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Elasmosaurus

Elasmosaurus is a genus of large, extinct marine reptile belonging to the family Elasmosauridae within the order Plesiosauria, renowned for possessing the longest neck relative to body size among all known vertebrates.^[1] The type and only recognized species, Elasmosaurus platyurus, measured approximately 13 meters (42 feet) in total length, with a neck extending about 7 meters (23 feet) and comprising 72 cervical vertebrae, a small head, and four paddle-like limbs adapted for swimming.^[1] It inhabited the shallow Western Interior Seaway during the Late Cretaceous period, specifically the lower Campanian stage around 83 to 80 million years ago, where it preyed on fish and other marine organisms alongside contemporaries like mosasaurs.^[1]^[2] The holotype specimen of Elasmosaurus platyurus was discovered in the Sharon Springs Formation of western Kansas and first described by American paleontologist Edward Drinker Cope in 1868, a reconstruction in his 1868 description with the skull erroneously placed at the tail end due to incomplete preparation.^[1]^[3] This error was promptly highlighted by Cope's rival, Othniel Charles Marsh, intensifying their infamous "Bone Wars" competition and underscoring the challenges of early vertebrate paleontology.^[3] Cope's description established Elasmosaurus as the eponymous genus of the elasmosaurids, a clade characterized by hyper-elongated necks that likely aided in foraging within the water column.^[1] Subsequent studies, including a 2013 revision, confirmed the exceptional cervical count by rediscovering a missing vertebral element, solidifying Elasmosaurus platyurus as one of the most extreme examples of neck elongation in plesiosaur evolution, comparable only to the closely related Albertonectes vanderveldei with 75 cervicals.^[1] Like other elasmosaurs, it was a fully aquatic reptile that gave live birth and went extinct during the Cretaceous-Paleogene mass extinction event approximately 66 million years ago.^[2] Fossils of Elasmosaurus remain rare, with the holotype housed at the Academy of Natural Sciences of Drexel University providing the primary basis for understanding this iconic Late Cretaceous predator.^[1]

Discovery and research history

Initial discovery and naming

In 1867, the holotype specimen of Elasmosaurus platyurus was discovered by U.S. Army surgeon Theophilus H. Turner near Fort Wallace in western Kansas, within the Sharon Springs Member of the Pierre Shale Formation.^[4] Turner, stationed at the fort during the construction of the Kansas Pacific Railway, initially found vertebral fragments in a ravine approximately 14 miles north of the post in the spring of that year and collected around 900 pounds of bones and enclosing matrix by late December.^[4]^[5] The material, shipped to Philadelphia by mid-March 1868, consisted of a partial skeleton including the skull, portions of the jaws, numerous vertebrae, ribs, and elements of the pectoral and pelvic girdles, housed today as ANSP 10081 at the Academy of Natural Sciences of Philadelphia.^[4]^[6] The specimen was formally named Elasmosaurus platyurus by paleontologist Edward Drinker Cope, who presented his description on March 24, 1868, during a meeting of the Academy of Natural Sciences of Philadelphia.^[4] In his initial publication, Cope highlighted the extraordinary length of the neck, noting over 70 cervical vertebrae that contributed to a total vertebral count exceeding 100, marking it as one of the most distinctive features of this elasmosaurid plesiosaur.^[4]^[7] The full description appeared in the Proceedings of the Academy of Natural Sciences of Philadelphia later that year, with a more detailed account in the Transactions of the American Philosophical Society in 1869.^[4] Cope derived the generic name Elasmosaurus from the Greek words elasmos (thin plate), alluding to the thin, platelike morphology of the vertebrae, and saurus (lizard).^[4] The specific epithet platyurus combines platys (broad or flat) and oura (tail), referring to the broadened appearance of the tail region formed by the expanded neural and haemal spines.^[4] This naming not only established Elasmosaurus as the type genus of the Elasmosauridae family but also contributed to the escalating rivalry between Cope and Othniel Charles Marsh, known as the Bone Wars.^[4]^[6]

