Description and Classification

Bicentenaria was a relatively small, meat-eating dinosaur. It walked on two legs and had a slender build, typical of many coelurosaurs. Scientists estimate its total body length to be around 2.5 to 3 meters (approximately 8.2 to 9.8 feet) and it would have weighed significantly less than larger predators. The discovery of multiple individuals together provides valuable information, suggesting these animals might have died in the same location, though whether they lived in groups is not definitively known.

Bicentenaria belongs to the group Coelurosauria. This is a very diverse and important clade of theropod dinosaurs that includes famous members like Tyrannosaurus rex, velociraptors, ornithomimids (ostrich-like dinosaurs), and even modern birds. When first described, Bicentenaria was considered a basal (early-branching) coelurosaur. Its exact position within Coelurosauria is still a subject of study, with some analyses suggesting it might be related to compsognathids, another group of small, agile theropods, or perhaps to an early lineage of tyrannosauroids. Understanding its relationships helps scientists piece together the early evolution and spread of coelurosaurs, especially in the Southern Hemisphere.

Distinguishing Features

Bicentenaria helps paleontologists understand the diversity of smaller theropods. Some of its key features include:

• Relatively small size compared to many other theropods, particularly those from the Candeleros Formation like Giganotosaurus.
• A slender and lightly built skeleton, suggesting it was an agile and fast-moving hunter.
• The fossil remains include bones from both juvenile and adult individuals, which can help scientists study how Bicentenaria grew.
• It possesses a combination of primitive and more advanced anatomical traits typical of early coelurosaurs, making its classification interesting.
• Its teeth were small and sharp, suited for a diet of small animals.

Paleoenvironment and Diet

Bicentenaria lived in what is now Patagonia, Argentina, during the Late Cretaceous period. The Candeleros Formation, where its fossils were found, represents an ancient environment characterized by extensive river systems (fluvial environment) with floodplains, lakes, and forests of conifers. The climate was likely warm and relatively humid.

This ecosystem supported a rich variety of life. Alongside Bicentenaria, paleontologists have found fossils of giant sauropod dinosaurs like Argentinosaurus, large predatory theropods such as Giganotosaurus and Mapusaurus, as well as other dinosaurs, crocodiles, turtles, fish, and early mammals. As a small carnivore, Bicentenaria would have occupied a different ecological niche than these larger predators. It likely hunted small vertebrates such as lizards, early mammals, frogs, and perhaps the young of other dinosaurs. Its agility would have been an asset for chasing down prey and avoiding larger predators in its environment.

Significance and Ongoing Research

The discovery of Bicentenaria is significant because it adds to our knowledge of coelurosaurian dinosaurs from Gondwana, the ancient supercontinent that included South America. Many well-known coelurosaurs come from the Northern Hemisphere (Laurasia), so finds like Bicentenaria provide crucial information about the evolution and diversity of these dinosaurs in southern landmasses.

Its fossils help fill a gap in the record for small-bodied theropods from this particular time and place in South America. The presence of multiple individuals allows for studies on variation within the species and potentially social behavior, although more evidence is needed for firm conclusions about group living. Ongoing research may involve further detailed anatomical studies of the existing fossils to better understand its biology and its evolutionary relationships with other coelurosaurs like Compsognathus or early tyrannosauroids. Future fossil discoveries in the Candeleros Formation could also shed more light on Bicentenaria and the ecosystem it inhabited.