Amargasaurus cazaui

Amargasaurus lived during the Barremian-Aptian (~129-122 Ma) in what is now the Argentine Patagonia (Neuquén). The La Amarga Formation was dominated by fluvial systems with braided rivers, swamps, and paleosols developed under semi-arid to subhumid conditions. Associated fauna included other sauropods (Zapalasaurus, Amargatitanis), ceratosaurs (Ligabueino), the crocodylomorph Amargasuchus, and the mammal Vincelestes, indicating a diverse riparian forest ecosystem.

Neuroanatomical analyses (Carabajal et al., 2014) and craniocervical musculature studies (Militello et al., 2026) indicate Amargasaurus was a mid-height browser. With its habitual snout position at only 80 cm above ground and a maximum reach of 2.7 m, it specialized in low to intermediate vegetation: ferns, cycads, and small conifers. This strategy reduced competition with other sauropods in the La Amarga Formation that browsed at different heights.

There is no direct evidence of gregarious behavior in Amargasaurus, but the cervical skin sail, supported by the neural spines, likely played a role in intraspecific recognition, social hierarchy, or mate selection. The intense vascularization of the spines (Cerda et al., 2022) suggests the structure was metabolically active. Histological studies indicate the holotype was a young adult at least 10 years old, still growing when it died.

Bone histology of Amargasaurus (Windholz and Cerda, 2021) reveals highly vascularized fibrolamellar bone with cyclical growth marks (LAGs), consistent with an intermediate metabolism between reptiles and full endotherms, with seasonality. The holotype individual grew rapidly in early stages and decelerated progressively. The neural spines are bony with fibrolamellar cortical bone, indicating rapid-growth structures typical of vertebrates with high metabolic demands.

Foundational paper that formally described Amargasaurus cazaui, published in Ameghiniana 28(3-4):333-346. Salgado and Bonaparte described holotype MACN-N 15, collected in 1984 by Guillermo Rougier. The study placed the species within Dicraeosauridae, with exceptionally long bifurcated neural spines as its main autapomorphy. Comparison with Jurassic African Dicraeosaurus hansemanni showed Amargasaurus to be more derived, with even more elongated and bifurcated presacral spines and longer basipterygoid processes.

Skeletal reconstruction of holotype MACN-N 15 by Gunnar Bivens (2024), with known bones shown in white, indicating an estimated total length of 13.34 m.

Photographs and reconstructions of cervical vertebrae of Amargasaurus cazaui, published in Acta Palaeontologica Polonica (2007), showing the double neural spines and internal pneumatic cavities.

Published in Ameghiniana 29(4):337-346, this study deepened the analysis of Amargasaurus's partial skull, describing the temporal and basicranial regions of holotype MACN-N 15. Salgado and Calvo detailed the unusually long basipterygoid processes and cranial proportions that distinguish Amargasaurus from other dicraeosaurids. The work laid the foundation for subsequent studies on head posture and feeding behavior.

Cross-section diagram of Amargasaurus cervical vertebrae, showing internal pneumatic cavities and spine anatomy, published in Acta Palaeontologica Polonica (2007).

Skeletal mount of Amargasaurus cazaui in a museum setting, displaying the articulated vertebral column and the double neural spines that define the species.

This seminal paper proposed that the elongated neural spines of dinosaurs like Amargasaurus supported not a thin skin sail but a denser soft-tissue structure similar to the hump of modern bison. Bailey presented biomechanical analysis and comparisons with extant ungulates, arguing the hump would be more functional for thermoregulation and energy storage. The alternative hump hypothesis influenced decades of debate about the function of Amargasaurus spines.

Size comparison of the three main dicraeosaurids: Amargasaurus (left), Dicraeosaurus (center), and Brachytrachelopan (right), illustration by Nobu Tamura. Amargasaurus has the longest cervical spines in the group.

Neural spine sail variation across different dinosaurian clades, including Amargasaurus (upper right). The panel compares spine morphology in Acrocanthosaurus, Amargasaurus, Spinosaurus, Limaysaurus, Ichthyovenator, and Ouranosaurus.

Published in Acta Palaeontologica Polonica 52(1):167-188, this study reconstructed the axial soft-tissue system of Amargasaurus and other diplodocoids using comparative morphology with crocodilians and birds. The authors determined that the distribution of external pneumatic structures is similar between diplodocids and dicraeosaurids. The analysis identified supravertebral pneumatic diverticula and an elaborate ligament system connecting the cervical spines, supporting the sail hypothesis.

Artistic reconstruction of Amargasaurus cazaui by Nobu Tamura (2008), showing the double spines of the neck and back. At the time, this represented the canonical interpretation of the spines as independent structures.

Reconstruction of Amargasaurus cazaui using mixed technique (felt pens and liquid chalk on parchment) by Pedro Salas (2014), depicting the animal in a ground-level feeding posture.