Reconstruction controversies and the Bone Wars

In 1868, Edward Drinker Cope published a description of Elasmosaurus platyurus based on a nearly complete skeleton from the Upper Cretaceous of Kansas, but in his reconstruction, he erroneously positioned the skull at the end of the short tail, mistaking the brief series of larger vertebrae for the neck and the extensive chain of over 70 small vertebrae for the tail.^[8] This error stemmed from the incomplete nature of the specimen, which lacked a skull, and Cope's hurried analysis amid growing competition in paleontology.^[9] The reconstruction depicted an unusual plesiosaur with an exceptionally long tail for propulsion, a configuration that deviated from known anatomy of related marine reptiles.030[0545:TBWMCA]2.0.CO;2) The mistake came to light in 1869 when Othniel Charles Marsh, Cope's rival, visited the Academy of Natural Sciences in Philadelphia and immediately recognized the reversal upon viewing the mounted specimen; Marsh privately informed Cope of the error, but Cope attempted to suppress the publication by purchasing available copies of the journal.^[10] Public correction followed in 1870 from anatomist Joseph Leidy, who examined the vertebrae and compared them to those of other plesiosaurs, confirming the long series as the neck and the short one as the tail based on proportional and structural similarities.^[8] Leidy's analysis emphasized the anatomical improbability of Cope's configuration, noting that the supposed "tail" vertebrae lacked the chevron facets typical of caudal elements in reptiles. This incident profoundly humiliated Cope and ignited the personal animosity that defined the Bone Wars, a decades-long rivalry between Cope and Marsh spanning the 1860s to 1890s, marked by mutual accusations of incompetence and sabotage in fossil collecting.^[11] Marsh capitalized on the controversy by publicly mocking Cope's oversight to assert dominance in the field while both men raced to describe new finds from the American West.^[10] The feud exemplified the era's rushed scientific descriptions, often prioritizing priority over accuracy, and spurred an intense wave of competitive fossil hunting across Kansas and Wyoming, yielding thousands of specimens but also numerous taxonomic errors.030[0545:TBWMCA]2.0.CO;2) Ultimately, the Bone Wars advanced American paleontology by accelerating discoveries of Late Cretaceous marine reptiles, though at the cost of ethical lapses and fragmented collections.^[11]

Modern redescriptions and additional specimens

In 2005, paleontologist Sven Sachs provided a detailed redescription of the holotype specimen of Elasmosaurus platyurus (ANSP 10081), an incomplete skeleton collected from the lower Campanian Pierre Shale of western Kansas. This study confirmed the presence of a fragmentary skull (including premaxillae, maxillae, occipital condyle fragments, and dentaries), 71 cervical vertebrae (including the atlas-axis complex), three pectoral vertebrae, six dorsal vertebrae, four sacral vertebrae, and 18 caudal vertebrae, noting that the original pectoral and pelvic girdles had been lost. Sachs revised earlier counts by confirming six premaxillary teeth per side rather than eight.^[12] A significant update came in 2013 when Sachs, along with Johan Lindgren and Benoit Godefroit, rediscovered a previously "lost" cervical vertebra centrum from the holotype, stored separately within the ANSP collections. This fragment, matching the morphology of adjacent neck vertebrae, increased the confirmed cervical count to 72, establishing E. platyurus as possessing one of the longest necks among known vertebrates. The study noted that original excavation records suggested up to three additional cervicals might have been present in the complete individual, potentially raising the total to 75 or 76, though only 72 are now verified, and supported an estimated total body length of approximately 13 meters.^[1] Additional specimens referred to Elasmosaurus have been identified from the Pierre Shale of Kansas, though most remain fragmentary. For instance, a partial skeleton (FHSM VP-398) consisting of seven vertebrae collected near the holotype locality in 1954 has been tentatively assigned to E. platyurus based on matching size and morphology, potentially representing missing elements from the original excavation. Other referred material includes isolated vertebrae and limb fragments from the same formation, but these are limited to incomplete remains without articulated sections.^[4] Debates persist regarding the completeness of known Elasmosaurus specimens, primarily due to extensive erosion at discovery sites and damage sustained during 19th-century excavation and transport. The holotype, for example, shows compression and breakage in many neural processes, complicating precise counts and reconstructions, while no major new, well-preserved skeletons have been reported as of 2025. These challenges underscore the reliance on the holotype for taxonomic understanding, with fragmentary referrals providing only supplementary evidence.^[4]^[13]

