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A new specimen of Tanystropheus (Reptilia Protorosauria) from the Middle Triassic of Switzerland and the ecology of the genus
Abstract
A new specimen of the protorosaurian diapsid reptile Tanystropheus is described. The specimen was collected at the Valle Serrata locality (Switzerland) and is of Ladinian (Middle Triassic) age. Its study elucidates some issues regarding the anatomy of Tanystropheus to be addressed, and allows to suggest hypotheses about its mode of life. In particular, the specimen is the first one in which the skin and other soft tissues can be described. In particular, wide patches of black phosphatic material, filled with small carbonate spherules are preserved, as it occurs in corpses lying in stagnant water due to decomposition of consistent amount of proteins. This suggests that a huge mass of flesh was present in the caudal part of the body, shifting posteriorly the center of mass of the animal and helping in balancing the weight of the neck even if raised off horizontal plane and out of water. In addition, no evidence of caudal autotomy is present in Tanystropheus and the structure of the tail and of the limbs are consistent with a shoreline habitat rather than with a fully aquatic mode of life.
... The morphology of the cervical vertebrae in Tanystropheus is unique, owing to their hyperelongation and reduction of the neural spine. They bear some resemblance only to certain pterosaur vertebrae [9]-no modern anatomical analogues exist. Therefore, it is difficult to interpret how this animal functioned and why its vertebral anatomy was modified to such an immense extent. ...
... The development and evolution of this feature are poorly known. Many biomechanical interpretations have been suggested [2][3][4][9][10][11][12][13][14]; yet, the mystery of the behaviour and habitat of Tanystropheus still remain largely unresolved. ...
... In the past, only some basic morphometric methods have been used to evaluate tanystropheid fossils [3,4,9,11,12]. Herein, we use more sophisticated, two-and three-dimensional geometric morphometric methods (GMMs) to investigate the shape variation in the postaxial cervical vertebrae within Tanystropheidae and other closely related archosauromorphs, to differentiate the morphological subregions in the necks of the studied taxa and to compare them with the results available for both extant and extinct animals. ...
The Triassic radiation of vertebrates saw the emergence of the modern vertebrate groups, as well as numerous extinct animals exhibiting conspicuous, unique anatomical characteristics. Among these, members of Tanystropheidae (Reptilia: Archosauromorpha) displayed cervical vertebral elongation to an extent unparalleled in any other vertebrate. Tanystropheids were exceptionally ecologically diverse and had a wide spatial and temporal distribution. This may have been related to their neck anatomy, yet its evolution and functional properties remain poorly understood. We used geometric morphometrics to capture the intraspecific variation between the vertebrae comprising the cervical column among early archosauromorphs, to trace the evolutionary history of neck elongation in these animals. Our results show that the cervical series of these reptiles can be divided into modules corresponding to those of extant animals. Tanystropheids achieved neck elongation through somite elongation and a shift between cervical and thoracic regions, without presacral vertebrae count increase—contrary to crown archosaurs. This suggests a peculiar developmental constraint that strongly affected the evolution of tanystropheids. The data obtained just at the base of the archosauromorph phylogenetic tree are crucial for further studies on the modularity of vertebral columns of not only Triassic reptile groups but extant and other extinct animals as well.
... One of those taxons is Tanystropheus (Meyer 1852), a genus of archosauromorph reptiles with possibly an aquatic habit and whose fossil record extends from the Late Permian to the Early Triassic (Ezcurra 2016). This taxon possessed the longest necks ever recorded relative to the size of the torso, with neck length approximating half of total body length and containing 13 elongated cervical vertebrae with hollow vertebral bodies (Renesto 2005;Nosotti 2007;Taylor and Wedel 2013). Since the influence of the dead space volume is related to the dimension of the airways, mainly the trachea and extrapulmonary bronchi in non-mammalian amniotes, the long neck in Tanystropheus should have a great influence on the animal's respiratory and metabolic physiology. ...
... The ecology of Tanystropheus is still very poorly understood (Renesto 2005). While the genus has been consistently attributed to marine habitats (Nosotti 2007;Renesto and Saller 2018;Spiekman et al. 2020), its capacity for either terrestrial or aquatic locomotion is still being debated. ...
