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EXHIBIT 210

Elasmosaurus

Elasmosaurus platyurus

Marine reptile

Elasmosaurus platyurus was a long-necked marine reptile from Kansas. Re-examination of its type skeleton identified seventy-two neck vertebrae. [1]

Evidence profile

TWO WAYS TO PICTURE THE PAST

Compare the evidence with the familiar movie image. The illustrations are not to a shared scale.

01 / SOURCE-INFORMED RECONSTRUCTION

A life reconstruction from the evidence

Illustrative life reconstruction of Elasmosaurus in a period-appropriate environment; coloration and missing anatomy are interpretations.

An illustrative reconstruction. Compare its anatomy with the evidence and limitations in the dossier. [1]

Source-informed reconstruction. Appearance evidence [1]. Original illustration; missing anatomy, coloration and scenery include interpretation.

Fossils constrain this life reconstruction. Missing anatomy, coloration and the environmental scene include interpretation; the dossier explains the evidence limits.

02 / MOVIE-STYLE INTERPRETATION

A cinematic imagination

Artistic reconstruction of Elasmosaurus in a marine setting; colors and missing soft tissues are interpretations.

An illustrative reconstruction. Compare its anatomy with the evidence and limitations in the dossier. Lighting, coloration and scenery are artistic choices. This image does not document a fossil locality or behavior.

Original artwork · artistic interpretation.

Scientific view: source-informed reconstruction, credited paleoart or specimen-based imagery. Movie-style view: Original artistic interpretation. Reconstructions involve uncertainty.

PERIODLate Cretaceous[1]
DIETCarnivore (inferred)Evidence and uncertainty in the dossier
TOTAL LENGTHSee the dossierEstimate scope matters
FOSSILS FOUNDUnited States[1]
CompareRead the dossierView the sources

MEET THE ANIMAL

Meet Elasmosaurus

Elasmosaurus platyurus lived in the Late Cretaceous sea that covered part of North America. Its famous Kansas skeleton is a marine reptile, not a dinosaur. The standout feature is its extraordinary neck. A careful re-examination counted seventy-two neck vertebrae, or backbone bones. A separated fossil fragment supplied the evidence that corrected an earlier count. [D1]

The type skeleton is incomplete: much of the backbone remains, while only pieces of the skull survive and the originally described limb girdles are lost. Its pointed teeth suggest animal feeding. Those bones help build a reconstruction, but they do not give a complete preserved body, a measured weight, or a record of every meal the animal ate. [D2]

Plesiosaurs had four swimming paddles, and flipper experiments help test how the pairs could work together. Such models are tests of ideas, rather than videos of Elasmosaurus moving. [D3]

A pregnancy fossil in another plesiosaur provides live-birth evidence for the wider group. It does not show this genus nesting, tell us its litter size, or establish how parents treated their young. [D4]

PREHISTORIC ANIMAL DOSSIER

A life in profile.

The animal, the evidence, and the questions still open.

The type preserves much of the vertebral column but only parts of the skull, and its originally described limb girdles are now lost. A complete silhouette combines surviving bones and restoration. [D2]

Profile scope: Genus Elasmosaurus; E. platyurus, incomplete holotype ANSP 10081. This genus is not interchangeable with the elasmosaur family or every restored long-necked marine skeleton. [D1]

Time
Late Cretaceous
Fossil locations in this exhibit
United States
How to read the evidence

Source supported identifies a description documented by the cited source. Inferred marks a reconstruction or functional estimate. Debated marks competing interpretations. Not established means the sources reviewed for this dossier do not support a firm conclusion; it does not mean a behavior never occurred.

A size reference is an estimate, not a population range. Nesting evidence does not by itself establish courtship, mate choice, or lifelong pairing.

Body length

Not established

Not established here

The type is incomplete and restoration depends on missing parts. Its neck-bone count does not independently measure an intact living animal. [D2]

Body mass

Not established

Not established here

Partial cranial material and lost girdles do not supply measured mass. No reproducible individual estimate was adopted. [D2]

Diet

Inferred

Animal feeding inferred from teeth

Jaw fragments bear pointed teeth suited to seizing prey. A specific menu is not established by a meal with this holotype. [D2]

Habitat & fossil setting

Source supported

Lower Campanian Western Interior sea

ANSP 10081 came from western Kansas’s marine Sharon Springs Formation. [D1]

Movement

Inferred

Four-paddle swimming reconstructed

Plesiosaur models support propulsion by both pairs, not an Elasmosaurus stroke, speed or habitual neck pose. [D3]

Distinctive anatomy

Source supported

Seventy-two cervical vertebrae

Rediscovered material revised seventy-one to seventy-two; vertebral fusion indicates skeletal maturity, not breeding age. [D1]

Reproduction & life together

Reproduction & nesting

Inferred

Live birth is a broader-group inference

A pregnancy fossil belongs to another plesiosaur. Applying live birth to Elasmosaurus remains comparison, not an observed genus pregnancy. [D4]

Courtship & mating

Not established

Not established here

The plesiosaur synthesis does not establish mating displays or sexual dimorphism for Elasmosaurus. [D5]

Social behavior

Not established

Not established here

The synthesis leaves parental care and sociality unresolved; a long neck does not establish schooling or cooperation. [D5]

Dossier research & sources

Sources and inspection notes for the claims in this profile.