Anatomy

Skull and jaws

The skull of Elasmosaurus platyurus was small and triangular in shape, measuring approximately 40–45 cm in length, with a long, rounded snout that comprised over half of the total cranial length.^[14]^[12] The premaxillae were well co-ossified, featuring a low dorsal midline keel and a broad triangular vomeronasal fenestrum medially behind the tooth row.^[12] The dentition was heterodont and adapted for grasping prey, consisting of six teeth per premaxilla, up to 14 per maxilla, and approximately 19 per dentary.^[12]^[15] The teeth were triangular to conical and fang-like, with the anterior ones (particularly the second and third premaxillary) being the largest; crowns were slender with oval to circular cross-sections, fine longitudinal striations on the enamel surface, and cylindrical roots showing resorption pits for replacement.^[12]^[15] The jaws formed an elongate, narrow structure, with the mandible featuring a well-ossified but relatively short symphysis extending posteriorly to the level of the fourth dentary tooth, allowing some flexibility.^[12] There is no evidence of specialized adaptations for crushing or slicing, consistent with a piercing and holding function.^[15] Sensory features included large orbits positioned relatively anteriorly along the maxillopremaxillary suture, indicating well-developed vision suited to underwater hunting.^[14] A lateral line system for detecting water movements was likely present, though inferred primarily from postcranial scalation rather than cranial elements.^[15]

Vertebral column and neck

The vertebral column of Elasmosaurus platyurus is composed of approximately 114 vertebrae in total, distributed as 72 cervical vertebrae in the neck, around 26 dorsal vertebrae in the trunk (including pectoral elements), 2–4 sacral vertebrae, and 18 caudal vertebrae in the tail, based on the holotype specimen and associated fragments.^[1]^[16] The cervical series dominates the axial skeleton, comprising over 60% of the animal's estimated total body length of 13 meters.^[1] The 72 cervical vertebrae (including the atlas-axis complex) are notably elongate, each centrum measuring 10–15 cm in length on average, with mid-series elements longer than they are high or wide, resulting in a neck length of about 7.1 meters.^[1]^[17] These vertebrae feature low neural spines, thin laminae forming prominent lateral longitudinal ridges, and amphicoelous articular surfaces, adaptations that contributed to the exceptional elongation of the neck.^[16] The trunk vertebrae, including robust dorsal elements, provide structural support for the body, with rib facets positioned above the centrum level and higher neural spines than in the cervicals.^[16] The tail is relatively short, terminating in a pointed tip formed by 18 caudal vertebrae that decrease in size posteriorly, accompanied by chevron bones (haemal spines) along the ventral margin for additional support.^[16]

Limbs and body structure

Elasmosaurus possessed four paddle-like limbs adapted for aquatic locomotion, with the forelimbs significantly larger than the hindlimbs. The forelimbs exhibited hyperphalangy, characterized by an increased number of phalanges in the digits—typically ranging from 10 to over 20 per digit in elasmosaurids—allowing for elongated, flattened flippers that spanned approximately 1.5 meters each. These structures featured robust proximal elements, including a flattened humerus, radius, and ulna, transitioning to numerous hyperphalangic phalanges that formed a broad, wing-like surface for propulsion. In contrast, the smaller hindlimbs, measuring around 1 meter in span, served primarily for steering, with similar but less pronounced hyperphalangy.^[15]^[18] The pectoral and pelvic girdles were broad and robust to support flipper articulation. The pectoral girdle included large, triangular scapulae and coracoids with a prominent intercoracoid embayment forming a heart-shaped opening, which accommodated the heart and facilitated ventral positioning for efficient swimming. The pelvic girdle featured expanded ilia and ischia, providing stable attachment points for the hind flippers, though less massive than the pectoral elements. These girdles anchored the limbs to the axial skeleton, enhancing the overall hydrodynamic profile.^[15] The body of Elasmosaurus was a streamlined, compact torso approximately 2 meters long, contributing to its total estimated length of 10–14 meters and a body mass of 2–3 tons. This barrel-shaped form resulted from expanded gastralia and ribs, minimizing drag in marine environments. The skin was likely covered in small, imbricated scales rather than heavy dermal armor, promoting flexibility and reducing weight. The tail was short, terminating in a pointed tip, potentially supporting a small tail fin for fine maneuvering; no dorsal fin was present, with the flippers functioning as primary hydrofoils.^[18]^[19]

