in the former and at least 12 small teeth in the latter.[9][6] Teeth on the vomers, palatines, and pterygoids are the norm for early archosauromorphs and reptiles as a whole.[6][13]

The

coronoid bone could be present in front of the surangular, evidence is ambiguous at best for all Tanystropheus species.[9][13] A sheathe-like bone, the angular, is well-exposed under the dentary and surangular, though sutures between these bones are difficult to interpret with certainty.[13] The joint at the back of the jaw lies on the articular, a lumpy rectangular bone which is floored and reinforced by a similar bone: the prearticular. In Tanystropheus species with known skull material, both the articular and prearticular contribute equally to a segment of the jaw extending back beyond the level of the jaw joint. This projection, known as a retroarticular process, is enlarged[6] to a similar degree to that of early rhynchosaurs.[13]

Skull of Tanystropheus hydroides

The skull of PIMUZ T 2790, the holotype of Tanystropheus hydroides. Digital reconstruction in lateral views (top); dorsal, ventral, and occipital views (left middle); line diagram in left lateral, dorsal, and ventral views (right middle); 3D printed model (bottom).

The skull of Tanystropheus hydroides is broader and flatter than that of T. longobardicus. The first five of six teeth in the premaxilla are very large and fang-like, forming an interlocking "fish trap" similar to

supratemporal fenestrae (upper skull holes behind the eye) are wide and semi-triangular, exposed almost entirely from above.[13] The postorbital has large and blocky ventral and medial processes (lower and inward branches), which meet at a sharper angle than in any other early archosauromorph. The jugal, conversely, is basically indistinguishable from that of T. longobardicus. The squamosal is deep and rectangular when viewed from the side, with little differentiation between the tall suture with the postorbital and the small suture with the quadratojugal. As a result, most of the posterior skull is clustered together, and the infratemporal fenestra is reduced to a small diagonal hole. The quadratojugal is a curved sliver of bone which twists back alongside the quadrate. Relative to T. longobardicus, the quadrate has a larger pterygoid ramus and a strongly hooked projection at its upper extent.[11][13]

The palate of T. hydroides has several unique traits.[6][11][13] The vomers are wide and tongue-shaped, each hosting a single row of 15 relatively large curved teeth along the outer edge of the bone, adjacent to the elongated choanae (internal openings of the nasal cavity).[6][11][13] Most other archosauromorphs, T. longobardicus included, have restricted vomers with rows of minuscule teeth. The rest of the palate is completely toothless in T. hydroides, even the palatines and pterygoids, which bear tooth rows in most early archosauromorphs.[6][11][13] The pterygoids are also unusual for their broad palatal ramus (front plate) and a loose, strongly overlapping connection to the ectopterygoids (linking bones between the pterygoid and maxilla). The epipterygoids (vertical bones in front of the braincase) are tall and flattened from the side.[13]

Digital reconstruction of the braincase of PIMUZ T 2790. Basioccipital (blue), parabasisphenoid (red), and composite bone (yellow).

T. hydroides is a rare example of an early archosauromorph with a three-dimensionally preserved braincase.

supraoccipitals, which were presumably fused together as a continuous surface sloping smoothly down to the foramen magnum.[13]

PIMUZ T 2793, a lower jaw and associated vertebrae of T. hydroides

In the lower jaw, the dentaries meet each other at a robust symphysis with an interdigitating suture.[13] The front end of the dentary hosts a prominent keel on its lower edge, a unique trait of the species.[6][11][13] There are at least 18 dentary teeth; the first three are by far the largest teeth in the skull, forming the lower half of the interlocking "fish trap" with the premaxilla. Most other teeth in the dentary are small, with the exception of the tenth tooth, which juts up to pierce the maxilla. The remainder of the jaw contains the same set of bones as in T. longobardicus, but some details differ in T. hydroides.[13] For example, the splenial is plate-like and covers a larger portion of the internal dentary than in T. longobardicus. In addition, the rear of the dentary overlaps a large portion of the surangular, rather than the surangular acting as the overlapping bone where they meet. The surangular internally bears a large fossa for the jaw's adductor (vertical biting) muscles, and a prominent surangular foramen is positioned in front of the jaw joint.[13]

