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EXHIBIT 173

Stegouros

Stegouros elengassen

Stegouros was a small armored plant eater with a short tail ending in a flattened blade-like weapon. [2]

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

CT-based reconstruction of Stegouros elengassen tail weapon and its distal vertebrae.

Author-preprint figure 2 reconstructs the tail weapon of S. elengassen CPAP-3165 from CT segmentation. Analytical colors distinguish bones, rather than living pigmentation; the distal fused blade differs from an ankylosaurid knob. Living colors and soft tissues are unknown. [1]

Stegouros tail.jpg · Sergio Soto-Acuña, Alexander Vargas, Jonatan Kaluza, Marcelo Leppe, Joao Botelho, José Palma-Liberona, Carolina Gutstein, Roy Fernández, Hector Ortiz, Verónica Milla, Bárbara Aravena, Leslie Manríquez, Jhonatan Alarcón-Muñoz, Juan Pino, Christine Trevisan, Héctor Mansilla, Luis Hinojosa, Vicente Muñoz-Walther and David Rubilar-Rogers. CC BY 4.0. Proportional resizing and WebP conversion; no anatomy edits.

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

02 / MOVIE-STYLE INTERPRETATION

A cinematic imagination

Illustrative reconstruction of Stegouros elengassen; colors, soft tissues and missing anatomy remain interpretive.

Original cinematic interpretation of Stegouros. The short tail and flattened lateral blade weapon are fossil-guided; complete skin, scute positions, colors and living pose remain interpretive. Colors, lighting and scenery are artistic choices; this is not directly observed behavior. 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]
DIETHerbivoreEvidence and uncertainty in the dossier
TOTAL LENGTHSee the dossierEstimate scope matters
FOSSILS FOUNDMagallanes, Chile[1]
CompareRead the dossierView the sources

MEET THE ANIMAL

Meet Stegouros

Stegouros was an armored dinosaur from Late Cretaceous Patagonia in Chile. Its genus name means 'roofed tail,' while the species name, elengassen, refers to an armored monster in Aonik'enk tradition. The name links a scientific discovery to the region's cultural history, rather than claiming that the dinosaur itself was the creature described in a legend. [S1]

The research team identified it as a plant eater in a southern landscape with rivers, forest vegetation and ferns. Its tail had an unusual flattened weapon, unlike the familiar rounded clubs of some northern ankylosaurs. The discovery adds a distinctive southern armored body plan without showing the exact plants eaten or a particular defensive encounter. [D2]

Seven pairs of lateral bony plates encased the tail's rear half. The final five pairs fused into a flat, lobed structure; the first two pairs remained separate. [D1]

Later fieldwork announced additional Stegouros remains. Those discoveries expand the material available for future study, but the report does not establish a herd, family group or nesting colony. More fossils can improve a profile without immediately resolving every behavioral question. [D3]

Overview sources
  1. Presentación de nueva especie de dinosaurio chilenoUniversidad de Chile; written introduction to2021research presentation · Accessed 2026-10-04Inspected: excerpt

PREHISTORIC ANIMAL DOSSIER

A life in profile.

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

Seven paired lateral osteoderms form the tail weapon. The last five pairs fuse into a flattened frond, distinct from a rounded ankylosaurid club. [D1]

Profile scope: S. elengassen, chiefly CPAP-3165 from the Dorotea Formation: one informative published skeleton, with later field discoveries announced. [D1] [D3]

Time
Late Cretaceous
Fossil locations in this exhibit
Magallanes, Chile
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.

Length

Inferred

About 1.5–1.65 m; revised digital reconstruction

The original 1.8–2 m estimate was revised in a public author comment after digital assembly. This is not a peer-reviewed species range. [D1]

Body mass

Inferred

About 35 kg; illustrated reference

The 2026 publisher sample gives this educational estimate without an individual-specific method or maturity demonstration; excluded from adult comparison. [D4]

Diet

Inferred

Plant eater

The research team identifies herbivory. Regional forest plants were possible foods, not preserved gut contents proving a specific menu. [D2]

Time and habitat

Source supported

Late Cretaceous austral river delta

Río Las Chinas fossils occur in the lower Dorotea succession. The institutional account describes winding rivers, forest vegetation and ferns. [D2]

Locomotion

Inferred

Four-legged, with relatively slender limbs

The description contrasts its limbs with bulkier ankylosaurs. Hoof-like manual unguals support a walking reconstruction, not a measured running speed. [D1]

Distinctive anatomy

Source supported

Short tail with a fused distal blade

The first two osteoderm pairs remain separate; the distal five join into a flat lobed structure, unlike an ankylosaurid knob. [D1]

Reproduction & life together

Reproduction and nesting

Not established

Not established here

Bone fusion excludes an early juvenile interpretation, but does not establish breeding maturity, sex, egg number or nest type. [D1]

Courtship and mating

Not established

Not established here

Calling its tail a weapon does not demonstrate courtship display, sex differences or reproductive combat in this genus. [D2]

Social behavior

Not established

Not established here

Later fieldwork announced more Stegouros remains; the report does not establish a herd, family group or nesting colony. [D3]

Dossier research & sources

Sources and inspection notes for the claims in this profile.