Classification

Phylogenetic relationships

Elasmosaurus is classified within the clade Sauropterygia, specifically as a member of Plesiosauria and the family Elasmosauridae, where it occupies a position as a derived elasmosaurid characterized by extreme neck elongation. A phylogenetic analysis by Otero in 2016 positioned Elasmosaurus within the subclade Elasmosaurinae, as the sister taxon to Albertonectes vanderveldei, another Late Cretaceous elasmosaurid from North America.^[20] This analysis utilized a matrix of morphological characters to resolve relationships among plesiosaurs, recovering Elasmosauridae as monophyletic with Elasmosaurus nested among taxa exhibiting the highest cervical vertebral counts. Subsequent work by Serratos, Druckenmiller, and Benson in 2017, building on the dataset from Benson and Druckenmiller (2014), treated Elasmosaurus as a wildcard taxon with variable relationships within Elasmosaurinae.^[21] Key synapomorphies supporting the placement of Elasmosaurus in Elasmosauridae include an extreme cervical vertebral count exceeding 70, highly elongate cervical centra that contribute to a disproportionately long neck relative to body size, and a reduced skull size comprising less than 10% of total body length. These features distinguish elasmosaurids from other plesiosauromorphs and highlight adaptations for specialized aquatic lifestyles. Elasmosaurids, including Elasmosaurus, originated from earlier plesiosaurs during the Early Jurassic, with the clade undergoing significant diversification and faunal turnover during the Jurassic-Cretaceous transition, ultimately peaking in diversity and morphological disparity during the Late Cretaceous.

Synonymy and invalid species

The genus Elasmosaurus is monospecific, with E. platyurus Cope, 1868, as the type species based on the holotype specimen ANSP 10081 from the Sharon Springs Member of the Pierre Shale Formation in Kansas. All other species originally assigned to the genus have been reclassified as invalid, junior synonyms, or belonging to other genera following extensive taxonomic revisions.^[8] During the late 19th century Bone Wars, intense rivalry between paleontologists Edward Drinker Cope and Othniel Charles Marsh led to hasty descriptions and overassignment of fragmentary plesiosaur remains to Elasmosaurus, resulting in numerous invalid taxa. This taxonomic inflation was addressed in the 20th century through detailed redescriptions, notably by Samuel P. Welles in 1943, who synonymized or reassigned several species, and by Kenneth Carpenter in 1999, who conducted a comprehensive revision of North American elasmosaurs to clarify generic boundaries.^[22]^[23] One such invalid species is Elasmosaurus nobilis Marsh, 1872, based on a partial skeleton (YPM 1640) from the Fort Hays Limestone in Kansas, which is now regarded as a nomen dubium and has been synonymized with Baptanodon or referred to Styxosaurus snowii. Welles (1943) further distinguished E. serpentinus Cope, 1869, as sufficiently different to warrant a new genus, Hydralmosaurus, though subsequent studies have synonymized Hydralmosaurus material with Styxosaurus. These revisions underscore the challenges of working with incomplete Cretaceous marine reptile fossils and the importance of comparative anatomy in resolving synonymies.^[23]

