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CretaceousherbivoreFossil completeness: good

Amargasaurus cazaui

Pronunciation: ah-MAR-gah-SORE-us kaz-OW-eye

A small, short-necked Patagonian sauropod whose paired cervical neural spines formed one of the most extraordinary silhouettes in dinosaur evolution.

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Amargasaurus cazaui

The page URL and title are included automatically. Optional contact details are used only to discuss this report. Do not submit private information or precise sensitive fossil-site coordinates.

Last updated 16 July 2026

Pair of Amargasaurus cazaui in a display reconstruction by Fred WierumArt by Fred Wierum · CC BY-SA 4.0

Field guide

Overview

Amargasaurus cazaui was a dicraeosaurid sauropod from the Early Cretaceous of Neuquén Province, Argentina. At roughly nine metres long it was modest beside giant sauropods, with a relatively short neck, low skull and compact body. Its paired neural spines lengthened dramatically along the neck and front of the back, in some positions reaching about four times the height of the vertebral centrum. Those bones certainly supported substantial soft tissue, but fossils do not preserve the living outline, leaving competing reconstructions as two sails, a single padded crest or another continuous covering.

Its fossils occur between approximately 130 and 123 million years ago. Values shown here are approximate and reflect the current curated seed dataset.

Form and function

Anatomy

Holotype MACN PV N15 preserves part of the skull, a nearly continuous articulated series of 22 vertebrae before the sacrum, the sacrum, part of the tail, shoulder and pelvic elements, and portions of all four limbs. The skull was low and horse-like, with pencil-shaped teeth concentrated toward the front of the jaws. Each neck vertebra carried paired, deeply divided neural spines that became extremely tall and inclined backward. The back also bore elongated paired spines, while the neck itself was shorter and the body smaller than in most familiar sauropods.

  • Paired hyperelongate neural spines along the neck
  • Elongated divided spines continuing onto the front of the back
  • Relatively short neck for a sauropod
  • Low skull with narrow pencil-like teeth
  • Compact body and moderate adult size
  • Nearly continuous articulated presacral vertebral series

Evolutionary position

Scientific classification

  1. 1Dinosauriaclade
  2. 2Saurischiaclade
  3. 3Sauropodomorphaclade
  4. 4Sauropodaclade
  5. 5Diplodocoideasuperfamily
  6. 6Dicraeosauridaefamily
  7. 7Amargasaurusgenus
  8. 8Amargasaurus cazauispecies

This simplified classification path shows one placement from Dinosauria to this species. Each step is clickable, and other analyses may support alternative relationships.

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Scale

Size comparison

Scientific record

Discovery and naming

Geologist Luis Cazau alerted José Bonaparte's team to the fossil potential of the La Amarga Formation. During a February 1984 expedition led by Bonaparte, Guillermo Rougier discovered the associated skeleton near La Amarga stream at the foot of China Muerta hill. Leonardo Salgado and Bonaparte formally named Amargasaurus cazaui in 1991, honouring both the formation and Cazau. An informal 1984 mention used the name Amargasaurus groeberi, but it was not a valid published species name. The holotype remains the principal source for the animal's anatomy.

Discovery credit: Guillermo Rougier, José F. Bonaparte, Luis Cazau.

Naming authors: Leonardo Salgado, José F. Bonaparte.

Palaeoenvironment

Habitat and behaviour

The lower La Amarga Formation records braided rivers, lakes, floodplains and developing soils in the Neuquén Basin. Seasonal conditions supported conifers, cycads, ferns and other vegetation. The wider fauna included several kinds of sauropod, the small theropod Ligabueino, crocodyliforms and the mammal Vincelestes. Finds distributed through different members of the formation did not all live at exactly the same time.

The narrow teeth and relatively small skull indicate selective cropping rather than oral grinding; swallowed vegetation was processed in the digestive system. Tall paired spines almost certainly made the neck visually prominent and may have supported display tissue, but no fossil reveals colour, sex differences or display behaviour. Bone microstructure published in 2022 does not support simply treating each spine as the core of a long independent keratin horn. Defensive use, thermoregulation and species recognition remain possibilities rather than demonstrated functions.

Worth knowing

Field notes

  • Some neck spines were approximately four times as tall as the vertebral bodies supporting them.
  • Its nearly complete neck remained articulated to the skull and sacrum when found.
  • The species honours geologist Luis Cazau, who guided the expedition toward the fossil-rich formation.
  • Amargasaurus was only about half the length of many famous diplodocid sauropods.

Fossil distribution

Fossil locations

La Amarga stream type regionLa Amarga stream type region, Neuquén Province, Argentina
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La Amarga stream type region

Neuquén Province, Argentina

La Amarga Formation, Puesto Antigual Member

regional marker

Markers are deliberately approximate. They identify published fossil areas without exposing sensitive excavation coordinates.

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Fossil specimen record

Museums and research collections

Museo Argentino de Ciencias Naturales Bernardino Rivadavia

verified

Buenos Aires, Argentina

Repository of the original partial skull and associated skeleton that define Amargasaurus cazaui. This entry identifies the research collection and does not claim that the fragile holotype is currently mounted for public display.

Record type: originalChecked 16 July 2026Institution website

A research repository is not necessarily a public exhibit. Loan and display status can change, so check with the institution before visiting.

Scientific uncertainty

  • No skin impression preserves the external profile of the paired neck spines.
  • Reconstructions as separate horns, paired sails, one continuous sail or a padded crest remain debated.
  • The holotype is the only diagnostic skeleton, so individual variation is largely unknown.
  • Published body masses vary because the torso and missing limb portions require reconstruction.
  • Display behaviour and sexual differences are plausible but not directly evidenced.

Evidence

References and sources

  1. 01
    Un nuevo saurópodo Dicraeosauridae, Amargasaurus cazaui gen. et sp. nov., de la Formación La Amarga

    Leonardo Salgado, José F. Bonaparte · Ameghiniana 28(3–4) · 1991

    Open source
  2. 02
    Osteohistology of the hyperelongate hemispinous processes of Amargasaurus cazaui

    Ignacio A. Cerda, Fernando E. Novas, José Luis Carballido, Leonardo Salgado · Journal of Anatomy 240(6) · 2022

    Open source
  3. 03
    Museo Argentino de Ciencias Naturales Bernardino Rivadavia

    MACN-CONICET

    Open source