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EXHIBIT 146

Anchisaurus

Anchisaurus polyzelus

Anchisaurus was a small North American sauropodomorph whose juvenile and mature skulls reveal changes during growth. [3]

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 / SKELETAL RECONSTRUCTION

A framework from the fossils

Historical drawing of the right hindfoot formerly identified as Anchisaurus major.

Marsh’s 1889 drawing of a right hindfoot, originally Anchisaurus major and later Ammosaurus major. The 2010 revision includes this historical species under Anchisaurus polyzelus. This is a foot, not a hand, and is not the YPM 1883 mass-reference individual. [3]

Historical hindfoot of Anchisaurus major · O. C. Marsh (1889). Public domain. Resized proportionally and converted to WebP; no anatomical edits. Same source license applies.

Skeletal mounts and drawings may restore missing parts; the caption identifies the displayed material.

02 / MOVIE-STYLE INTERPRETATION

A cinematic imagination

Artistic reconstruction of Anchisaurus; colors and soft tissues are illustrative.

Original cinematic interpretation with the forelimbs raised for the displayed pose and an enlarged medial thumb claw. Habitual stance is uncertain: functional analyses differ, including a quadrupedal interpretation. Colors, soft tissues and setting are artistic. 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.

PERIODEarly Jurassic[1]
DIETHerbivoreEvidence and uncertainty in the dossier
TOTAL LENGTHSee the dossierEstimate scope matters
FOSSILS FOUNDUnited States[1]
CompareRead the dossierView the sources

MEET THE ANIMAL

Meet Anchisaurus

Anchisaurus was a small plant-eating dinosaur from Early Jurassic North America. It belonged to the wider dinosaur group that includes the giant sauropods, although the museum's general length reference is only about two metres. That reference is not linked to a particular growth stage. It describes a reconstructed scale, rather than the largest possible mature Anchisaurus. [D6]

Two skulls from Connecticut helped researchers investigate how its head changed as it grew. They used micro-CT scans, a form of X-ray imaging, to build three-dimensional models. The young animal and the adult did not have identical skull shapes. Comparing individuals at different ages helps separate developmental changes from differences that might otherwise be mistaken for separate species. [S1]

This growth comparison also contributes to a larger evolutionary question. Later sauropods developed some distinctive head features earlier in their lives than Anchisaurus did. Changes in the timing of development can therefore help explain how dinosaur bodies evolved. The study concerns the formation of skulls, not a direct record of nesting, family life or the age when an individual first reproduced. [S1]

Overview sources
  1. A sauropod skull story — the long versionYale University; Jim Shelton (2021) · Accessed 2026-10-04Inspected: page

PREHISTORIC ANIMAL DOSSIER

A life in profile.

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

CT and histology reveal head growth. Its usual walking stance has competing interpretations. [D3] [D5]

Profile scope: Genus profile centered on Anchisaurus polyzelus. YPM 1883 is the designated neotype; larger YPM 208 and young YPM 209 are separate referred individuals. [D2] [D1]

Time
Early Jurassic
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

Inferred

About 2 m; museum reference

The museum supplies a whole-body reference without specimen, stage or method. Larger referred individuals are known, so this reference is not an adult maximum or a genus-wide range. [D6] [D1]

Body mass

Inferred

About 20 kg; newly mature neotype model

Paul’s volume-scaled reconstruction estimates YPM 1883. Independent histology identifies that individual as having just reached somatic maturity; body restoration and density retain uncertainty. [D4] [D3]

Diet

Inferred

Plants

The museum identifies herbivory. CT evidence shows anterior teeth projecting forward more strongly in the mature individual, but does not identify its precise food plants or daily intake. [D6] [D3]

Habitat & fossil setting

Source supported

Early Jurassic northeastern United States

Reviewed material includes Springfield, Massachusetts, and Manchester, Connecticut. The articulated Manchester skeletons come from the Portland Formation, assigned a Pliensbachian age in the revision. [D1]

Movement

Inferred

Walking stance remains debated

A limb-proportion classifier favors quadrupedality but gives weaker support than for other sampled transitional taxa. Earlier anatomical reconstructions favored bipedality; neither demonstrates an observed living stance. [D5]

Distinctive anatomy

Source supported

Head shape changes during growth

The mature skull has a longer snout, more retracted nostrils and more projecting front teeth than YPM 209. CT-restored skulls include reconstructed missing margins; they are not intact undistorted originals. [D3]

Reproduction & life together

Reproduction & nesting

Not established

Not established here

Histology distinguishes a young individual from a newly somatically mature one. Somatic maturity does not establish reproductive maturity, eggs, nest layout or parental care. [D3]

Courtship & mating

Not established

Not established here

Developmental skull differences do not identify sexes or mating displays. Focused searches did not establish calls, mate choice or courtship. [D3]

Social behavior

Not established

Not established here

Several separate skeletons came from the Manchester quarry. The reviewed taxonomic study does not establish a persistent herd or family group from that association. [D1]

Dossier research & sources

Sources and inspection notes for the claims in this profile.

