An international consortium of paleontologists, spearheaded by researchers at Ludwig-Maximilians-Universität München, has announced the discovery of fossils on a remote Argentine ranch representing a novel genus and species of macronarian sauropod dinosaur.
Reconstruction of Bicharracosaurus dionidei. Image credit: Felipe Cutro-Lev.
This recently identified sauropod species inhabited the southern supercontinent known as Gondwana approximately 157 million years ago, during the Late Jurassic geological period.
Designated Bicharracosaurus dionidei, this dinosaur is estimated to have measured around 20 meters (65 feet) in length.
“Sauropoda constitutes one of the principal dinosaur clades and represents a paramount group of herbivorous vertebrates throughout the Mesozoic Era,” stated lead author Alexandra Reutter, a doctoral candidate at Ludwig-Maximilians-Universität München, in conjunction with her colleagues.
“Sauropods first emerged in the latest Triassic period and persisted until the close of the Cretaceous.”
“This group exhibited considerable taxonomic diversity and encompassed the largest terrestrial creatures ever to have existed.”
“Within the Sauropoda, several nascent clades that thrived during the Jurassic were largely supplanted by the more derived Neosauropoda toward the conclusion of this epoch.”
“Neosauropoda bifurcated early in its evolutionary trajectory into two principal clades: the Diplodocoidea and the Macronaria. While this fundamental subdivision of Neosauropoda has been widely accepted since its initial proposal in the 1990s, considerable debate persists regarding the classification of numerous taxa, particularly those originating from the Jurassic, into either of these subclades, or into Neosauropoda more broadly.”
The fossilized skeletal remains of Bicharracosaurus dionidei, which include portions of the vertebral column, ribs, and pelvic girdle, were brought to the attention of the paleontological team by local rancher Dionide Mesa in March 2001.
The excavation site is situated within the Cañadón Calcáreo Formation, an exposed geological stratum found in the central to northern regions of Argentina’s Chubut province.
For a considerable duration, scientists have placed significant reliance on fossil evidence from North America, Europe, and other locales in the northern hemisphere to elucidate the ascendancy of the Neosauropoda.
The Cañadón Calcáreo Formation, alongside Tanzania’s Tendaguru Formation, ranks among the scarce Gondwanan geological deposits from that geological epoch that have yielded multiple sauropod skeletons.
“For an extended period, there was only a solitary significant fossil locality on the southern continents, specifically in Tanzania,” commented senior author Professor Oliver Rauhut, a paleontologist affiliated with the Bayerische Staatssammlung für Paläontologie und Geologie and Ludwig-Maximilians-Universität München.
“The fossiliferous site in Argentina’s Chubut province, from which Bicharracosaurus dionidei originates, furnishes invaluable comparative material. This enables us to continually augment and reassess our comprehension of the evolutionary trajectory of these animals, particularly within the southern hemisphere.”
The fossilized remnants indicate that Bicharracosaurus dionidei belonged to the Macronaria, a group of immense herbivorous dinosaurs that subsequently gave rise to colossal species such as Brachiosaurus.
However, the anatomical characteristics of this new dinosaur also exhibit notable congruencies with Diplodocidae, a distinct lineage of sauropods characterized by creatures like Diplodocus.
To ascertain the precise placement of this creature within the dinosaur family tree, the research team subjected its evolutionary relationships to scrutiny using two independent phylogenetic datasets.
The majority of analytical outcomes positioned Bicharracosaurus dionidei within the Macronaria, with several analyses suggesting affiliations with Brachiosauridae, the evolutionary line that includes Brachiosaurus itself and the African giant Giraffatitan.
“Our phylogenetic analyses of the preserved skeleton strongly suggest that Bicharracosaurus dionidei was closely related to the Brachiosauridae, which would signify its distinction as the inaugural Brachiosauridae discovered in South America from the Jurassic period,” remarked Reutter.
The research team’s findings have been formally documented in a published paper, which is now accessible online through the journal PeerJ.
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A. Reutter et al. 2026. Bicharracosaurus dionidei, gen. et sp. nov., a new macronarian (Dinosauria, Sauropoda) from the Late Jurassic Cañadón Calcáreo Formation of Argentina and the problematic early evolution of macronarians. PeerJ 14: e20945; doi: 10.7717/peerj.20945