  1. Revised Vertebral Count in the “Longest-Necked Vertebrate” Elasmosaurus platyurus Cope 1868, and Clarification of the Cervical-Dorsal Transition in PlesiosauriaPLOS ONE; Sachs, Kear & Everhart (2013) · Accessed 2026-10-05Full original text inspected: ANSP 10081, rediscovered bone, seventy-two cervicals, mature fusion, Lower Campanian Sharon Springs Formation and historical head-on-tail correction. Bone maturity is not breeding age. · Inspected: page
  2. Redescription of Elasmosaurus platyurus Cope 1868 (Plesiosauria: Elasmosauridae) from the Upper Cretaceous (Lower Campanian) of Kansas, U.S.A.Paludicola; Sven Sachs (2005), author-hosted original PDF · Accessed 2026-10-05Original sixteen-page PDF inspected: partial skull, type material, teeth and lost girdles. Seventy-one cervical count superseded by 2013; historical total-body estimates not adopted as measured adult dimensions. · Inspected: page
  3. The four-flipper swimming method of plesiosaurs enabled efficient and effective locomotionProceedings of the Royal Society B; Muscutt et al. (2017), University of Bristol record · Accessed 2026-10-05Original abstract and introduction inspected through institutional record and PMC text. Water-tank models test interacting flippers; no observed genus gait or speed claimed. · Inspected: abstract
  4. Viviparity and K-selected life history in a Mesozoic marine plesiosaur (Reptilia, Sauropterygia)Science; O’Keefe & Chiappe (2011), PubMed · Accessed 2026-10-05Complete indexed abstract inspected. Fetus inside a Late Cretaceous adult supplies live-birth evidence there. Extension to these genera and social/parent-care proposals remain hypotheses; abstract does not name the fossil genus. · Inspected: abstract
  5. PlesiosaursCurrent Biology; P. Martin Sander (2023) · Accessed 2026-10-05Publisher-indexed life-history/macropredator sections inspected, including explicit limits on parental care, sexual dimorphism, social behavior and migration. Direct publisher opening failed; complete article/figure inspection not claimed. · Inspected: excerpt

THE STORY IN THE FOSSILS

One misplaced head, one rediscovered bone.

Cope placed the head at the wrong end. The documented correction was Leidy’s, rather than the often repeated attribution to Marsh. [1]

Matching a separated half vertebra to its partner revised the neck count without discovering another animal. [1]

A note on scale and time

The dossier identifies the scope of each reference estimate. A mount, an individual fossil and a species-wide adult range are different measurements. Comparison metrics remain unavailable where adult scope has not been established. Unknown does not mean zero.

Sources & editorial notes

Sources support the stated claims and scopes. Refer to the evidence notes for uncertainty.

  1. Revised Vertebral Count in the “Longest-Necked Vertebrate” Elasmosaurus platyurus Cope 1868, and Clarification of the Cervical-Dorsal Transition in PlesiosauriaPLOS ONE; Sachs, Kear & Everhart (2013) · Accessed 2026-10-05Full original text inspected: ANSP 10081, rediscovered bone, seventy-two cervicals, mature fusion, Lower Campanian Sharon Springs Formation and historical head-on-tail correction. Bone maturity is not breeding age. · Inspected: page
  2. Redescription of Elasmosaurus platyurus Cope 1868 (Plesiosauria: Elasmosauridae) from the Upper Cretaceous (Lower Campanian) of Kansas, U.S.A.Paludicola; Sven Sachs (2005), author-hosted original PDF · Accessed 2026-10-05Original sixteen-page PDF inspected: partial skull, type material, teeth and lost girdles. Seventy-one cervical count superseded by 2013; historical total-body estimates not adopted as measured adult dimensions. · Inspected: page
  3. The four-flipper swimming method of plesiosaurs enabled efficient and effective locomotionProceedings of the Royal Society B; Muscutt et al. (2017), University of Bristol record · Accessed 2026-10-05Original abstract and introduction inspected through institutional record and PMC text. Water-tank models test interacting flippers; no observed genus gait or speed claimed. · Inspected: abstract
  4. Viviparity and K-selected life history in a Mesozoic marine plesiosaur (Reptilia, Sauropterygia)Science; O’Keefe & Chiappe (2011), PubMed · Accessed 2026-10-05Complete indexed abstract inspected. Fetus inside a Late Cretaceous adult supplies live-birth evidence there. Extension to these genera and social/parent-care proposals remain hypotheses; abstract does not name the fossil genus. · Inspected: abstract
  5. PlesiosaursCurrent Biology; P. Martin Sander (2023) · Accessed 2026-10-05Publisher-indexed life-history/macropredator sections inspected, including explicit limits on parental care, sexual dimorphism, social behavior and migration. Direct publisher opening failed; complete article/figure inspection not claimed. · Inspected: excerpt

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