  1. Bizarre tail weaponry in a transitional ankylosaur from subantarctic ChileNature; Soto-Acuña and colleagues (2021) · Accessed 2026-10-02Original abstract/figures, published 49-page supplement and full author preprint inspected. CPAP-3165 tail fusion and maturity indicators; published main text paywalled. Author’s 3December public comment revises digital length to 1.5–1.65 m (printed cm is an obvious unit typo); not a peer-reviewed measurement. Comment location: https://www.nature.com/articles/s41586-021-04147-1#comments ; Alexander O. Vargas Milne, 3 December 2021, independently read on the original publisher page before later cookie redirects. · Inspected: excerpt
  2. U. de Chile presenta al mundo una nueva especie de dinosaurio acorazado con una extraña arma en su colaUniversidad de Chile; Cristian Fuentes Valencia (1 December 2021) · Accessed 2026-10-02Original institutional scientist account inspected: herbivory, Río Las Chinas discovery, austral delta/forest setting and tail weapon. Original roughly 2 m length preceded author correction. · Inspected: page
  3. Investigadores de la U. de Chile descubren nuevos registros de dinosaurios en la PatagoniaUniversidad de Chile (2022) · Accessed 2026-10-02Institutional field report inspected: additional Stegouros remains announced without a published conspecific herd, nesting association or quantified specimen description. · Inspected: page
  4. The Princeton Encyclopedia of Dinosaurs: OrnithischiansPrinceton University Press; Bryce Jones, illustrated by Egidio Viola (2026) · Accessed 2026-10-02Official publisher sample p 65 inspected:2 m and 35 kg illustrated reference. No disclosed specimen-specific mass method; length not substituted for the author’s digital refit. · Inspected: page

THE STORY IN THE FOSSILS

Meet Stegouros

Excavators recovered a block whose rear skeleton remained articulated, including its distinctive tail. The incomplete front and well-preserved rear require different degrees of restoration in a whole-animal illustration. [2]

The discovery team proposed a southern ankylosaur lineage named Parankylosauria. This is an anatomical evolutionary hypothesis, not evidence that geographically separated armored dinosaurs shared behavior. [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. Bizarre tail weaponry in a transitional ankylosaur from subantarctic ChileNature; Soto-Acuña and colleagues (2021) · Accessed 2026-10-02Original abstract/figures, published 49-page supplement and full author preprint inspected. CPAP-3165 tail fusion and maturity indicators; published main text paywalled. Author’s 3December public comment revises digital length to 1.5–1.65 m (printed cm is an obvious unit typo); not a peer-reviewed measurement. Comment location: https://www.nature.com/articles/s41586-021-04147-1#comments ; Alexander O. Vargas Milne, 3 December 2021, independently read on the original publisher page before later cookie redirects. · Inspected: excerpt
  2. U. de Chile presenta al mundo una nueva especie de dinosaurio acorazado con una extraña arma en su colaUniversidad de Chile; Cristian Fuentes Valencia (1 December 2021) · Accessed 2026-10-02Original institutional scientist account inspected: herbivory, Río Las Chinas discovery, austral delta/forest setting and tail weapon. Original roughly 2 m length preceded author correction. · Inspected: page
  3. Investigadores de la U. de Chile descubren nuevos registros de dinosaurios en la PatagoniaUniversidad de Chile (2022) · Accessed 2026-10-02Institutional field report inspected: additional Stegouros remains announced without a published conspecific herd, nesting association or quantified specimen description. · Inspected: page
  4. The Princeton Encyclopedia of Dinosaurs: OrnithischiansPrinceton University Press; Bryce Jones, illustrated by Egidio Viola (2026) · Accessed 2026-10-02Official publisher sample p 65 inspected:2 m and 35 kg illustrated reference. No disclosed specimen-specific mass method; length not substituted for the author’s digital refit. · Inspected: page

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