A curiosity of evolution has just been unearthed in Argentina. A new long-necked dinosaur, named Bicharracosaurus dionidei, displays a surprising mix of features from two distinct groups of sauropods.
This specimen, which lived about 155 million years ago on the supercontinent Gondwana, measured about 66 feet (20 meters) long. Though smaller than some of its cousins, it has a unique spine. Paleontologists unearthed over thirty vertebrae, ribs, and part of the pelvis, enough to confirm it was a healthy adult.
Reconstruction of Bicharracosaurus dionidei. Credit: Felipe Cutro-Lev
Analysis of its bones revealed an unexpected combination. Some vertebrae resemble those of Giraffatitan, a brachiosaur from Africa, while others are more reminiscent of diplodocus from North America. This mix of traits had never been observed in a sauropod from the Southern Hemisphere for that time period.
According to researchers, Bicharracosaurus dionidei is the first Jurassic brachiosaurid discovered in South America. Until now, knowledge about the evolution of Late Jurassic sauropods came almost exclusively from fossils found in the Northern Hemisphere, mainly in North America and Tanzania.
The species name honors its discoverer, shepherd Dionide Mesa, who found the first bones on his farm in Patagonia. The genus name, Bicharracosaurus, comes from a familiar Spanish term meaning "big animal." The fossils are now housed at the Egidio Feruglio Paleontological Museum in Trelew, Argentina.
Bicharracosaurus vertebrae being prepared at the Egidio Feruglio Paleontological Museum. Credit: Amalia Villafañe
This discovery fills an important gap in understanding sauropod evolution in the Southern Hemisphere. It shows that the diversity of these animals was much greater than imagined, and that exchanges between different lineages likely occurred much earlier than previously thought.