... While the genus has been consistently attributed to marine habitats (Nosotti 2007;Renesto and Saller 2018;Spiekman et al. 2020), its capacity for either terrestrial or aquatic locomotion is still being debated. The low number of cervical vertebrae, their articulations, and the presence of cervical ribs indicates poor mobility of the neck, mainly restricted to vertical movements (Renesto, 2005). A neck representing about 1/3 of the animal's body mass represents a significant challenge for an elevation above the ground or water, and a significant body mass should be present in the trunk and tail. ...
All known species of the Triassic archosauromorph genus Tanystropheus are known to have had the longest neck in proportion to their torso. This feature is related to a series of ventilatory challenges since an increase in neck length also increases airway length and, therefore, the volume of stagnant air that does not reach the lungs, the dead space volume. Based on this challenge, the objective of the present study was to model the type of respiratory system of Tanystropheus able to meet its metabolic demands during the early Triassic period. The modeling was based on allometric relations for morphological and physiological ventilatory and metabolic variables, and to do so, the mean body mass of Tanystropheus was estimated based on three different methods. In addition, the tracheal airflow was also estimated based on the proportions of Tanystropheus elongated neck, the results of allometric modeling, and fundamental equations of fluid mechanics. The estimation of the body mass indicated that an animal of 3.6 m would possess a body mass of 50.6 ± 21.6 kg. Allometric modeling suggested that the respiratory system best suited to Tanystropheus' oxygen demands, especially during activity, would be a generic reptilian-like respiratory system composed of multicameral lungs. The best respiratory pattern to maintain adequate tracheal flow rates and effective pulmonary ventilation would be one ventilating the relatively narrower trachea at lower frequencies to deal with tracheal dead space volume.
... In the anterior and middle sections of the tail, the transverse processes are often flat and wide in the anterior-posterior direction, approaching each other, sometimes even touching (Fig. 9). Such morphology of transverse processes in modern mammals, namely sirenians, limits the lateral bends of the tail in its anterior and middle sections, which was most likely also true for fossil reptiles with a similar morphology of these processes (Renesto, 2005;Renesto and Saller, 2018). In such reptiles, just as in mammals having a wide and flat tail that acts in the vertical plane when swimming, the length of the transverse processes of the caudal vertebrae does not ...
... On the other hand, among the early archosauromorphs, vertical movements of the tail during swimming were probably used by the marine, sauropterygian-like eosuchian Claudiosaurus (McMenamin, 2019), as well as aquatic prolacertylians, the tanystropheids (Renesto, 2005;Sennikov, 2015Sennikov, , 2019Renesto and Saller, 2018), which had an anteriorly wide and flat tail. The discovery of traces of Gwyneddichnium, attributed to tanystropheids, most likely to Tanytrachelos, with synchronous support on hind limbs touching the bottom, are important evidence supporting the use of the vertical flexibility of the spine when (Renesto and Saller, 2018). ...
... This condition is even more distinct in Tanystropheus spp., in which the neural spine in the mid-cervical vertebrae is reduced to small dorsal extensions of the neural arch near the anterior and posterior ends of the vertebra (Spiekman & Scheyer, 2019;Wild, 1973). It has been suggested that this reduction of the cervical neural spines corresponds to a reduced attachment area for the adductor musculature of the neck, and correspondingly, that dorsiflexion of the neck was limited in these taxa (Tschanz, 1986(Tschanz, , 1988; but see Renesto, 2005). Gracilicollum latens, in contrast, has comparatively taller cervical neural spines with a straight distal margin in lateral view that also possesses a slight transverse expansion (Wang et al., 2023b). ...
