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Cervical vertebrae and cervical centra of plesiosaurs. A. Generalized plesiosaur cervical vertebra showing features mentioned in the text in oblique antero-left lateral view (note: not all features are present in all species). B. Posterior cervical vertebra of Muraenosaurus beloclis illustrating the form as preserved in anterior view (note the wider than high form of the centrum, typical of all plesiosaurs). Illustrative vertical cross-sections through the articular surfaces (to the left) of Muraenosaurus (C) and Cryptoclidus (D), showing variation in cross-sectional shape between genera, which may have affected the range of movement available at contiguous cervical joints (data from Brown 1981b). E. Illustrative articular face of a Cretaceous elasmosaur cervical vertebra, showing the laterally expanded butterfly-or dumbbell-shape. F–I. Views of a generalized plesiosaur cervical centrum (anterior face to the left), showing features mentioned in the text, in anterior (F), dorsal (G), left lateral (H), and ventral (I) views. Images from: B, Andrews (1910: pl. 7: 4); A, C–I, LFN drawings.
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The evolution and function of the long neck in plesiosaurs, and how the problems associated with stiffness or flexibility were overcome during feeding, or rapid swimming during predator avoidance, are explored, and a new interpretation for the function of the plesiosaur neck is presented. Based on the anatomy of the articular faces of contiguous ce...
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... centra: The anterior face of the atlas centrum forms the deep cup-shaped articulating surface to receive the basioccipital condyle of the skull (Fig. 6B). In Muraenosaurus the posterior articular face of the axis and both articular faces of the postaxial cervical centra are relatively platycoelous, but develop a shallow V-shape in cross-section ( Fig. 7C) with sharply defined borders with increasing age (Andrews 1910;Brown 1981b). In Cryptoclidus and Tricleidus, the vertebrae are amphicoelous (Evans 1993), especially in old individuals, with more rounded margins (Fig. 7D), producing a double sigmoidal curve in cross-section (Andrews 1910;Smellie 1915Smellie , 1916Brown 1981b). The more ...
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... articular faces of the postaxial cervical centra are relatively platycoelous, but develop a shallow V-shape in cross-section ( Fig. 7C) with sharply defined borders with increasing age (Andrews 1910;Brown 1981b). In Cryptoclidus and Tricleidus, the vertebrae are amphicoelous (Evans 1993), especially in old individuals, with more rounded margins (Fig. 7D), producing a double sigmoidal curve in cross-section (Andrews 1910;Smellie 1915Smellie , 1916Brown 1981b). The more rounded margins of the cervical centra in Cryptoclidus may indicate that relatively more movement was possible between the vertebrae than in Muraenosaurus (Brown ...
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... the length of the neck (Andrews 1910;Smellie 1916;Brown 1981b). This pattern of wider- than-high vertebral proportions is seen in all plesiosaurs (Watson 1924), irrespective of how the measurements are taken (e.g., Welles 1943Welles , 1952Brown 1981b). However, the broadening of cervical centra is most clearly expressed in Cretaceous elasmosaurs (Fig. 7E), where the vertebrae are commonly butterfly-or dumb-bell shaped (e.g., O'Keefe 2001a; O' Keefe and Hiller ...
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... neural arches: The dorsomedial surface of each cervical centrum exhibits a concave excavation for the neural canal between the facets for the neural arch (Andrews 1910). Viewed dorsally, the neural canal is hour- glass-shaped, constricted medially, and widest posteriorly (Fig. 7G). Bounding the neural canal on each side are large diamond-shaped facets for reception of the pedicles of the neural arch. The neural arch extends almost the full length of the centrum (Andrews 1910;Brown 1981b) and thereby forms the lateral and dorsal margins of the neural canal. In Muraenosaurus, the neural canal and neural arch ...