Paleobiology

Locomotion and aquatic adaptations

Elasmosaurus, as an elasmosaurid plesiosaur, propelled itself through the water primarily using its enlarged foreflippers in an underwater flight stroke, akin to that observed in modern sea turtles, while its smaller hindflippers assisted in steering and braking.^[24] This four-flipper locomotion involved synchronous or semi-synchronous flapping motions, where both pairs of flippers generated lift-based thrust through hydrofoil-like actions, optimizing efficiency by leveraging wake vortices from the foreflippers to enhance hindflipper performance.^[25] The foreflippers, being larger and more robust, provided the majority of propulsive force, enabling sustained cruising.^[26] Estimated swimming speeds for Elasmosaurus and similar elasmosaurids were modest, with cruising velocities inferred at 0.5–1 m/s based on flipper aspect ratios and experimental models of plesiosaur kinematics, allowing for efficient long-distance travel in the Western Interior Seaway.^[25] Burst speeds could reach up to 2 m/s during predator evasion or prey pursuit, though such efforts were energetically costly and limited by the animal's body plan.^[27] These speeds reflect adaptations for ambush predation rather than high-speed chasing, consistent with the hydrodynamic constraints of long-necked plesiosaurs.^[28] Buoyancy control in Elasmosaurus was likely achieved through neutral buoyancy facilitated by adjustable lung volume, similar to extant marine reptiles.^[29] As fully aquatic animals incapable of returning to land, elasmosaurids including Elasmosaurus were viviparous, giving birth to live young directly in water to maintain their pelagic lifestyle without terrestrial constraints.^[30] Key aquatic adaptations included hyperphalangy in the flippers, increasing surface area for greater lift generation during strokes, and a streamlined body with a broad, flat torso and short tail to minimize drag. These features collectively enabled effective navigation in open marine environments.^[31]

Neck mobility and foraging behavior

The neck of Elasmosaurus, comprising approximately 72 cervical vertebrae, displayed limited flexibility constrained by the orientation and size of its zygapophyseal facets, which permitted only modest bending at each intervertebral joint. Studies modeling elasmosaur neck motion indicate a mean range of 1–3° per joint, resulting in total lateral flexion of 94–176°, ventral flexion of 75–177°, and dorsal flexion of 87–155°, depending on intervertebral cartilage thickness of 1–3 mm.^[32] These constraints favored vertical over lateral movement posteriorly, enabling a horizontal sweep approaching 180° but precluding extreme postures like a tightly coiled "S-shape."^[32] The zygapophyseal facets, which become more inclined along the neck, further stabilized the structure during swimming while allowing targeted adjustments for prey interception.^[32] Hydrodynamic analyses of plesiosaur necks, including those of elasmosaurids, reveal that elongation does not substantially increase drag during forward locomotion, as water flow remains streamlined over the extended structure.^[33] Consequently, neck undulation likely served for precise positioning and maneuvering rather than contributing to primary propulsion, which was dominated by the four flippers.^[33] Thicker necks, as inferred for Elasmosaurus, minimized turbulence and drag compared to slender configurations, supporting sustained cruising with minimal energetic cost for neck adjustments.^[33] In foraging, Elasmosaurus functioned as an ambush predator, maintaining a straight, horizontal neck for hydrodynamic stealth and camouflage while approaching prey schools, then employing lateral or ventral flexion for rapid strikes.^[32] This strategy exploited the neck's reach—approximately 7 m in length—to target small, agile marine organisms within 5–7 m without repositioning the body, enhancing efficiency in open-water habitats.^[32] Forward-oriented orbits in related elasmosaurids suggest some binocular overlap, aiding depth perception for accurate prey localization during these strikes.^[34] Evolutionarily, the elongated neck represented a trade-off: it expanded foraging range for evasive, small-bodied prey but diminished maneuverability relative to short-necked pliosauromorphs, which prioritized speed for pursuing larger quarry.^[32]

Diet and feeding mechanisms

Elasmosaurus exhibited a primarily piscivorous diet, consisting of small fish such as Enchodus and other small teleost species less than 50 cm in length, along with squid and soft-bodied marine invertebrates. Direct evidence for the diet of Elasmosaurus platyurus is limited due to the scarcity of fossils, with inferences drawn from closely related elasmosaurids.^[35]^[19] There is no evidence indicating consumption of large prey, consistent with the animal's anatomical adaptations for targeting agile, mid-water schoolers rather than larger or heavily armored organisms.^[35] The feeding mechanism of Elasmosaurus involved gape-and-suction capture, where the mouth expanded rapidly to generate suction for drawing in prey, aided by fang-like teeth arranged along the jaws to impale and secure slippery items like fish or cephalopods.^[35] These interlocking, conical teeth, lacking robust crushing surfaces, were ill-suited for hard-shelled prey but effective for holding soft or evasive targets, potentially with assistance from a mobile tongue to manipulate food toward the throat.^[35] Stomach contents from elasmosaurid specimens include disarticulated fish remains—such as vertebrae, scales, and teeth—demonstrating whole-prey ingestion of multiple small individuals, as seen in related elasmosaurids with preserved gut material featuring similar fish bone and scale fragments. Gastroliths recovered in association with these stomach contents suggest post-ingestion mechanical breakdown in a gizzard-like structure, helping to grind bones and aid digestion of the high-volume, low-nutrient small-prey diet while foraging in the mid-water columns of the Western Interior Seaway.^[35] This strategy aligns with the estimated energy demands of a 5–14 m long predator, requiring substantial daily caloric intake from abundant, schooling resources to sustain its active aquatic lifestyle.^[35]

