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Body outlines of large (> 1 m total body length) extinct and extant vertebrates, primarily or secondarily adapted to the marine environment. A. Plesiosaurus sp., an extinct Jurassic plesiosauromorph plesiosaur. B. Thunnus thynnus, the extant Atlantic bluefin tuna, a teleost " fish ". C. Car charodon carcharias, the extant great white shark. D. Hydrurga leptonyx, the extant leopard seal. E. Physeter macrocephalus, the extant sperm whale. F. Tursiops truncatus, the extant common bottlenose dolphin. G. Platecarpus sp., an extinct Cretaceous mosasaur. H. Ichthyosaurus sp. an extinct Jurassic ichthyosaur. Note how the plesiosaur is the only large marine vertebrate with a long neck. Images not to scale.
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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...
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 . ...