Some of the earliest members of the archosaur-lineage (i.e., non-archosauriform archosauromorphs) are characterised by an extremely elongated neck. Recent fossil discoveries from the Guanling Formation (Middle Triassic) of southern China have revealed a dramatic increase in the known ecomorphological diversity of these extremely long-necked archosauromorphs, including the fully marine and viviparous Dinocephalosaurus orientalis. These recent discoveries merit a reinvestigation of enigmatic Triassic diapsid fossils from contemporaneous European deposits housed in historical collections. Here, we provide a redescription of Trachelosaurus fischeri, represented by a single, disarticulated specimen first described in 1918. Due to its unique morphology, which includes short, bifurcating cervical ribs, and a high presacral vertebral count, this taxon has been referred to either as a “protorosaurian” archosauromorph or a sauropterygian. Our revision clearly shows that Trachelosaurus represents the first unambiguous Dinocephalosaurus- like archosauromorph known from outside the Guanling Formation. Our finding has important systematic implications. Trachelosauridae Abel, 1919 represents the senior synonym for the recently identified Dinocephalosauridae Spiekman, Fraser and Scheyer, 2021. Based on our phylogenetic analyses, which employ two extensive datasets, we also corroborate previous findings that tanystropheids and trachelosaurids represent two families within a larger monophyletic group among non-crocopodan archosauromorphs, which is here named Tanysauria (clade nov.). Trachelosauridae is minimally composed of Trachelosaurus fischeri, Dinocephalosaurus orientalis, Pectodens zhenyuensis, and Austronaga minuta, but one of our analyses also found a probably taxonomically broader clade that may also include Gracilicollum latens and Fuyuansaurus acutirostris. Trachelosaurus fischeri considerably expands the known spatial and temporal range of Trachelosauridae to the earliest Anisian and the Central European Basin. Our findings add to the growing evidence for the presence of a diverse group of fully marine reptiles during the Middle Triassic
... Bone density analysis showed the sauropterygian Lariosaurus to be more clearly adapted to a fully aquatic lifestyle than Tanystropheus, which on that basis was inferred to have been amphibious . Fishing from the shoreline (Renesto 2005) has not been generally accepted as a mode of predation in Tanystropheus hydroides (Nosotti 2007;Renesto & Saller 2018;Spiekman et al. 2020aSpiekman et al. , 2020b, and we consider it highly unlikely that it habitually emerged onto land: its long, straight and rigid neck making extended movement on land improbable (Tschanz 1986). If it was difficult for Tanystropheus hydroides to move on land then it would have been impossible for Dinocephalosaurus orientalis. ...
The non-archosauriform archosauromorph Dinocephalosaurus orientalis was first described from the Upper Member of the Guanling Formation (late Anisian, Middle Triassic) of Guizhou Province by Li in 2003 on the basis of a complete articulated skull and the first three cervical vertebrae exposed in dorsal to right lateral view. Since then, additional specimens have been discovered in southwestern China. Here, five newly discovered specimens are described for the first time, and redescriptions of the holotype IVPP V13767 and another referred specimen, IVPP V13898, are provided. Together, these permit the description of the complete skeleton of this remarkable long-necked marine reptile. The postcranial skeleton is as much as 6 metres long, and characterised by its long tail and even longer neck. The appendicular skeleton exhibits a high degree of skeletal paedomorphosis recalling that of many sauropterygians, but the skull and neck are completely inconsistent with sauropterygian affinities. The palate does not extend back over the basisphenoid region and lacks any development of the closed condition typical of sauropterygians. The arrangement of cranial elements, including the presence of narial fossae, is very similar to that seen in another long-necked archosauromorph, Tanystropheus hydroides, which at least in part represents a convergence related to an aquatic piscivorous lifestyle. The long and low cervical vertebrae support exceptionally elongate cervical ribs that extend across multiple intervertebral joints and contribute to a ‘stiffening bundle of ribs’ extending along the entire ventral side of the neck, as in many other non-crocopodan archosauromorphs. The functional significance of the extraordinarily elongate neck is hard to discern but it presumably played a key role in feeding, and it is probably analogous to the elongate necks seen in pelagic, long-necked plesiosaurs. Dinocephalosaurus orientalis was almost certainly a fully marine reptile and even gave birth at sea.