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... atlas bears a low, divided, strongly posteriorly-slop- ing neural arch with well-developed posterior zygapophyses; the axis neural arch is larger, with both anterior and posterior zygapophyses. In the postaxial cervical vertebrae (Fig. 7A), the neural arch narrows dorsally before widening to bear the dorsomedially directed anterior, and the ventrolaterally fac- ing posterior, zygapophyses which are strong and well-devel- oped throughout the cervical series in all plesiosaurs (Brown 1981b). In Oxford Clay genera, the zygapophyses are oval and overhang the articular ...
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... centra surface ornamentation: On the postax- ial cervical vertebrae, the anterior and posterior margins of the centra, particularly the lateral and ventral surfaces, ex- hibit ornamentation in bands adjacent to the articular faces (Fig. 7A, G). This ornamentation becomes more pronounced with increased age (Brown 1981b): for instance, in "juve- nile" individuals of Muraenosaurus the ornamentation is relatively regular, closely-spaced longitudinal ridges ("pli- cations" of Andrews 1910), which in "adults" ossifies to be- come more strongly developed irregular rugosities, ...
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... the ridge only extends from the atlas onto the anterior of the axis; in Tricleidus the hypophysial ridge is less well-developed anteriorly, but extends to the rear of the axis (Andrews 1910). In plesio- saurs generally, the ventral surfaces of the postaxial centra are gently concave anteroposteriorly and normally exhibit paired nutritive foramina (Fig. 7G), although these foramina may be variably expressed: duplicated, coalesced or absent. The nutritive foramina lie close together anteriorly, but are gradually separated by a low mid-ventral ridge which be- comes less prominent posteriorly where the foramina are more widely spaced (Andrews 1910;Smellie 1916;Brown 1981b). The nutritive ...
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... Muraenosaurus, the cervical centra exhibit a lateral longitudinal ridge (Fig. 7A, G) midway between the base of the neural arch and the top of the cervical rib (Seeley 1874;Andrews 1910). The ridge is generally absent in juveniles where the cervical vertebrae are less well ossified, but is often especially prominent in the anterior half of the neck of older individuals; a similar lateral crest is present in various ...
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... neural spines exhibit ornamentation of the bone surface. In Cryptoclidus the base of the axis neural spine is developed into a strong ridge, not seen in Muraenosaurus. In the anterior cervical vertebrae of Cryptoclidus, the zyga- pophyses are connected by a ridge on the lateral surface of the neural spine (Fig. 7A), which disappears in the posterior of the neck (Andrews 1910;Brown 1981b), allowing the sides of the pedicles to pass uninterrupted into the neural spines. In addition, some specimens of Cryptoclidus exhibit an oblique, roughened ridge (Fig. 7A) sloping anteroven- trally approximately halfway between the line of the zyga- pophyses and ...
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... Cryptoclidus, the zyga- pophyses are connected by a ridge on the lateral surface of the neural spine (Fig. 7A), which disappears in the posterior of the neck (Andrews 1910;Brown 1981b), allowing the sides of the pedicles to pass uninterrupted into the neural spines. In addition, some specimens of Cryptoclidus exhibit an oblique, roughened ridge (Fig. 7A) sloping anteroven- trally approximately halfway between the line of the zyga- pophyses and the tip of the neural spine (Smellie 1916). In Muraenosaurus, Tricleidus and Cryptoclidus the summits of the neural spines are abruptly truncated by a roughened, subtly V-shaped, indented dorsal surface (Seeley 1874;Andrews 1910;Brown ...
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... the neck musculature. The triradiate shape of the postaxial cervical vertebral seg- ments (Fig. 10C), and the presence of roughened surfaces on the centra, neural spines and cervical ribs, all indicate the presence of strong cervical musculature and ligamentous ties. The anterior and posterior areas of ornamentation on the cervical vertebrae (Fig. 7A, G) have been interpreted as the attachment points for ligaments tying adjacent verte- brae together strongly (Brown 1981b). Bony ridges indicate the presence of strong neck musculature (Hawkins 1840), well-supplied with blood vessels (some passing through the subcentral foramina) and nerves (passing between the verte- Fig. 10. The range ...
