Strange 65-Foot Dinosaur Discovered in Argentina

Bicharracosaurus dionidei, a newly discovered sauropod from Argentina, shows a mix of brachiosaurid and diplodocid traits, offering new insights into dinosaur evolution in the Southern Hemisphere.

Long-necked dinosaurs, known as sauropods, are often what people picture when they think of dinosaurs. With their huge bodies, long necks and tails, and small heads, they include the largest land animals ever discovered. Some reached lengths of up to 40 meters (about 131 feet), with well-known examples such as Diplodocus and Brachiosaurus.

A newly identified species from southern Argentina, Bicharracosaurus dionidei, was smaller but still impressive. Researchers estimate it measured about 20 meters (around 66 feet) in length.

Scientists recovered parts of its spine, including more than 30 vertebrae from the neck, back, and tail, along with several ribs and part of the pelvis. The bone structure shows the remains belonged to an adult that lived on Gondwana about 155 million years ago.

The fossil stands out because it displays a combination of traits seen in different sauropod groups. Some bones resemble those of Giraffatitan, a brachiosaurid from Tanzania. Others, especially the dorsal vertebrae, are more similar to Diplodocus and related species from North America.

Evolutionary Insights and Southern Hemisphere Gaps

“Our phylogenetic analyses of the skeleton indicate that Bicharracosaurus dionidei was related to the Brachiosauridae, which would make it the first Brachiosauridae from the Jurassic of South America,” says LMU doctoral student Alexandra Reutter, the study’s first author. She examined the fossil as part of her doctoral research.

“Our knowledge of the evolution of sauropods from the Late Jurassic has so far been based almost entirely on numerous fossil findings from North America and other sites in the Northern Hemisphere. For a long time, there was only a single significant site on the southern continents, in Tanzania.”

“The fossil site in the Argentine province of Chubut, from which Bicharracosaurus dionidei originates, provides us with important comparative material, allowing us to continuously supplement and reevaluate our understanding of the evolutionary history of these animals, particularly in the Southern Hemisphere,” says leader of the study and dinosaur expert Prof. Oliver Rauhut of the Bavarian State Collections of Natural History (SNSB).

The first fossils of Bicharracosaurus dionidei were discovered by shepherd Dionide Mesa on his farm, and the species was named in his honor. The genus name comes from “bicharraco,” a colloquial Spanish term meaning “big animal.” The remains were discovered in the Cañadón Calcáreo formation in Chubut Province, Patagonia, and are now kept at the Museo Paleontológico Egidio Feruglio in Trelew, Argentina.

Reference: “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” by Alexandra Reutter, José Luis Carballido, Guillermo José Windholz, Diego Pol and Oliver W.M. Rauhut, 16 April 2026, PeerJ.
DOI: 10.7717/peerj.20945

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