... So far we have recognized more than 500 isolated bones of this taxon in the identified material, more than from any other site reported to this date. The lifestyle and use of extremely elongated neck of Tanystropheus is a hotly debated topic among paleontologists (Beardmore & Furrer, 2018;Jaquier & Scheyer, 2017;Nosotti, 2007;Renesto, 2005;Renesto & Saller, 2018;Rieppel et al., 2010;Spiekman & Scheyer, 2019;Spiekman et al., 2020aSpiekman et al., , 2020bSpiekman et al., , 2021. Remains of this genus are usually present in the coeval sites from the Germanic Basin, but so far have been reported only in relatively low quantities (Hagdorn, 1990;Hagdorn & Reif, 1988;Klein et al., 2022;Schoch, 2015;Schoch & Seegis, 2016;Schoch et al., 2022). ...
The Middle Triassic remains a poorly understood time in the evolution of land vertebrates. Here, we report a new Ladinian-age vertebrate assemblage from Miedary (southern Poland). It consists of more than 20 taxa including fish (four
species of Hybodontiformes, cf. Gyrolepis, Redfieldiiformes, ‘Thelodus’, Saurichthys, Serrolepis, Prohalecites, Ptychoceratodus), amphibians (Mastodonsaurus, Gerrothorax, Plagiosternum, chroniosuchian Bystrowiella), and reptiles (Owenettidae, Blezingeria, Nothosaurus, Tanystropheus, an additional, yet unidentified tanystropheid, the doswelliid Jaxtasuchus, and another archosauromorph, as well as eight archosauriform tooth morphotypes). Preliminary comparisons suggest biogeographic and environmental similarities with roughly contemporaneous localities known from the southwestern part of the Germanic Basin. Among differences in these two areas are the presence of a new armored archosauromorph and a surprising abundance of Tanystropheus remains in the new Polish site. Miedary is currently the richest source of three-dimensionally preserved Tanystropheus material in the world, which will be crucial for a better understanding of the preferred environment and lifestyle of this highly specialized reptile.
... Late Triassic, Canada (Sues & Olsen, 2015) and Chinle Formation, New Mexico (Pritchard et al., 2015). terrestrial, semi-aquatic, entirely aquatic, and even gliding forms (Benton, 2016;Dzik & Sulej, 2016;Ezcurra, 2016;Renesto, 2005). Some tanystropheids are considered terrestrial, including Macrocnemus, Elessaurus gondwanoccidens and Langobardisaurus. ...
... (13 cervical vertebrae in total) and primarily through the addition of cervical vertebrae in Dinocephalosaurus (33 cervical vertebrae in total in IVPP V 20295; Li et al., 2004). Considering their remarkably elongate necks, the evolution of the highly derived anatomy of the cervical vertebrae and ribs in these taxa and closely related forms and its potential functional implications are particularly relevant (for discussions of vertebral column morphology and function in Tanystropheus, see, among others: Renesto, 2005;Renesto & Saller, 2018;Spiekman et al., 2020b;Tschanz, 1986; and for Dinocephalosaurus, see: Demes & Krause, 2005;LaBarbera & Rieppel, 2005;Li et al., 2004;Peters, 2005). ...
A long neck is an evolutionary innovation convergently appearing in multiple tetrapod lineages, including groups of plesiosaurs, non-archosauriform archosauromorphs, turtles, sauropodomorphs, birds, and mammals. Among all tetrapods both extant and extinct, two Triassic archosauromorphs, Tanystropheus and Dinocephalosaurus, have necks that are particularly elongated relative to the lengths of their trunks. However, the evolutionary history of such hyper-elongated necks in these two archosauromorph clades remains unknown, partially because known close relatives such as Macrocnemus and Pectodens possess only moderately elongated necks. Here, we describe a newly discovered early diverging archosauromorph, Gracilicollum latens gen. et sp. nov., based on a specimen comprising a partial neck and an incompletely preserved skull. The long neck is composed of at least 18 cervical vertebrae. The dentition suggests that this new taxon most likely represents an aquatic piscivore, similar to Dinocephalosaurus and Tanystropheus hydroides. Despite possessing a high number of cervical vertebrae, Gracilicollum gen. nov. is recovered as a tanystropheid in an evolutionary grade between Macrocnemus and Tanystropheus rather than as a close relative of Dinocephalosaurus, a result that is primarily attributable to the presence of palatal teeth and the anatomy of the cervical vertebrae in Gracilicollum gen. nov. Considering the information provided by the new specimen, we provide a detailed discussion of the cervical evolution in dinocephalosaurids and tanystropheids, which is shown to be highly complex and mosaic in nature.
