Fossils unearthed on a remote Argentine ranch belong to a new genus and species of macronarian sauropod dinosaur, according to an international team of paleontologists led by the Ludwig-Maximilians-Universität München.
Reconstruction of Bicharracosaurus dionidei. Image credit: Felipe Cutro-Lev.
The newly-described sauropod species lived on the southern supercontinent Gondwana about 157 million years ago, during the Late Jurassic epoch.
Named Bicharracosaurus dionidei, the dinosaur stretched roughly 20 m (65 feet) in length.
“Sauropoda is one of the main dinosaur lineages that represents one of the most important groups of herbivorous vertebrates during the Mesozoic,” said lead author Alexandra Reutter, a doctoral student at the Ludwig-Maximilians-Universität München, and her colleagues.
“Sauropods first appeared in the latest Triassic and survived until the end of the Cretaceous.”
“The group was taxonomically diverse and included the largest terrestrial animals that ever lived.”
“Within Sauropoda, a number of early-branching clades that flourished during the Jurassic were largely replaced by the derived Neosauropoda towards the end of this period.”
“Neosauropoda split early in their evolution into two major clades, the Diplodocoidea and the Macronaria, but, although this principal subdivision of Neosauropoda has been generally accepted since it was first proposed in the 1990s, there is still considerable debate about the referral of many taxa, especially from the Jurassic, to either of these subclades, or to Neosauropoda in general.”
The fossilized bones of Bicharracosaurus dionidei — including part of the spine, ribs and hip — were brought to the attention of the paleontologists by the local farmer Dionide Mesa in March 2001.
The site is part of the Cañadón Calcáreo Formation, exposed in the central to northern parts of Chubut province of Argentina.
Scientists have long relied heavily on fossils from North America, Europe and other parts of the northern hemisphere to reconstruct the rise of the Neosauropoda.
The Cañadón Calcáreo Formation and Tanzania’s Tendaguru Formation are among the few Gondwanan deposits from that era to preserve multiple sauropod skeletons.
“For a long time, there was only a single significant site on the southern continents, in Tanzania,” said senior author Professor Oliver Rauhut, a paleontologist at the Bayerische Staatssammlung für Paläontologie und Geologie and the Ludwig-Maximilians-Universität München.
“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.”
The fossilized remains suggest Bicharracosaurus dionidei belonged to Macronaria, the group of massive herbivores that later produced giants such as Brachiosaurus.
But the new dinosaur’s anatomy also shares surprising similarities with Diplodocidae, a different branch of sauropods known for animals such as Diplodocus.
To determine where the animal fit on the dinosaur family tree, the researchers tested its relationships using two separate phylogenetic datasets.
Most analyses placed Bicharracosaurus dionidei within Macronaria, and several suggested affinities with Brachiosauridae, the lineage that includes Brachiosaurus itself and the African giant Giraffatitan.
“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,” Reutter said.
The team’s paper was published online in the journal PeerJ.
_____
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