Neck

Atlas-axis complex of PIMUZ T 2790

The most recognisable feature of Tanystropheus is its hyperelongate neck, equivalent to the combined length of the body and tail.

postzygophyses (rear articular plates) are separated by a broad trough and support pointed epipophyses (additional projections).[13]

Skeletal diagram of T. hydroides (top) and mounted model skeleton (bottom) of Tanystropheus. The modeled skeleton is reconstructed from T. longobardicus and T. hydroides material

The third to eleventh cervicals are hyperelongate in T. longobardicus and T. hydroides, ranging from three to 15 times longer than tall. They are somewhat less elongated in T. antiquus, less than 6 times longer than tall. The cervicals gradually increase in size and proportional length, with the ninth cervical typically being the largest vertebra in the skeleton.[6] In general structure, the elongated cervicals resemble the axial pleurocentrum. However, the axis also has a keel on its underside and an incomplete neural canal, unlike its immediate successors.[13] In the rest of the cervicals, all but the front of each neural spine is so low that it is barely noticeable as a thin ridge. The zygapophyses are closely set and tightly connected between vertebrae. The epipophyses develop into hooked spurs. The cervicals are also compressed from the side, so they are taller than wide. Many specimens have a longitudinal lamina (ridge) on the side of each cervical. Ventral keels return to vertebrae in the rear half of the neck.[9][6]

All cervicals, except potentially the atlas, connected to holocephalous (single-headed) cervical ribs via facets at their front lower corner. Each cervical rib bears a short stalk connecting to two spurs running under and parallel to the vertebrae. The forward-projecting spurs were short and stubby, while the rear-projecting spurs were extremely narrow and elongated, up to three times longer than their respective vertebrae. This bundle of rod-like bones running along the neck afforded a large degree of rigidity.[8][9][2]

The 12th cervical and its corresponding ribs, though still longer than tall, are notably shorter (from front-to-back) than their predecessors. The 12th cervical has a prominent neural spine and robust zygapophyses, also unlike its predecessors. The 13th vertebra has long been assumed to be the first dorsal (torso) vertebra. This was justified by its general stout shape and supposedly dichocephalous (two-headed) rib facets, unlike the cervicals. However, specimen GMPKU-P-1527 has shown that the 13th vertebra's rib simply has a single wide articulation and an unconnected forward branch, more similar to the cervical ribs than the dorsal ribs.[2]

Torso and tail

PIMUZ T 2817, a large morphotype (T. hydroides) specimen missing only the skull and a portion of the neck

There are 12

gastralia extend along the belly, each gastral element represented by a pair of segmented rods which intermingle at the midline.[9][2]

The two

caudal vertebrae.[9] The first few caudals are large, with closely interlinked zygapophyses and widely projecting pleurapophyses (a term for transverse processes lacking ribs). The length of the pleurapophyses decreases until they disappear between the eighth and thirteenth caudal. The height of the neural spines also decreases gradually down the tail.[8][9][2] A row of long chevrons is present under a short portion of the tail, though not immediately behind the hips.[2]

Shoulder and forelimbs

Shoulder region and forearm of PIMUZ T 2817

The pectoral girdle (shoulder girdle) has a fairly standard form shared with other tanystropheids. The clavicles (collarbones) were curved and slightly twisted rods.[9][2] They lie along the front edge of the interclavicle, a plate-like bone at the center of the chest with a rhombic (broad, diamond-shaped) front region followed by a long stalk at the rear.[6] The interclavicle is rarely preserved and its connections to the rest of the pectoral girdle are mostly inferred from Macrocnemus.[33] 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).[8][9][2]

The

ulnare, radiale, and two distal carpals. The ulnare and radiale are large and cuboid, enclosing a small foramen (gap) between them. The larger outer distal carpal connects to metacarpals III and IV, while the much smaller inner distal carpal connects to metacarpals II and III. Metacarpals III and IV are the largest bones in the hand, followed closely by metacarpal II. Metacarpals I and V are both short. The hand's phalangeal formula (joints per finger) is 2-3-4-4-3. The terminal phalanges (fingertips) may have formed thick, blunt claws.[9][2][6]