  1. A revision of the problematic sauropodomorph dinosaurs from Manchester, Connecticut and the status of Anchisaurus MarshPalaeontology; Yates (2010) · Accessed 2026-10-02Original publisher full text inspected: conspecific Manchester skeletons, historical names, diagnostic pelvis, Portland Formation and Pliensbachian scope. · Inspected: page
  2. Opinion 2361: Anchisaurus Marsh, 1885—usage conserved by designation of a neotypeBulletin of Zoological Nomenclature; International Commission on Zoological Nomenclature (2015) · Accessed 2026-10-02Original two-page ruling inspected: YPM 1883 replaces the fragmentary original type and conserves the name. · Inspected: excerpt
  3. A shift in ontogenetic timing produced the unique sauropod skullEvolution; Fabbri and colleagues (2021), author-deposited accepted paper · Accessed 2026-10-02Original 24-page accepted paper inspected, especially pp7–9: young YPM 209 has three growth marks; YPM 1883 has six humeral/nine rib marks and rib EFS, indicating newly reached somatic maturity. · Inspected: excerpt
  4. Appendix: dinosaur massesPrinceton University Press; Paul (2016) · Accessed 2026-10-02Original published appendix and methods inspected: YPM 1883 volume-scaled model 20 kg; not a population measurement. · Inspected: excerpt
  5. A giant dinosaur from the earliest Jurassic of South Africa and the transition to quadrupedality in early sauropodomorphsCurrent Biology; McPhee and colleagues (2018), Oxford accepted paper with appendices · Accessed 2026-10-02Original 57-page accepted paper inspected: Table S3 0.689 quadrupedal posterior probability; STAR Methods distinguishes neotype stance inputs from larger YPM 208 mass inputs. · Inspected: excerpt
  6. AnchisaurusNatural History Museum, London · Accessed 2026-10-02Museum reference inspected: 2.0 m unspecified whole-body size and herbivory. · Inspected: page

THE STORY IN THE FOSSILS

Meet Anchisaurus.

The young and mature skulls provide a developmental comparison. Their differences indicate growth rather than identifying sexes. [3]

The nomenclatural ruling made YPM 1883 the neotype, replacing fragmentary earlier material. Its former name, Anchisaurus colurus, therefore does not receive a separate exhibit. [2]

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. A revision of the problematic sauropodomorph dinosaurs from Manchester, Connecticut and the status of Anchisaurus MarshPalaeontology; Yates (2010) · Accessed 2026-10-02Original publisher full text inspected: conspecific Manchester skeletons, historical names, diagnostic pelvis, Portland Formation and Pliensbachian scope. · Inspected: page
  2. Opinion 2361: Anchisaurus Marsh, 1885—usage conserved by designation of a neotypeBulletin of Zoological Nomenclature; International Commission on Zoological Nomenclature (2015) · Accessed 2026-10-02Original two-page ruling inspected: YPM 1883 replaces the fragmentary original type and conserves the name. · Inspected: excerpt
  3. A shift in ontogenetic timing produced the unique sauropod skullEvolution; Fabbri and colleagues (2021), author-deposited accepted paper · Accessed 2026-10-02Original 24-page accepted paper inspected, especially pp7–9: young YPM 209 has three growth marks; YPM 1883 has six humeral/nine rib marks and rib EFS, indicating newly reached somatic maturity. · Inspected: excerpt
  4. Appendix: dinosaur massesPrinceton University Press; Paul (2016) · Accessed 2026-10-02Original published appendix and methods inspected: YPM 1883 volume-scaled model 20 kg; not a population measurement. · Inspected: excerpt
  5. A giant dinosaur from the earliest Jurassic of South Africa and the transition to quadrupedality in early sauropodomorphsCurrent Biology; McPhee and colleagues (2018), Oxford accepted paper with appendices · Accessed 2026-10-02Original 57-page accepted paper inspected: Table S3 0.689 quadrupedal posterior probability; STAR Methods distinguishes neotype stance inputs from larger YPM 208 mass inputs. · Inspected: excerpt
  6. AnchisaurusNatural History Museum, London · Accessed 2026-10-02Museum reference inspected: 2.0 m unspecified whole-body size and herbivory. · Inspected: page

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