Aniksosaurus darwini gen. et sp. nov., a new coelurosaurian theropod from the Early Late Cretaceous of Central Patagonia, Argentina

Abstract

The theropod dinosaur Aniksosaurus darwini gen. et sp. nov. has been recovered from the Upper
Cretaceous, Bajo Barreal Formation, of Central Patagonia. Aniksosaurus darwini gen. et sp. nov. was a small
tetanurine, approximately 2 meters long. Aniksosaurus exhibits several unique traits (e.g., cranial cervical vertebrae
with dorsoventrally deep neural arches, provided with a pair of cavities at their cranial surfaces; neural
canal wide; cranial caudals with ventral sagittal keel, and transverse processes triangular-shaped in dorsal
view; manual ungual phalanges robust; ilium with extremely expanded brevis shelf; femur with deep notch for
M. Iliotrochantericus; metatarsal and digit IV of pes transversely narrow). Available postcranial bones of
Aniksosaurus exhibit derived features of Coelurosauria (e.g., ilium with well developed cuppedicus fossa; femur
with anterior trochanter proximally projected, almost reaching the level of the articular head; greater trochanter
craniocaudally expanded; femoral head rectangular-shaped in cranial aspect; and fibular shaft
craniocaudally narrow), as well as characteristics suggesting that the new Patagonian taxon is more derived
than some basal coelurosaurians such as compsognathids, Ornitholestes, and coelurids. Comparisons with
maniraptoriforms (a clade including Ornithomimosauria, Tyrannosauridae, Oviraptorosauria, Alvarezsauridae
and Paraves) support that Aniksosaurus is less derived than these theropods. In sum, Aniksosaurus is here
considered as a Late Cretaceous survivor of a basal coelurosaurian radiation.