Bicharracosaurus dionidei, a 20-Meter Patagonian Sauropod, Could Be the First Late Jurassic Brachiosaurid From South America

Overview

A German-Argentine team has formally described Bicharracosaurus dionidei, a roughly 20-meter long-necked dinosaur from the Late Jurassic of Patagonia, in a paper published in the open-access journal PeerJ. The animal lived on the southern supercontinent Gondwana about 155 million years ago, according to the Bavarian State Collections of Natural History, the institution whose researchers led the study. The fossil mixes traits seen in two famous and otherwise distinct sauropod lineages — brachiosaurids and diplodocids — and, if its brachiosaurid affinities are confirmed, would be the first member of the family Brachiosauridae known from the Jurassic of South America.

What we know

The holotype was recovered from the Cañadón Calcáreo Formation in Chubut province, in central Patagonia, as reported by Sci.News. The fossilized bones — including part of the spine, ribs and hip — were brought to the attention of the paleontologists by local farmer Dionide Mesa in March 2001, the same article notes; the species name honors him, while the genus name derives from “bicharraco,” a colloquial Spanish term meaning “big animal,” according to ScienceDaily.

Material recovered includes more than 30 vertebrae from the neck, back, and tail, along with several ribs and part of the pelvis, according to Phys.org. The bone structure indicates the remains belong to an adult animal. The specimen is now housed at the Museo Paleontológico Egidio Feruglio in Trelew, Argentina, the SNSB press release adds.

The paper was led by Alexandra Reutter, a doctoral student at the Ludwig-Maximilians-Universität München, with senior author Oliver Rauhut of the SNSB, Sci.News reports. The Argentine side of the team came from the country’s CONICET national scientific research council, the Buenos Aires Times notes.

The authors stop short of an unconditional family assignment. “Most analyses placed Bicharracosaurus dionidei within Macronaria, and several suggested affinities with Brachiosauridae,” Sci.News quotes the paper. Reutter framed the implication this way in a statement reproduced by ScienceDaily: “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.”

Why the mix of traits matters

Some of Bicharracosaurus’s skeletal parts resemble those of the African brachiosaurid Giraffatitan, while features of its dorsal vertebrae are reminiscent of Diplodocus and its close relatives from North America, the SNSB press release reports. The Everything Dinosaur blog, summarizing the paper, notes that “the dorsal vertebrae are similar to the dorsal vertebrae of diplodocids” while “some fossil bones are reminiscent of the bones of brachiosaurids,” as detailed in its writeup.

That combination is interesting because long-necked dinosaur fossils from the Jurassic of the Southern Hemisphere are rare. Less is known about sauropod evolution and radiation south of the equator than in the better-sampled north, the same blog observes. Rauhut, the senior author, said the new specimen “provides us with important comparative material, allowing us to continuously supplement and reevaluate our understanding of the evolutionary history of these animals,” in remarks reproduced by ScienceDaily.

What we don’t know

The authors themselves flag uncertainty about Bicharracosaurus’s precise place on the sauropod family tree: the Everything Dinosaur summary notes that “Bicharracosaurus sits in a somewhat uncertain evolutionary position,” and that the “first Brachiosauridae from the Jurassic of South America” framing applies only “if brachiosaurid affinity is confirmed,” per its writeup. The recovered material is also partial — vertebrae, ribs, and a fragment of the pelvis, with no skull described in the news coverage — leaving open questions about feeding ecology and body proportions that a more complete skeleton would address.

Reporting on the exact age differs slightly across outlets: Sci.News cites “about 157 million years ago,” while the SNSB release and most other outlets cite 155 million years; the Buenos Aires Times describes the period more loosely as “over 150 million years ago.” All sources place the animal in the Late Jurassic.