Citations
... All cervical vertebrae of plesiosaurs show a pair of large foramina on the ventral surface of the vertebral centrum, called subcentral foramina or subcentralia (Romer, 1956), and are autapomorphy of the clade (Storrs, 1991;o'Keefe, 2001;Benson & Druckenmiller, 2014;Noè et al., 2017;Wintrich et al., 2017b). Storrs (1991) In the middle section of the pectoral vertebra, two ventral foramina and two dorsal foramina are discernible (Fig. 2). ...
Abstract. Elasmosaurids were the most diverse forms of plesiosaurs during the Late Cretaceous and achieved a cosmopolitan distribution. Thus, its fossils have been recorded on all continents, including Antarctica. Knowledge of paleobiological and evolutionary aspects of plesiosaurs has advanced considerably in recent years, including microstructural and paleohistological analyses of bone tissue. However, comparative analyses are still relatively scarce. To analyze how the degree of remodeling varies in the vertebral column of Vegasaurus molyi (MLP 93-I-5-1), from the Upper Cretaceous of Antarctica, histological sections of four vertebrae representing different sections of the column were made. The sections present a high degree of remodeling and an external fundamental system, indicating that the individual has reached skeletal maturity. The caudal vertebra shows the least degree of remodeling and retains the greatest number of lines of arrested growth. The results indicate that the degree of bone remodeling increases from the caudal region to the cervical region. When considering the middle sections of the vertebral elements, there is an increase in the compaction index from the cervical region to the caudal region. These differences in the bone microstructure are perceptible and serve as a criterion for determining which element of the vertebral column and in which part of its thin sections should be created. This will yield more information at the paleohistological level, allowing paleobiological inferences such as ontogenetic stage, differential growth of various parts of the skeleton, and blood supply, among other factors.
... This is not to say that euungulate-style nuchal ligaments sensu stricto, or nuchal-ligament-like interspinal elastic ligaments (as in Rhea), in sauropod necks are impossible; merely that appropriate testing for correlates of such ligaments has not yet been conducted to support such hypotheses. Assumptions that 'large', 'heavy', and 'long' heads and/or necks correlate with nuchal ligaments have been pervasive over time and across taxa (e.g., Hildebrand 1974;Alexander 1989;Bray and Burbidge 1998;Gellman and Bertram 2002b;Stevens and Parrish 2005;Mitchell et al. 2013;Haussler 2016;Arnold et al. 2017;Noè et al. 2017;Titov et al. 2021;Domning 2022). I emphasize, however, that while these assumptions remain largely untested, they are not necessarily incorrect. ...
Nuchal ligaments are relatively well understood and have venerable histories of recognition in extant euungulates, canids, elephants, and humans, but whether any anatomical structures in other taxa, both extant and extinct, qualify as nuchal ligaments is unclear because the term ‘nuchal ligament’ lacks a clear, narrow, consistently applied definition. Possible definitions of the term could be etymological, taxonomic, compositional, or morphological/topological, or a combination thereof. Currently, a de facto morphological/topological definition of ‘nuchal ligament’ sensu stricto seems most common: a nuchal ligament is an epaxial, cervical ligament with a funiculus that is elevated above the cervical spinous processes and connected to them only via laminae. However, many references to ‘nuchal ligaments’ in both extant and extinct taxa instead seem to employ a broader, etymological definition that encompasses numerous different compositions, morphologies and topologies. Several, largely untested assumptions have been made about functional and osteological correlates of a nuchal ligament, such as possessing a ‘large’ or ‘heavy’ head and/or a ‘long’ neck, possessing specific features on the occipital region of the skull, and possessing specific morphologies or dimensions of the cervical and cranial thoracic spinous processes. These assumptions have led to corollary assumptions that many extinct tetrapods—particularly those phylogenetically far removed from taxa known to possess them—had nuchal ligaments, but until these presumed correlates are tested and demonstrated in extant taxa, such assumptions remain purely speculative, and alternative cranio-cervical support mechanisms also must be considered. Depending on the definition applied, attributions of nuchal ligaments to extinct taxa, and even to some extant taxa (including humans), may be references to other sorts of morphologically and topologically distinct epaxial structures such as supraspinous ligaments and fibrous septa/raphes that occupy similar anatomical positions as nuchal ligaments sensu stricto. ‘Nuchal ligament’ requires a narrow definition to understand what, if any, features correlate with the presence of the ligament, as well as what taxa have convergently evolved the structure.