Hip and hindlimbs

Hind foot of PIMUZ T 2817

The components of the pelvis (hip) are proportionally small, though their shape is unremarkable relative to other tanystropheids.[9] The ilium (upper hip blade) is low and extends to a tapered point at the rear. The pubis (lower front hip blade) is vertically oriented, with a small but distinct obturator foramen and a concave rear edge. The lower front tip of the large, fan-shaped ischium (lower rear hip blade) converges towards the pubis, but does not contact it. The large oval-shaped gap between the pubis and ischium is known as the thyroid foramen.[8][2]

Two pairs of large, curved bones, known as heterotopic ossifications[8][2][6] or postcloacal bones,[34] 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.[8][2][6] These bones are possibly sexually dimorphic, and have also been reported in the small American tanystropheid Tanytrachelos. Heterotopic ossifications may be linked to reproductive biology, supporting reproductive organs (if they belong to males) or an egg pouch (if they belong to females).[35][8]

The hindlimbs are significantly larger than the forelimbs, though similar in overall structure and proportions. The femur (thigh bone) is long, slender, and sigmoid (curved at both ends). It has a longitudinal muscle crest for muscle attachment (the internal trochanter) on its underside, and it contacts the acetabulum (hip socket) at a broad smooth joint. The tibia and fibula (shin bones) are straight, with the former much thicker and more expanded at the knee. The large proximal tarsals (ankle or heel bones contacting the shin) consist of a rounded calcaneum and a blocky astragalus, which meet each other along a straight or shallowly indented contact in most specimens.[9][2] Like most non-aquatic reptiles, a set of small pebble-shaped distal tarsals are present between the proximal tarsals and the foot bones. Tanystropheus has a reduced number of distal tarsals: only a small fourth distal tarsal and a minuscule third distal tarsal.[9][6] There are five closely appressed metatarsals (foot bones), with the fourth and third being the longest. Though the first four metatarsals are slender and similar in length, the fifth (outermost) is very stout and subtly hooked, slotting into the ankle along a smooth joint.[8][9][2] The estimated phalangeal formula (joints per toe) is 2-3-4-5-4. The first phalange of the fifth toe was very long, filling a metatarsal-like role as seen in other tanystropheids.[8][6]

Classification

Historical interpretations (1920s-1980s)

protorosaur
". Some 20th-century paleontologists classified Tanystropheus and Macronemus as Triassic protorosaurs.

Knowledge on the anatomy of Tanystropheus was transformed by Bernhard Peyer's discoveries in the 1920s and 1930s, but its relationship to other reptiles remained enigmatic for much of the 20th century. Most paleontologists (including modern authorities) agree that Tanystropheus was closely related to Macrocnemus, a smaller and less specialized reptile found in the same geological strata.[36][37][17] Beyond this conclusion, Peyer initially suggested that Tanystropheus was related to other long-necked Triassic reptiles. Sauropterygians such as plesiosaurs and nothosaurs were one possibility, and another was the fragmentary German reptile Trachelosaurus.[7] Later, Peyer classified Tanystropheus and Macrocnemus closer to "protorosaurs", a term initially used for Permian reptiles such as Protorosaurus and Araeoscelis.[36]

In the early and mid-20th century, it was commonplace for Permian and Triassic reptiles of uncertain affinity to intermingle together in classification schemes. Names such as "

Prolacertiformes".[42]

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 "

upper temporal fenestra) related to sauropterygians,[47][38] though later accounts admitted that Euryapsida was likely polyphyletic, with its members lacking a common ancestor.[40][48]

In 1975, a paper by South African paleontologist C.E. Gow argued that none of these hypotheses were entirely correct.[49] 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.[49] Dinosaurs are among the most famous subset of archosaurs, as are modern crocodilians and their prehistoric ancestors.[37] Several newly discovered "prolacertiforms", including Tanystropheus-,[50] Protorosaurus-,[51] and Prolacerta-like species,[52] 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)

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

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.[53][54] 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.[55]

