Amargasaurus cazaui

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.

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

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.

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.

• 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.

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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