... Specifically, in the Pierce II Guild, plesiosauroids fall in an area of the morphospace defined by the shortest mandibular symphysis length, highest TI and highest MA values as well as the smallest jaw length in our dataset (figures 2, 5 and 6). This suggests that plesiosauroids adopted a unique foraging strategy [15,33,67], different from that of other taxa in the Pierce Guild (i.e. the 'trap guild' proposed by Chatterjee and Small [68]. This separation supports the original subdivision in Pierce I and Pierce II by Massare [9], a split that could not be confirmed by the dentition-only study by Foffa et al. [5]. ...
... This combination of features indicates that plesiosauroids probably adopted a different feeding strategy (i.e. filter/sieve/straining feeding, raking sediments [15,33,67] or 'Trap Guild' [68] than other members of the Pierce Guild. In Pierce II sub-Guild, small-bodied pliosaurids, longirostrine teleosauroids and metriorhynchines are characterized by relatively weak force transmission to the bite point, have gracile jaws, with long protruding mandibular symphyses and, crucially, fast-opening jaw mechanisms (figures 5-8; electronic supplementary material, appendix S5). ...
Mesozoic marine ecosystems were dominated by diverse lineages of aquatic tetrapods. For over 50 Ma in the Jurassic until the Early Cretaceous, plesiosaurians, ichthyosaurians and thalattosuchian crocodylomorphs coexisted at the top levels of trophic food webs. We created a functional dataset of continuous craniomandibular and dental characters known from neontological studies to be functionally significant in modern aquatic tetrapods. We analysed this dataset with multivariate ordination and inferential statistics to assess functional similarities and differences in the marine reptile faunas of two well-sampled Jurassic ecosystems deposited in the same seaway: the Oxford Clay Formation (OCF, Callovian–early Oxfordian, Middle–Late Jurassic) and the Kimmeridge Clay Formation (KCF, Kimmeridgian–Tithonian, Late Jurassic) of the UK. Lower jaw-based macroevolutionary trends are similar to those of tooth-based diversity studies. Closely related species cluster together, with minimal overlaps in the morphospace. Marine reptile lineages were characterized by the distinctive combinations of features, but we reveal multiple instances of morphofunctional convergence among different groups. We quantitatively corroborate previous observations that the ecosystems in the OCF and KCF were markedly distinct in faunal composition and structure. Morphofunctional differentiation may have enabled specialization and was an important factor facilitating the coexistence of diverse marine reptile assemblages in deep time.
... Dating back to the 19th and 20th centuries, plesiosaurs were often reconstructed as animals patrolling around the water surface with swan-like or snake-like necks (Fig. 2AB). However, recent studies have demonstrated that such a bending of the neck is impossible for plesiosaurs [64,86]. This posture never appears in articulated fossils either. ...
Body size is the key to understanding many biological properties. Sizes of extinct animals are usually estimated from body reconstructions since their masses can not be weighed directly. Plesiosaurs were Mesozoic marine reptiles that were diverse in both body plan and size. Attempts to estimate body masses of plesiosaurs were rare in the past two centuries, possibly due to lack of knowledge about their postcranial anatomy and body shapes in life. The burst of plesiosaur studies in the past two decades has greatly expanded our cognition of their physiology, taxonomy, potential behavior and even soft body outlines. Here I present a comprehensive review of relevant knowledge, and propose a uniform set of methodology for rigorous body reconstruction of plesiosaurs. Twenty-two plesiosaur models were constructed under these criteria, and they were subsequently used as samples to find proxies for body mass. It is revealed that multiple skeletal elements are good indicators of plesiosaur size. This study offers scaling equations for size estimation, enabling quick acquisition of body mass information from fragmented fossils. A summary of body size evolution of different plesiosaur clades is also provided.