A series of phylogenetic analyses in the late 1980s and 1990s strongly supported the proposal of Gow (1975).[53][56][52][57][58] 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.[59] 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.[56]

As a "prolacertiform", Tanystropheus is typically considered the

sister taxon to Tanytrachelos, a much smaller tanystropheid from Virginia. Another small tanystropheid, Cosesaurus from Spain, is allied with the Tanystropheus + Tanytrachelos clade in many analyses of the 1980s and 1990s.[56][57][52] Within Archosauromorpha, "prolacertiforms" are joined by several other groups.[37] The clade Archosauriformes is a diverse archosauromorph subset including crown group archosaurs and their predatory close relatives such as Euparkeria and Proterosuchus. Stocky Triassic herbivores like rhynchosaurs, Trilophosaurus, and azendohsaurids[60] additionally qualify as archosauromorphs.[37] The bizarre chameleon-like drepanosaurs were also included by many analyses,[56][61][58] though more recently they have been reinterpreted as a more basal type of reptile unrelated to Archosauromorpha.[62]

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:[58]

Sauria

Recent studies and the rejection of "prolacertiform" monophyly (2000s-present)

Starting with Dilkes (1998), many phylogenetic analyses began to recover Prolacerta in a position close to archosauriforms and away from other "prolacertiforms".[58] In addition, a 2009 redescription of Protorosaurus shifted it away from Tanystropheus and close to the base of Archosauromorpha.[63] 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.[64][63][37]

The family Tanystropheidae has come to succeed those older names, acting as a monophyletic clade oriented around Tanystropheus. Tanystropheidae hosts a growing list of former "protorosaurs" with closer affinities to Tanystropheus than to Prolacerta, Protorosaurus, or other major archosauromorph groups. Tanystropheus is well-nested within Tanystropheidae, sometimes as the sister taxon to Amotosaurus.[65][60][37] Macrocnemus is most commonly the basal-most (first diverging) tanystropheid.[65][60][37][17]

A set of phylogenetic analyses by Spiekman et al. (2021) attempted to tackle the question of "protorosaur" relationships using an expanded and updated sample of archosauromorph species described over the past few decades. Tanystropheus was split into five taxonomic units in this study: T. longobardicus, T. hydroides, T. "conspicuus", "T. antiquus" (

discrete characters and character state ordering, while the other included these settings. In some analyses, "wildcard" taxa with inconsistent positions were excluded to improve resolution.[17]

Regardless of the setting, T. longobardicus, T. hydroides, T. "conspicuus", and GMPKU P1527 always formed a clade, though the latter two were excluded from some analyses as "wildcards". Under some settings (but not the most stable analysis), another tanystropheid was added to this clade:

Dinocephalosauridae, outside of Tanystropheidae. Sclerostropheus fossai, another species formerly referred to Tanystropheus, was an unpredictable "wildcard", sometimes placed within Dinocephalosauridae and other times within Tanystropheidae.[17]

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.[17]

Archosauromorpha
Protorosaurus

Prolacerta

Jesairosaurus

Dinocephalosauridae

Macrocnemus bassanii

Macrocnemus fuyuanensis

Macrocnemus obristi

Langobardisaurus

Fuyuansaurus

AMNH FARB 7206 (an unnamed Tanytrachelos-like tanystropheid from New Jersey)

Tanytrachelos

Tanystropheus hydroides

GMPKU P 1527 (T. cf. hydroides)

Tanystropheus longobardicus

Crocopoda

Paleoecology

Diet

plesiosaurs. This was likely an adaptation for catching aquatic prey. Additionally, fish scales and hooklets from cephalopod tentacles have been found in the stomach region of some specimens, further support for a piscivorous diet.[9][11]

Small specimens from Monte San Giorgio (T. longobardicus) are noted to possess tricuspid teeth at the back of the jaw. This shape is unorthodox and uncommon among extinct or living reptiles. Wild (1973/1974) considered these three-cusped teeth to be an adaptation for gripping insects. Cox (1985) noted that marine iguanas, which feed on algae, also have three-cusped teeth. As a result, he attributed the same preferences to Tanystropheus. Taylor (1989) rejected both of these hypotheses, as he interpreted the neck of Tanystropheus to be too inflexible for the animal to be successful at either lifestyle.[9]