In ancient and modern aquatic and semi-aquatic tetrapods, several types of structure of the locomotor apparatus are presented, providing various styles of swimming. In the course of evolutionary adaptation to swimming, an important role was played by the morphological transformations of the tail, which often performs the main propulsion function. Modern reptiles (except turtles) swim mainly with the help of horizontal tail bends, while mammals swim either vertical or horizontal ones. Among extinct reptiles, Sauropterygia probably used vertical tail mobility when swimming. In most archosauromorphs, the tail became high, laterally compressed, and they swam mainly with the help of its horizontal movements. Among early archosaurs, Proterohampsians and Doswelliids are distinguished by their wide and dorsoventrally flat tails, which may indicate an adaptation to swimming using its vertical mobility.
Marine conservation deposits (‘Konservat-Lagerstätten’) are characterized by their mode of fossil preservation, faunal composition and sedimentary facies. Here, we review these characteristics with respect to the famous conservation deposit of the Besano Formation (formerly Grenzbitumenzone; including the Anisian–Ladinian boundary), and the successively younger fossil-bearing units Cava inferiore, Cava superiore, Cassina beds and the Kalkschieferzone of Monte San Giorgio (Switzerland and Italy). We compare these units to a selection of important black shale-type Lagerstätten of the global Phanerozoic plus the Ediacaran in order to detect commonalities in their facies, genesis, and fossil content using principal component and hierarchical cluster analyses. Further, we put the Monte San Giorgio type Fossillagerstätten into the context of other comparable Triassic deposits worldwide based on their fossil content. The results of the principal component and cluster analyses allow a subdivision of the 45 analysed Lagerstätten into four groups, for which we suggest the use of the corresponding pioneering localities: Burgess type for the early Palaeozoic black shales, Monte San Giorgio type for the Triassic black shales, Holzmaden type for the pyrite-rich black shales and Solnhofen type for platy limestones.
A juvenile Macrocnemus bassanii from Besano shows remains of scale covering in the sacral and proximal caudal region. The scales are preserved as fossilized elements and not as impressions. By comparison with another specimen of Macrocnemus, a taphonomic model is proposed to explain the pattern of preservation; suggesting that rapid burial in marine sediment occurred just after death, and that the well developed musculature of the sacral and proximal caudal regions contributed to the process of phosphatization of the scales, allowing their fossilization.
Rynhcosauroides tirolicus (Abel, 1926) is the first ichnite of Triassic tetrapods known from the South-eastern Alps. The recent discovery of new tracks and trackways also permits, for the first time, the documentation of trackway pattern and to calculate the dimensions and possible functional dynamics of the author of this form which appears peculiar to the upper Anisian deposits of the Southern Alps. A tentative palaeontological attribution of Rhynchosauroides tirolicus and other Middle Triassic Rhynchosauroides trackmaker suggest with some confidence, that the morphology of the trackmakers matches the structure of prolacertiform reptiles like Macrocnemus bassanii Nopcsa, 1931 if this latter is reconstructed with a not fully plantigrade manus and pes, but rather with a semi-plantigrade manus and a digitigrade pes.
Boreopricea funerea from the Lower Triassic of northern Russia is a prolacertiform diapsid, superficially similar to Prolacerta from the Lower Triassic of South Africa. The skull is damaged, but relatively complete. The lower temporal bar is absent. Some parts of the skeleton of Boreopricea, in particular some of the vertebrae and the foot, are well preserved, and offer clear evidence of prolacertiform affinities. Nineteen species of prolacertiform have been described. Their affinities are difficult to resolve because available specimens for many of the taxa are incomplete. A series of cladistic analyses shows the existence of a tanystropheid clade (Tanystropheus, Tanvtrachelos), to which are allied Cosesaurus, Malerisaurus, Boreopricea, and Macrocnemus as successive outgroups. A new synapomorphy of prolacertiforms may be the tight association of astragalus, calcaneum, centrale, and distal tarsal 4 in the ankle, with the centrale in contact with the tibia.