... These in turn provided food for durophagous fishes and marine reptiles and macropredatory reptiles that fed on fishes and other reptiles [47]. Long necks likely evolved as an adaptation to snapping rapidly at the faster swimming fishes of the new ecosystems or dipping for benthic prey in murky seabed sediments [48]. ...
... We suggest here that variations in the neck length of eosauropterygians may reflect different feeding strategies as well: a typical short-necked pliosauromorph is regarded as the apex predator in Mesozoic marine ecosystems, while some of the long-necked plesiosaurs were more likely to be mesophagous, with their long neck enabling them to pursue smaller prey such as fast-moving fishes or benthic animals, like bivalves on the seabed [48,50,58]. In these cases, the long, flexible neck with many cervical vertebrae, would enable the hunter to flip its head faster in pursuit of fishes than by moving the whole body, or to search for food over a wide area on the murky seabed without constantly moving the body. ...
Neck elongation has appeared independently in several tetrapod groups, including giraffes and sauropod dinosaurs on land, birds and pterosaurs in the air, and sauropterygians (plesiosaurs and relatives) in the oceans. Long necks arose in Early Triassic sauropterygians, but the nature and rate of that elongation has not been documented. Here, we report a new species of pachypleurosaurid sauropterygian, Chusaurus xiangensis gen. et sp. nov., based on
two new specimens from the Early Triassic Nanzhang-Yuan’an Fauna in the South China Block. The new species shows key features of its Middle Triassic relatives, but has a relatively short neck, measuring 0.48 of the trunk length, compared to > 0.8 from the Middle Triassic onwards. Comparative phylogenetic analysis shows that neck elongation occurred rapidly in all Triassic eosauropterygian lineages, probably driven by feeding pressure in a time of rapid re-establishment of new kinds of marine ecosystems.
... An elongated neck has appeared several times throughout the evolution of tetrapods, both in extinct and extant groups, conveying a series of mechanical challenges and several anatomical novelties (Taylor and Wedel 2013). These challenges are often related to the breathing capacities of long-necked animals, since an increase in neck length also increases airway length and, therefore, the volume of stagnant air that does not reach the lungs, termed the dead space volume (Otis 1964;Noè et al. 2017). Gas exchange between air and blood occurs only within the pulmonary epithelium and, to get there, the inspired air passes through the airways. ...
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.
... Therefore, here we question this association between FR and drag also for plesiosaurs. Long necks have also been argued to add extra viscous drag due to their large surface area as well to increase pressure drag 7,25,30 . A recent CFD-based study of plesiosaurs concluded that drag was not affected by neck length during forward motion 20 . ...
... The limits of the trunk (which extends along the torso and includes the edges of the pectoral and pelvic girdles) are shown in red in the rendered models. that long necks produce only a small increase in skin friction, although not as great as previously speculated 25,30 , and this is nullified by reduced pressure drag. ...
Various Mesozoic marine reptile lineages evolved streamlined bodies and efficient lift-based swimming, as seen in modern aquatic mammals. Ichthyosaurs had low-drag bodies, akin to modern dolphins, but plesiosaurs were strikingly different, with long hydrofoil-like limbs and greatly variable neck and trunk proportions. Using computational fluid dynamics, we explore the effect of this extreme morphological variation. We find that, independently of their body fineness ratio, plesiosaurs produced more drag than ichthyosaurs and modern cetaceans of equal mass due to their large limbs, but these differences were not significant when body size was accounted for. Additionally, necks longer than twice the trunk length can substantially increase the cost of forward swimming, but this effect was cancelled out by the evolution of big trunks. Moreover, fast rates in the evolution of neck proportions in the long-necked elasmosaurs suggest that large trunks might have released the hydrodynamic constraints on necks thus allowing their extreme enlargement.