Paleoecology

Geological context and distribution

Elasmosaurus inhabited the Western Interior Seaway during the Campanian stage of the Late Cretaceous period, with a temporal range of approximately 80.6 to 77 million years ago based on ammonite biozonation from Baculites obtusus to Baculites perplexus zones at the type locality.^[36] The holotype specimen of E. platyurus (ANSP 10081) originates from the Sharon Springs Member of the Pierre Shale Formation in Logan County, Kansas, a key stratigraphic unit preserving marine deposits from this interval.^[16] Additional material potentially referable to the genus has been identified in the Pierre Shale of South Dakota and the stratigraphically equivalent Pembina Member in Manitoba, extending its known occurrences across the northern and central portions of the seaway.^[37] The Pierre Shale Formation records sediments deposited in the Western Interior Seaway, a vast epicontinental sea that bisected the North American continent from the Gulf of Mexico to the Arctic Ocean.^[38] Water depths in this region during the Campanian were likely greater than 60 meters (200 feet), creating a relatively shallow marine setting conducive to the accumulation of fine-grained clastic sediments, though depths varied regionally up to several hundred meters in deeper parts of the seaway.^[39] Surface water temperatures averaged around 16–21°C, as determined by clumped isotope analyses of macrofossils from equivalent strata.^[40] High biological productivity in the seaway, driven by nutrient influx from surrounding landmasses and upwelling, resulted in the deposition of organic-rich shales with chalky intervals in the Pierre Shale, reflecting episodes of elevated phytoplankton blooms and subsequent sedimentation.^[41] The distribution of Elasmosaurus remains confined to the Western Interior Seaway, with all verified fossils deriving from North American localities and no confirmed extra-continental records as of 2025.^[42]

Contemporaneous fauna and ecological role

Elasmosaurus inhabited the Western Interior Seaway during the middle Campanian stage of the Late Cretaceous, approximately 80.6–77 million years ago, with its fossils primarily preserved in the Pierre Shale formation, including the Pembina and Sharon Springs members. This epicontinental sea supported a diverse marine vertebrate assemblage, dominated by reptiles adapted to pelagic and neritic environments. Key contemporaneous taxa included mosasaurs such as Tylosaurus proriger, Platecarpus tympanicus, Clidastes propython, and Hainosaurus pembinensis, which ranged from 5 to 15 meters in length and served as apex predators. Other plesiosaurs coexisted, notably polycotylids like Dolichorhynchops osborni (3–6 meters) and elasmosaurids including Styxosaurus snowii and Hydralmosaurus serpentinus. Sharks, such as Squalicorax kaupi and Cretolamna appendiculata, were abundant, alongside sea turtles like Toxochelys latiremis and Protostega sp., and a rich array of teleost fishes, including Enchodus petrosus, Xiphactinus audax, and clupeomorphs. In the northern portions of the seaway, such as the Pembina Member in Manitoba, plesiosaurs exhibited higher relative abundance compared to the southern subprovinces, where sharks and turtles showed greater diversity.^[43]^[44] Birds, particularly hesperornithiforms like Hesperornis regalis, also populated these waters as diving piscivores. The Pierre Shale's anoxic bottom conditions favored exceptional preservation of disarticulated skeletons and isolated elements, reflecting a high-productivity surface ecosystem with evidence of predation and scavenging interactions among these groups. Invertebrates, though not the focus here, included ammonites and belemnites that formed part of the lower trophic levels.^[43]^[44] Ecologically, Elasmosaurus occupied a mid-trophic level predatory niche within this dynamic seaway, functioning as an ambush hunter that targeted small nektonic prey such as schooling fish (Enchodus spp. and clupeomorphs) and possibly cephalopods like ammonites. Stomach contents from associated elasmosaurid specimens reveal ingested Enchodus individuals up to 30 cm long, indicating a diet focused on agile, mid-water organisms seized via its interlocking teeth and maneuverable neck. Gastroliths, totaling up to 6.8 kg in some individuals and sourced from distant terrestrial quartzites, aided in grinding indigestible prey remains in the stomach, suggesting adaptations for processing bony fish. Unlike larger mosasaurs such as Tylosaurus, which preyed on sizable vertebrates including other reptiles, Elasmosaurus posed minimal threat to top predators and likely foraged in open-water habitats, contributing to the seaway's stratified food web during a period of faunal reorganization toward the end of the Cretaceous.^[35]^[35]^[43]