Published in Gondwana Research 12:533-546, this work inventoried the remarkable diversity of sauropods from the La Amarga Formation. Apesteguía identified isolated bones from dicraeosaurids (including Amargasaurus), rebbachisaurids (Zapalasaurus), basal titanosaurs, and new materials revealing additional clades. The coexistence of multiple sauropods suggests feeding-niche partitioning, with different browsing heights reducing competition among species.

Amargasaurus cazaui fossil specimen at the Museo Paleontológico Egidio Feruglio (MEF) in Trelew, Argentina, one of the main research centers for Patagonian dinosaurs.

Skeletal mount of Amargasaurus cazaui on display at the Museo Paleontológico Egidio Feruglio (MEF), Trelew, Argentina, showcasing the impressive profile of the cervical and dorsal spines.

Published in the Zoological Journal of the Linnean Society 161(4):872-915, this study provided one of the most comprehensive phylogenetic analyses of Diplodocoidea, including Amargasaurus cazaui. Whitlock recovered Suuwassea as a basal dicraeosaurid (the only Laurasian member) and identified two distinct rebbachisaurid clades. The work established important relationships between South American and African dicraeosaurids, providing biogeographic context for the origin and dispersal of Amargasaurus's group.

Neosauropod cladogram showing phylogenetic relationships of titanosaurs and related groups, including Diplodocoidea. Originally published in PLoS ONE 6(2):e16663 (2011).

Scale diagram showing the most complete members of Dicraeosauridae compared with a human silhouette, illustrating Amargasaurus's relative size among its relatives.

Published in Scientific Reports 9:1392, this paper described Bajadasaurus pronuspinax, a dicraeosaurid with anteriorly curved cervical spines. Phylogenetic analysis recovered Bajadasaurus as sister taxon to a clade including Amargasaurus, Brachytrachelopan, and Dicraeosaurus. The persistence of extremely long spines for 15 million years across dicraeosaurids led the authors to propose these structures functioned as passive defense against predators, providing crucial evolutionary context for interpreting Amargasaurus spines.

Artistic interpretation of two Amargasaurus cazaui in display behavior, by Fred Wierum (2022). The revised version shows a single sail rather than double, reflecting the most recent scientific consensus.

Scientific reconstruction of Amargasaurus cazaui by Nobu Tamura (2016), based on Gregory S. Paul's proportions. Shows the animal in complete lateral profile, with the characteristic double spines and comparatively short neck for a sauropod.

Published in Journal of Vertebrate Paleontology 34(4):870-882, this study applied CT scanning to Amargasaurus's neurocranium. The 3D reconstruction of the endocranium and inner ear showed that when the lateral semicircular canal is horizontal, the occipital condyle points postero-ventrally, indicating the head was held with the muzzle angled downward. This is consistent with mid-height vegetation browsing, with the habitual snout position at 80 cm above ground and a maximum reach of 2.7 m.

Digital reconstruction of Amargasaurus cazaui by Mario Lanzas (2021), showing the low feeding posture consistent with endocranium data published by Carabajal et al. (2014).

Skeletal mount of Amargasaurus cazaui at the National Museum in Prague, Czech Republic, showing the reconstructed head and neck posture. Photograph by Jan Helebrant (public domain).

Published in Cretaceous Research 128:104965, this study examined the bone microstructure of the Amargasaurus cazaui holotype. Histological analysis revealed the individual was a young adult, at least 10 years old. Cortical bone showed highly vascularized fibrolamellar tissue interrupted by cyclical growth marks (LAGs), indicating rapid growth with seasonality. Clear separation between ossified epiphyses and diaphyses confirmed the animal had not reached maximum adult size.

Skeletal cast of Amargasaurus cazaui at Melbourne Museum, Australia. Replica of holotype MACN-N 15, the subject of the histological studies by Windholz and Cerda (2021).

Photomicrograph of compact bone histology showing osteons, Haversian canals, and lamellae under optical microscopy. The paleohistology study of dicraeosaurids analyzes transverse cross-sections of long bones from Amargasaurus and Dicraeosaurus to determine growth rates and life history strategies of these sauropods.

Published in Journal of Anatomy 240(6):1005-1019, this study examined in detail the bone microstructure of Amargasaurus cervical and dorsal neural spines. Cortical bone consists of highly vascularized fibrolamellar bone with cyclical growth marks. The absence of evidence for a keratinous sheath, combined with oblique Sharpey's fibers indicating robust interspinous ligaments, strongly supports the hypothesis of a skin sail covering the structures. The Sharpey fibers suggest successive spines were connected by a ligament system.

Skeletal mount of Amargasaurus cazaui in Coquimbo, Chile (2022). The single skin sail connecting the spines, supported by histological data from Cerda et al. (2022), is represented in modern scientific mounts.

