Abstract
BackgroundCentral Patagonia, Argentina, preserves an abundant and rich fossil record. Among vertebrate fossils from the Upper Cretaceous Bajo Barreal Formation of Patagonia, five individuals of the small, non-avian theropod dinosaur Aniksosaurus darwini were recovered. Group behavior is an important aspect of dinosaur paleoecology, but it is not well-documented and is poorly understood among non-avian Theropoda.Methods/Principal FindingsThe taphonomic association of individuals from the Bajo Barreal Formation and aspects of their bone histology suggest gregarious behavior for Aniksosaurus, during at least a portion of the life history of this species. Histology indicates that the specimens were juvenile to sub-adult individuals. In addition, morphological differences between individuals, particularly proportions of the appendicular bones, are probably related to body-size dimorphism rather than ontogenetic stage.Conclusions/SignificanceGregarious behaviour may have conferred a selective advantage on Aniksosaurus individuals, contributing to their successful exploitation of the Cretaceous paleoenvironment preserved in the Bajo Barreal Formation. The monospecific assemblage of Aniksosaurus specimens constitutes only the second body fossil association of small, coelurosaurian theropods in South America and adds valuable information about the paleoecologies of non-avian theropod dinosaurs, particularly in the early Late Cretaceous of Patagonia.
Highlights
Dinosaur behavior is difficult to infer from the fossil record
Sedimentology/Paleoenvironment The lithology and structure of the Bajo Barreal Formation at the Aniksosaurus site, supports deposition by a unidirectional, low-energy, overbank fluvial deposit, a floodplain deposit produced by the lateral migrating fluvial channel
Paleoenvironmental studies in the Bajo Barreal Formation suggest that the sandstone deposits represent multi-episodic, cross-bedded fluvial channels [20]
Summary
The majority of behavioral studies are based on track sites and bone beds [1,2]. Complex social behaviors, such as gregariousness (herding, flocking, etc.) have frequently been inferred from these kinds of data, as well as from associations of bones of conspecific individuals. Among non-avian theropods, associations of multiple conspecific individuals are less common than in other groups of dinosaurs. Among vertebrate fossils from the Upper Cretaceous Bajo Barreal Formation of Patagonia, five individuals of the small, non-avian theropod dinosaur Aniksosaurus darwini were recovered. Group behavior is an important aspect of dinosaur paleoecology, but it is not welldocumented and is poorly understood among non-avian Theropoda
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