Bicharracosaurus

MEANING: Big animal lizard

PERIOD: Late Jurassic

CONTINENT: South America

Bicharracosaurus is a large macronarian sauropod, possibly a brachiosaurid. Like all sauropods, this dinosaur walked on four pillar-like legs and used its long neck to reach vegetation which it processed in its large gut. Bicharracosaurus is estimated at approximately 15 m in total body length, and weighed around 20 t.

Abstract from paper: Our understanding of Late Jurassic sauropod faunas heavily relies on the fossil record of the northern hemisphere. During the last two decades, paleontological fieldwork in the Oxfordian-Kimmeridgian Cañadón Calcáreo Formation of Argentina has yielded several sauropod remains. Here we present a new taxon, Bicharracosaurus dionidei gen. et sp. nov., represented by a partial vertebral column and a fragment of the ilium. Anatomical as well as histological evidence suggest that the new specimen represents an adult individual. The posterior dorsals of Bicharracosaurus show great similarity with isolated mid- to posterior dorsal vertebrae previously referred to a diplodocid (MPEF-PV 1324) from the same formation. Some characters that supported a diplodocid position of the isolated vertebrae (pleurocoels with anteroventral fossa, dorsal margin of the pleurocoel angular and at the level of the neural canal) are also present in Bicharracosaurus. The phylogenetic position of Bicharracosaurus was tested using two recent datasets that include a large sample of basal eusauropods and basal neosauropods. The overall evidence supports a position of Bicharracosaurus within Macronaria with several analyses and diagnostic characters suggesting brachiosaurid affinities. Given the incomplete nature of the isolated vertebrae MPEF-PV 1324, their position is unstable across several analyses, but they show close affinities with either Bicharracosaurus or Diplodocidae. Despite the similarities between Bicharracosaurus and Tehuelchesaurus benitezii, a macronarian from the same formation, only in some of the phylogenetic results these two species were recovered as closely related, whereas in most analyses, Tehuelchesaurus formed a clade with Janenschia robusta as basal macronarians or non-neosauropod eusauropods. In addition, several diagnostic characters of Bicharracosaurus are absent in Tehuelchesaurus and vice versa. Our results also show that other putative macronarian taxa have incongruent positions depending on the dataset, even when controlling for taxonomic scope hindering our understanding of the early evolution of the clade.

Bicharracosaurus is from the Late Jurassic. The Late Jurassic was a dynamic period, spanning from about 162 to 143 million years ago. The continents were continuing to drift apart, and the supercontinent Pangaea had fully split into Laurasia in the north and Gondwana in the south. This continental rearrangement led to the formation of large inland seas and shallow coastlines that fostered diverse ecosystems. The climate during the Late Jurassic was warm and humid, with lush forests of conifers and ferns that stretched across much of the continents, creating a rich ecosystem where dinosaurs flourished the dominant land animals.

Dinosaurs continued to diversify through the Late Jurassic, with some of the most famous species evolving in this time. Many well-known sauropods, such as Brachiosaurus and Apatosaurus roamed the land, exhibiting niche partitioning with their selectively distinct neck positions. Alongside them, stegosaurs became widespread, their plates and spikes making them one of the era's most recognizable groups. Theropods like Allosaurus and Ceratosaurus were the apex predators, evolving large, powerful bodies and sharp teeth that allowed them to hunt the gigantic herbivores. The early evolution of birds was taking place, setting the stage for the numerous species that would fill the skies in the eras to come.

Unlike the dramatic mass extinctions that marked the beginning and end of the Mesozoic, the Jurassic Period ended without a sharp boundary. As the continents continued to drift, ecosystems gradually transformed into unique habitats that supported the more specialized dinosaur species of the Cretaceous.

Bicharracosaurus is a macronarian. Macronaria is a major clade of sauropod dinosaurs, characterized by their large nasal openings. This group includes some of the most famous and massive dinosaurs in history, such as Brachiosaurus and Camarasaurus, as well as their many relatives that flourished from the Jurassic through the Cretaceous Periods. Macronarians were herbivorous, long-necked dinosaurs with relatively upright neck posture, allowing them to feed from tall trees and vegetation other sauropods may not have reached. Their skulls tend to be short and boxy compared to the more elongated skulls of diplodocoids, and their teeth were often spoon-shaped, well-suited for stripping leaves rather than raking or cropping.

Early macronarians appeared in the Late Jurassic and were among the most common sauropods in their ecosystems. Later forms diversified dramatically, including the enormous titanosaurs that would dominate sauropod diversity in the Cretaceous. While the more basal members retained relatively conservative body plans, some later macronarians reached extreme sizes and adapted to a wide range of habitats. The group’s evolutionary success is reflected in its global distribution, with fossils found on every continent, including Antarctica. As some of the tallest terrestrial animals known from the fossil record, macronarians represent an important stage in the evolution of sauropod body plans and feeding strategies.