... The lineage Xenopsaria Benson and Druckenmiller, 2014 [1] extended into the Cretaceous, and includes the two clades of plesiosauroids, Elasmosauridae Cope, 1869 [5] and Leptocleidia Ketchum and Benson, 2010 [6]. Elasmosauridae is notable for its extreme neck elongation, the function of which is not entirely clear [7][8][9]. The earliest unambiguous representatives of this clade are from the Hauterivian of Europe, and by the Aptian-Albian Elasmosauridae had achieved a global distribution [3,[10][11][12][13][14][15][16][17][18][19][20][21]. ...
We report a new specimen of the plesiosaur Cardiocorax mukulu that includes the most complete plesiosaur skull from sub-Saharan Africa. The well-preserved three-dimensional nature of the skull offers rare insight into the cranial anatomy of elasmosaurid plesiosaurians. The new specimen of Cardiocorax mukulu was recovered from Bentiaba, Namibe Province in Angola, approximately three meters above the holotype. The new specimen also includes an atlas-axis complex, seventeen postaxial cervical vertebrae, partial ribs, a femur, and limb elements. It is identified as Cardiocorax mukulu based on an apomorphy shared with the holotype where the cervical neural spine is approximately as long anteroposteriorly as the centrum and exhibits a sinusoidal anterior margin. The new specimen is nearly identical to the holotype and previously referred material in all other aspects. Cardiocorax mukulu is returned in an early-branching or intermediate position in Elasmosauridae in four out of the six of our phylogenetic analyses. Cardiocorax mukulu lacks the elongated cervical vertebrae that is characteristic of the extremely long-necked elasmosaurines, and the broad skull with and a high number of maxillary teeth (28–40) which is characteristic of Aristonectinae. Currently, the most parsimonious explanation concerning elasmosaurid evolutionary relationships, is that Cardiocorax mukulu represents an older lineage of elasmosaurids in the Maastrichtian.
... A sharp lateral, anteroposteriorly oriented ridge [a feature frequently evolved convergently among long-necked plesiosaurians (e.g. Noè, et al., 2017;Fischer et al., 2018)] is present immediately dorsal to the rib facet in anterior and middle cervical centra (Fig. 3A, G, K, N). Posterior cervicals lack this feature (Fig. 3P). ...
Plesiosaurian marine reptiles evolved a wide range of body shapes during the Jurassic and Cretaceous, including long-necked forms. Many Late Cretaceous members of the clade Elasmosauridae epitomized this part of the plesiosaurian morphological spectrum by evolving extremely long necks through somitogenesis (resulting in an increase in the number of cervical centra) and differential growth (resulting in the elongation of cervical centra). However, the early evolution of elasmosaurids remains poorly understood because of a generally poor Lower Cretaceous fossil record. We describe a new elasmosaurid, Jucha squalea gen. et sp. nov., from the upper Hauterivian (Lower Cretaceous) of Ulyanovsk (European Russia), in addition to other elasmosaurid remains from the same area. Jucha squalea is one of the oldest and basalmost elasmosaurids known and lacks a series of features that otherwise characterize the group, such as the heart-shaped intercoracoid fenestra and the median pectoral bar. However, Jucha squalea marks an early attempt at cervical elongation through differential growth. The data we gathered on the shape of cervical centra among elasmosaurids suggest multiple episodes of elongation and shortening. However, the precise patterns are obscured by an unstable phylogenetic signal.
... Vakil et al., 2020) were plotted against VLIs for all specimens to compare any trends along the length of the vertebral column. Vertebrae were initially assigned to body region based on their morphology, with cervicals bearing rib facets wholly on the centrum, pectorals and sacrals partly on the centrum and neural arch, dorsals wholly on the neural arch, and caudals either on the neural arch or side of the centrum in addition to the presence of chevron facets on their ventral surfaces (e.g., Taylor et al., 1993;Druckenmiller, 2002;Noè et al., 2017). Distinction between anterior and posterior cervicals of elasmosaurids was based on the narrower or wider spacing of the foramina subcentralia in anterior and posterior cervicals, respectively (Bardet et al., 1999;, and with respect to the changing position of rib facets towards the neural arch facets from anterior to posterior cervicals . ...
