Niebla antiqua

Niebla antiqua was a species of abelisaurid theropod dinosaur that lived during the Late Cretaceous (Maastrichtian) in what is now Río Negro Province, Argentina. It is the sole species within the genus Niebla, and is known only from a partial, non-articulated skeleton. The holotype specimen, discovered in the Allen Formation, belonged to an adult individual that was at least nine years old at the time of death.

The holotype, catalogued as MPCN-PV-796, was unearthed near Matadero Hill, about 70 kilometers south of General Roca in Río Negro Province. The recovered bones include a nearly complete braincase, fragmentary jaw pieces and teeth, a relatively complete scapulocoracoid, dorsal ribs, and several incomplete vertebrae. The genus name *Niebla* is the Spanish word for "mist," chosen because of the foggy conditions during the fossil’s excavation. The species name *antiqua* comes from Latin, meaning "old."

In terms of anatomy, Niebla is considered one of the most derived abelisaurids. Although it was relatively small—estimated at 4 to 4.5 meters (13–15 feet) in length—the holotype was a fully grown adult, especially when compared to larger relatives like *Carnotaurus*. Its scapulocoracoid closely resembles that of *Carnotaurus* in several features: a posterodorsally oriented glenoid, a dorsoventrally expanded and wide coraco-scapular plate, and a very narrow, straight scapular blade. These traits differ markedly from those of other abelisaurids, suggesting a unique arrangement of the pectoral girdle among South American theropods.

Niebla is known exclusively from the Allen Formation in Argentina. This formation also preserves the pterosaur *Aerotitan*, as well as numerous other dinosaurs: the theropods *Quilmesaurus*, *Bonapartenykus*, and *Austroraptor*; the sauropods *Bonatitan*, *Aeolosaurus*, *Menucocelsior*, *Panamericansaurus*, *Pellegrinisaurus*, and *Rocasaurus*; the ankylosaur *Patagopelta*; and the ornithopods *Lapampasaurus*, *Kelumapusaura*, *Willinakaqe*, and *Bonapartesaurus*.