Rear view of the Amargasaurus cazaui skeletal mount, by Kumiko (2015). The posterior angle highlights the parallel position of the two rows of hemineural spines, whose histological structures were investigated by Cerda et al. (2022).

Published in Cretaceous Research 117:104629, this paper reported new dicraeosaurid materials from the La Amarga Formation, the same unit that produced Amargasaurus cazaui. Two associated anterior dorsal vertebrae (MOZ-Pv 6126-1 and MOZ-Pv 6126-2) do not belong to any described species, indicating greater dicraeosaurid diversity in the Neuquén Basin than previously recognized. Phylogenetic analysis reaffirmed Amargasaurus's relationships within Dicraeosauridae.

Skeletal mount of Amargasaurus cazaui, photographed by Aleposta (2009). The articulated arrangement of vertebrae with double neural spines illustrates the morphology studied in the new dicraeosaurid remains from the La Amarga Formation.

Skeletal mount of Amargasaurus cazaui at the Museo di Storia Naturale dell'Università di Pisa, Italy (2010). The La Amarga Formation dicraeosaurid material described by Windholz et al. (2021) is compared to holotype MACN-N 15.

Published in PeerJ 3:e857, this is one of the most comprehensive phylogenetic studies of diplodocoids. Amargasaurus cazaui (MACN-N 15) was included as a dicraeosaurid representative, with Dicraeosauridae as sister group to Diplodocidae. The analysis confirmed that Diplodocidae consistently forms a sister group with Dicraeosauridae, together forming Flagellicaudata. The paper also reinstated Brontosaurus as a valid genus, demonstrating the power of specimen-level analyses for resolving diplodocoid relationships.

Skeletal mount of Amargasaurus cazaui at Melbourne Museum (2008), low-angle lateral view. The neck silhouette with double spines shows the most striking autapomorphy of the species within Dicraeosauridae.

Dinosaur exhibition at the Museo di Storia Naturale dell'Università di Pisa, Italy, including Amargasaurus cazaui. The diversity of forms displayed illustrates the morphological variation among Cretaceous sauropods.

Published in Journal of Anatomy 248(2):284-306, this study reconstructed the craniocervical musculature of Amargasaurus using the EPB (extant phylogenetic bracket) approach, comparing with extant archosaur anatomy. Results indicate that muscle insertions on the occiput are consistent with a mid-height feeding strategy, confirming neuroanatomical data from Carabajal et al. (2014). The study provides the most complete muscular reconstruction available for any dicraeosaurid.

Dinosaur exhibition at the Museo di Storia Naturale dell'Università di Pisa, including Amargasaurus. The Italian museum context reflects the wide international distribution of Amargasaurus cazaui replicas.

Skeletal mount of Amargasaurus cazaui at the Museo Municipal de Estepona, Málaga, Spain. The display alongside Carnotaurus illustrates the South American Cretaceous fauna represented in European museums.

Published in Ameghiniana 34(1):3-32, this work conducted phylogenetic analysis of titanosaurs and related groups, using Amargasaurus cazaui as a representative dicraeosaurid and reference point for calibrating relationships of derived sauropods. The study contributed to understanding relationships between diplodocoids and titanosaurs, two of the main sauropod groups of the Cretaceous, and provided foundational context for interpreting Amargasaurus's phylogenetic position within Sauropoda.

Size comparison of the most complete members of the sauropod family Dicraeosauridae, including Amargasaurus cazaui. The phylogenetic analysis by Salgado & Bonaparte discusses titanosaurid evolutionary relationships and the placement of dicraeosaurids within Diplodocoidea.

Skeletal mount of Amargasaurus cazaui alongside Carnotaurus sastrei at the Museo di Storia Naturale dell'Università di Pisa, Italy. The juxtaposition of the two South American dinosaurs illustrates the diversity of forms in Cretaceous Patagonia.

Published in Cretaceous Research 93:33-48, this work described a new dicraeosaurid from the Neuquén Basin, older than Amargasaurus (Valanginian vs. Barremian-Aptian). Phylogenetic analysis repositioned relationships within Dicraeosauridae and provided evolutionary context for the origin of Amargasaurus's extremely long cervical spines. The study indicates that elongated neural spines evolved progressively within the clade, with Amargasaurus representing the point of maximum specialization.

Skeletal mount of Amargasaurus cazaui at Melbourne Museum (2005). The species represents the peak of neural spine specialization within Dicraeosauridae, the group that includes the new taxon described by Carballido et al. (2019).

Skeletal mount of Amargasaurus cazaui at the Museum of Victoria, Melbourne (2007). Comparison with older new dicraeosaurids, like that described by Carballido et al. (2019), reveals the evolutionary trajectory of neural spines in the clade.

Full-size T-rex animatronic from the Jurassic Park franchise, with the iconic red Jeep — Amaury Laporte · CC BY 2.0