The most likely function of tricuspid teeth, as explained by Nosotti (2007), was that they assisted the piscivorous diet of the reptile by helping to grip slippery prey such as fish or squid. Several modern species of seals, such as the hooded seal and crabeater seal, also have multi-cusped teeth which assist their diet to a similar effect.[9] Similar teeth have also been found in the pterosaur Eudimorphodon and the fellow tanystropheid Langobardisaurus, both of which are considered piscivores. Crustaceans and other soft invertebrates are also plausible food items for Tanystropheus longobardicus. Larger individuals (Tanystropheus hydroides) lack three-cusped teeth, instead possessing typical conical fangs along the entire rim of the mouth. This difference in dentition indicates a degree of niche partitioning, with T. hydroides preferring larger and more active prey than T. longobardicus.[11]

Predation

PIMUZ T 2819, a T. hydroides specimen which was decapitated by a larger predator

While long necks were a successful evolutionary strategy for many marine reptile clades during the Mesozoic, they also increased the animals' vulnerability to predation. Spiekman and Mujal (2023) investigated two Tanystropheus fossils (PIMUZ T 2819 and PIMUZ T 3901), each consisting solely of a skull attached to an articulated partial neck. PIMUZ T 2819 (a large specimen of T. hydroides) is preserved up to cervical vertebra 10, which is splintered by punctures and scoring. The shape of the marks indicate that the neck was severed in two rapid bites by a predator attacking from above and behind. A similar predation attempt occurred against PIMUZ T 3901 (the Meride Limestone specimen of T. longobardicus), which was bitten at cervical 5 and severed at cervical 7. The authors further suggested that since the decapitation occurred in the mid-section of the neck, this was likely an optimal target due to its distance from the head and the muscular base of the neck. While many contemporary marine reptiles were capable of attacking PIMUZ T 3901, only the largest predators of the Besano Formation could have attacked PIMUZ T 2819.

Cymbospondylus buchseri, and Helveticosaurus zollingeri are all candidates for the latter case.[67]

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

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.[13]

Fragments of rod-like hyobranchial elements (throat bones) have been found in fossils of both T. hydroides and T. longobardicus. These hyobranchials are very slender and disarticulated, without a bony corpus (thickened "body" of the

Suction feeding is rejected, since it is correlated with a more robust and integrated hyoid apparatus.[13]

Growth and development

metabolic rate more similar to lizards than to archosauriforms.[34]

Respiration

As neck length increases, so does tracheal volume, which imposes a biological limitation on breathing. Every time the animal inhales, a significant portion of oxygenated air (so-called dead space volume) fails to pass fully through the trachea and reach the lungs. Many long-necked animals have adaptations meant to overcome this limitation. For example, giraffes have a narrow trachea and infrequent breathing, which reduces the dead space volume. Sauropod dinosaurs supplement their trachea with air sacs that allow for greater air movement through the respiratory system. Birds utilize both air sacs and infrequent breathing. Tanystropheus would need to rely on exceptionally specialized lungs which exceed any allometric predictions based on modern reptiles. In a compromise between energy usage and minimizing dead space volume, the ideal trachea width for Tanystropheus is around 1 cm (0.4 inches), for a neck 1.7 meters (5.6 feet) in length. During periods of high activity, the only lung structure capable of meeting oxygen needs is a multicameral lung (partitioned into multiple smaller chambers) with unidirectional air flow and infrequent breathing. This type of respiratory system is seen in modern archosaurs and turtles. In any case, Tanystropheus's lung capacity was too small for frequent activity or life at higher altitudes. This supports its proposed ecology as coastal ambush predator.[29]

Soft tissue

A specimen described by Renesto in 2005 displayed an unusual "black material" around the rear part of the body, with smaller patches at the middle of the back and tail. Although most of the material was amorphous, the portion just in front of the hip seemingly preserved scale impressions, indicating that the black material was the remnants of soft tissue. The scales seem to be semi-rectangular and do not overlap with each other, similar to the integument reported in a juvenile Macrocnemus described in 2002.[68] 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.[8]

