Niebla antiqua

Niebla antiqua is an extinct species of abelisaurid theropod dinosaurs from the Late Cretaceous (Campanian–Maastrichtian)^[1] of Río Negro province, Argentina. Niebla antiqua is the only species in the genus Niebla, known from a partial, non-articulated skeleton. The holotype, found in the Allen Formation, represents an adult individual about nine years old in minimum age.^[2][3]

Niebla antiqua Temporal range: Late Cretaceous, 79–69 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Speculative life restoration
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Family:	†Abelisauridae
Clade:	†Brachyrostra
Genus:	†Niebla Rolando et al., 2020
Species:	†N. antiqua
Binomial name
†Niebla antiqua Rolando et al., 2020

Discovery and naming

The holotype, MPCN-PV-796, was found near Matadero Hill, 70 kilometres (43 mi) south of General Roca, Río Negro Province, Argentina. The fossil material includes a near-complete braincase, fragmentary jaw and teeth, relatively complete scapulocoracoid, dorsal ribs and incomplete vertebrae.^[2]

The genus name Niebla comes from the Spanish word for "mist", referring to the foggy days during the excavation of the fossil. The specific name, antiqua, is derived from a Latin word meaning "old."^[2]

Description

Niebla represents one of the most derived abelisaurids. Despite its relatively small size, especially when compared to related dinosaurs like Carnotaurus, the holotype represents an adult. Based on the remains, Niebla would have been roughly 4–4.5 metres (13–15 ft) long.^[2]

The scapulocoracoid is notably similar to that of Carnotaurus in having a posterodorsally oriented glenoid, a dorsoventrally expanded and wide coraco-scapular plate, and a very narrow and straight scapular blade. These features are very different from those of other abelisaurids, which may indicate a unique conformation of the pectoral girdle among these South American theropods.^[2]

Paleoecology

Niebla and other dinosaur fauna from the Allen Formation (Niebla in yellow, second from left)

Niebla is known from the Allen Formation of Argentina. The pterosaur Aerotitan, as well as many theropods (Quilmesaurus, Bonapartenykus, Austroraptor), sauropods (Bonatitan, Aeolosaurus, Menucocelsior, Panamericansaurus, Pellegrinisaurus, Rocasaurus), the ankylosaur Patagopelta, and ornithopods (Lapampasaurus, Kelumapusaura, Willinakaqe, and Bonapartesaurus), are also known from the formation.^[4][5][6][7]