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[30]
Elasmosaur (Reptilia: Sauropterygia) neck flexibility: Implications for ...
Elasmosaurs were extremely long-necked, aquatic reptiles that used four flippers for locomotion. Their distinctive long neck distinguishes them from all ...
[31]
Functional morphology and hydrodynamics of plesiosaur necks
By simulating water flow past the three-dimensional digital plesiosaur models, our results demonstrated that neck elongation does not noticeably affect the ...
[32]
Kaiwhekea katiki, a Late Cretaceous plesiosaur from high southern ...
On the skull of Kaiwhekea, the large forward-looking orbit hints at binocular vision. A large temporal fossa (skull opening) behind the eye indicates large fast ...
[33]
An Elasmosaur with Stomach Contents and Gastroliths from the ...
Sep 22, 2025 · The diet of elasmosauroids and pliosauroids is evidenced by rare fossil stomach contents and the body cavity of some specimens also contains ...
[34]
[PDF] AMERICAN MUSEUM NOVITATES
Sep 23, 2013 · middle to lower upper Campanian, approximately 75 million years ago. ... Baculites obtusus. 80.58 ± 0.552 lower. Baculites sp. (weak flank ...
[35]
(PDF) Sharon Springs Member, Pierre Shale (Lower Campanin)
Mar 13, 2017 · The Sharon Springs Member of the Pierre Shale (lower Campanian) is a black, organically rich shale deposited in the Western lnterior Seaway ...
[36]
[PDF] Paleogeography and the Late Cretaceous of the Western Interior of ...
Roberts, Laura N. Robinson. Paleogeography of the Late Cretaceous of the western interior of middle North. America : coal distribution and sediment ...
[37]
(PDF) Temperature and salinity of the Late Cretaceous Western ...
Sep 14, 2016 · The Western Interior Seaway (WIS) was a shallow (generally <200 m deep) epeiric seaway that covered central North America through most of the ...
[38]
[PDF] Author's personal copy - Harvard University
Temperatures reconstructed for the Late Cretaceous Western Interior Seaway range from 16.473. 5 1C for an offshore Interior Seaway environ- ment from the H. ...
[39]
[PDF] Stratigraphy and Composition of the Sharon Springs Member of the ...
The Pierre Shale, which includes the Sharon. Springs Member at its base, is chiefly a marine medium- to dark-gray noncalcareous shale of Late. Cretaceous age ...
[40]
Taxonomic reassessment of Hydralmosaurus as Styxosaurus
Mar 15, 2016 · The skull length (37.5 cm) and general shape are very alike to KUVP 1301. The 61 cervical vertebrae (59 plus the atlas-axis) are remarkably ...<|control11|><|separator|>
[41]
[PDF] comparative vertebrate taphonomy of the pembina and sharon ...
The Pembina and Sharon Springs members of the Pierre Shale are some of the most organic-rich marine shales in the central portion of the Western Interior. The ...
[42]
Paleobiogeography of the Cretaceous Western Interior Seaway of ...
The Southern Interior Subprovince is characterized by a high diversity in all groups and is dominated by sharks, turtles and the mosasaur Clidastes. These ...Missing: Elasmosaurus | Show results with:Elasmosaurus