Brain and inner ear

Digital endocast of PIMUZ T 2790, showing the brain cavity (blue), inner ear (red), and nerve canals (yellow)

Impressions on the frontal bones of Tanystropheus longobardicus fossils indicate that that species at least had a bulbous

olfactory bulbs.[9] The complete braincase of Tanystropheus hydroides specimen PIMUZ T 2790 allowed for a partial reconstruction of the brain cavity and inner ear via a digital endocast. The flocculus is large and broad and leads forward to the rest of the cerebellum, which is narrowest between the endosseus labyrinth (inner ear canals). A large flocculus may relate to greater head and eye stabilization, though evidence is inconclusive. Long-necked sauropods show a reduction of the flocculus and there is no clear correlation between flocculus size and function in modern mammals and birds. Like other reptiles, Tanystropheus has three semicircular canals ringing out of the inner ear. Tanystropheus likely stayed in shallow waters or on land, since its semicircular canals are much thinner than those of deep-diving seabirds. The anterior semicircular canal, which curves up and around the flocculus, is enlarged. The posterior semicircular canal (which slopes backwards and outwards from the brain) is smaller, as is the lateral semicircular canal (which arches outwards). The lateral semicircular canal is nearly horizontal in orientation, which possibly relates to a horizontal head posture. There is also a long straight cochlear duct extending outwards, and a long cochlear duct typically indicates good hearing ability in living reptiles.[13]

Terrestrial capabilities

Life reconstruction of T. longobardicus hunting from the seashore

The lifestyle of Tanystropheus is controversial, with different studies favoring a terrestrial or aquatic lifestyle for the animal. Major studies on Tanystropheus anatomy and ecology by Rupert Wild (1973/1974, 1980) argued that it was an active terrestrial predator, keeping its head held high with an S-shaped flexion.[43] 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.[8][69][70][71]

Renesto (2005) argued that the neck of Tanystropheus was lighter than previously suggested, and that the entire front half of the body was more lightly built than the more robust and muscular rear half.

ossified tendons of many large dinosaurs, transmitting forces from the weight of the head and neck down to the pectoral girdle, as well as providing passive support by limiting dorsoventral (vertical) flexion.[72][8] Unlike ossified tendons, the cervical ribs of Tanystropheus are dense and fully ossified throughout the animal's lifetime, so its neck was even more inflexible than that of dinosaurs.[34]

A pair of 2015 blog posts by paleoartist Mark Witton estimated that the neck made up only 20% of the entire animal's mass, due to its light and hollow vertebrae. By comparison, in pterosaurs of the family Azhdarchidae, which were clearly large terrestrial predators, the neck and head made up almost 50% of their mass. Witton proposed that Tanystropheus would have hunted prey from the seashore, akin to a heron.[69][70] Renesto (2005) supported this type of lifestyle as well.[8] A later published estimate argued that the neck comprised about 30 to 43% of the body mass.[29] Terrestrial or semi-terrestrial habits are supported by taphonomic evidence: Tanystropheus specimens preserved at Monte San Giorgio have high completeness (most bones are present in an average fossil) but variable articulation (bones are not always preserved in life position). This is similar to Macrocnemus (which was terrestrial) and opposite the pattern seen in Serpianosaurus (which was fully aquatic).[71] 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.[73]

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.[72] This interpretation has been contradicted by later studies,[8] although Tanystropheus may have still spent a large portion of its life in shallow water.[73][11][13]

Renesto (2005) argued that Tanystropheus lacked clear adaptations for underwater swimming to the same degree as most other aquatic reptiles. The tail of Tanystropheus was compressed vertically (from top-to-bottom) at the base and thinned towards the tip, so it would not have been useful as a fin for lateral (side-to-side) movement. The long neck and short front limbs shifted the center of mass back to the long hind limbs, which would have made four-limbed swimming inefficient and unstable if that was the preferred form of locomotion. He additionally claimed that thrusting with only the hind limbs, as in swimming frogs, was an inefficient form of locomotion for a large animal such as Tanystropheus.[8]

Life restoration of Tanystropheus in the water, from Renesto and Saller (2018)
Reconstruction of the major muscles between the legs, hip, and tail in Tanystropheus, from Renesto and Saller (2018)

Contrary to earlier arguments, Renesto and Saller (2018) found some evidence that Tanstropheus was adapted for an unusual style of swimming.

ichnogenus (trackway fossil) Gwyneddichnium, which was likely created by small tanystropheids such as Tanytrachelos. Some Gwyneddichnium tracks seem to represent a succession of paired sprawling footprints from the hind limbs, without any hand prints. These tracks may have been created by the same form of movement which Renesto and Saller (2018) hypothesized as the preferred method of swimming in Tanystropheus.[73]

Nevertheless,

lateral undulation cannot be disregarded as a potential swimming style; vertebrae near the hips have extended transverse processes, which are associated with powerful undulating tail muscles in reptiles such as crocodilians. Tail movements may be more effective for swimming than paddling or thrusting with the hindlimbs, since the foot bones of Tanystropheus are narrowly bundled together with little room for webbing.[13]

The skull of Tanystropheus shows additional support for a semiaquatic habits: both T. hydroides and T. longobardicus have large undivided nares positioned on the upper surface of the snout, a location consistent with this lifestyle in other animals.

References

  1. ^ Elbein, Asher (12 August 2020). "Making Sense of 'One of the Most Baffling Animals That Ever Lived' - Important mysteries have been solved about a reptile with a giraffe-like neck that hunted prey 242 million years ago". The New York Times. Retrieved 14 August 2020.
  2. ^
    S2CID 86315078
    .
  3. .
  4. ^ Tanystropheus. Vertebrate Palaeontology at Milano University. Retrieved 2007-02-19.
  5. S2CID 131644821
    .
  6. ^ .
  7. ^ a b Peyer, Bernhard (1931). "Die Triasfauna der Tessiner Kalkalpen II. Tanystropheus longobardicus Bass. sp". Abhandlungen der Schweizerischen Paläontologischen Gesellschaft. 50: 9–110.
  8. ^ a b c d e f g h i j k l m n o p q r s t Renesto, S. (2005). "A new specimen of Tanystropheus (Reptilia, Protorosauria) from the Middle Triassic of Switzerland and the ecology of the genus". Rivista Italiana di Paleontologia e Stratigrafia. 111 (3): 377–394.
  9. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap Nossotti, Stefania (2007). "Tanystropheus longobardicus (Reptilia Protorosauria): Re-interpretations of the anatomy based on new specimens from the Middle Triassic of Besano (Lombardy, northern Italy)". Memorie della Societa Italiana di Scienze Naturali e del Museo Civico di Storia Naturale di Milano. 35 (3).
  10. S2CID 220415208
    .
  11. ^ .
  12. ^ von Meyer, Hermann (1855). "Die Saurier des Muschelkalkes mit Rücksicht auf die Saurier aus buntem Sandstein und Keuper". Zur Fauna der Vorwelt, Zweite Abtheilung. Frankfurt: Heinrich Keller: 1–167.
  13. ^
    PMID 33240633
    .
  14. .
  15. .
  16. ^ .
  17. ^ .
  18. ^ a b Wild, R.; Oosterink, H. (1984). "Tanystropheus (Reptilia: Squamata) aus dem Unteren Muschelkalk von Winterswijk, Holland". Grondboor & Hamer. 38 (5): 142–148.
  19. .
  20. ^ Jurcsák, Tibor (1975). Tanystropheus biharicus n.sp. (Reptilia, Squamata) o nouă specie pentru fauna triasică a României (in Romanian). Vol. 3. Nymphaea. pp. 45–52.
  21. .
  22. .
  23. ^ Chun, Li (2007). "A juvenile Tanystropheus sp. (Protorosauria, Tanystropheidae) from the Middle Triassic of Guizhou, China" (PDF). Vertebrata PalAsiatica (in Chinese). 45 (1): 37–42. Archived from the original (PDF) on 22 February 2017.
  24. .
  25. S2CID 17520371. Archived from the original
    (PDF) on 8 March 2019.
  26. .
  27. .
  28. .
  29. ^ .
  30. .
  31. .
  32. .
  33. .
  34. ^ .
  35. ^ Olsen, Paul E. (1979). "A new aquatic Eosuchian from the Newark Supergroup (Late Triassic–Early Jurassic) of North Carolina and Virginia" (PDF). Postilla. 176: 1–14.
  36. ^ a b Peyer, Bernhard (1937). "Die Triasfauna der Tessiner Kalkalpen XII. Macrocnemus bassanii Nopcsa". Abhandlungen der Schweizerischen Paläontologischen Gesellschaft. 54: 1–87.
  37. ^
    PMID 27162705
    .
  38. ^ .
  39. ^ .
  40. ^ .
  41. .
  42. .
  43. ^ a b Wild, R. 1973. Tanystropheus longbardicus (Bassani) (Neue Egerbnisse). in Kuhn-Schnyder, E., Peyer, B. (eds) — Triasfauna der Tessiner Kalkalpen XXIII. Schweiz. Paleont. Abh. Vol. 95 Basel, Germany.
  44. ^ Emil, Kuhn-Schnyder (1954). "Über die Herkunft der Eidechsen". Endeavor (in German). 13: 215–221.
  45. S2CID 129660030
    .
  46. .
  47. ^ Colbert, Edwin H. (1951). The dinosaur book: the ruling reptiles and their relatives. New York: McGraw-Hill.
  48. S2CID 5391625
    .
  49. ^ .
  50. ^ Olsen, Paul E. (1979). "A new aquatic Eosuchian from the Newark Supergroup (Late Triassic–Early Jurassic) of North Carolina and Virginia" (PDF). Postilla. 176: 1–14.
  51. .
  52. ^ a b c Benton, Michael J.; Allen, Jackie L. (November 1997). "Boreopricea from the Lower Triassic of Russia, and the relationships of the prolacertiform reptiles" (PDF). Palaeontology. 40 (4): 931–953.
  53. ^
    ISSN 0024-4082
    .
  54. .
  55. .
  56. ^ a b c d Evans, Susan E. (1988). "The early history and relationships of the Diapsida". In Benton, M. J. (ed.). The Phylogeny and Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds. Oxford: Clarendon Press. pp. 221–260.
  57. ^
    JSTOR 4523832
    .
  58. ^ .
  59. .
  60. ^ .
  61. .
  62. .
  63. ^ .
  64. .
  65. ^ .
  66. ^ Scheyer et al. (2014): Early Triassic Marine Biotic Recovery: The Predators' Perspective. PLoS ONE https://doi.org/10.1371/journal.pone.0088987
  67. S2CID 259207369
    .
  68. .
  69. ^ a b Witton, Mark (13 November 2015). "Mark Witton.com Blog: The lifestyle of Tanystropheus, part 1: was that neck too heavy for use on land?". Retrieved 23 September 2018.
  70. ^ a b Witton, Mark (11 December 2015). "Mark Witton.com Blog: The lifestyle of Tanystropheus, part 2: coastal fisher or first-day-on-the-job aquatic predator?". Retrieved 23 September 2018.
  71. ^
    S2CID 133762329
    .
  72. ^ a b Tschanz, K. 1988. Allometry and Heterochrony in the Growth of the Neck of Triassic Prolacertiform Reptiles. Paleontology. 31:997–1011.
  73. ^
    ISSN 2039-4942
    .

Bibliography

  • George Olshevsky expands on the history of "P." exogyrarum Archived 2016-04-12 at the Wayback Machine, on the Dinosaur Mailing List
  • Huene, 1902. "Übersicht über die Reptilien der Trias" [Review of the Reptilia of the Triassic]. Geologische und Paläontologische Abhandlungen. 6, 1-84.
  • Fritsch, 1905. "Synopsis der Saurier der böhm. Kreideformation" [Synopsis of the saurians of the Bohemian Cretaceous formation]. Sitzungsberichte der königlich-böhmischen Gesellschaft der Wissenschaften, II Classe. 1905(8), 1–7.

External links