[D] Aniksosaurus darwini [sG] [T]
Martinez and Novas 2006
Saurischia Theropoda Tetanurae Coelurosauria
Bajo Barreal Formation, Central Patagonia, Argentina
Etymology: From Greek aniksi, spring, referring to September 21st (i.e., the beginning of the spring in the Southern Hemisphere), the day when the theropod was found; and Greek saurus, lizard. In honor of the great naturalist Charles Darwin, who visited Patagonia in 1832- 1833, inspiring him to reach clearer interpretations of the evolution of life that changed human thought forever.
Holotype: MDT-PV 1/48. Articulated right hindlimb including femur, fibula, tibia and foot
Small theropod with the following autapomorphies: cervical vertebrae with the neural arch pedicels unusually deep (i.e., 2.5 times the height of the centrum); wide neural canal on cervical vertebrae; cranial caudals with ventral saggital keel; manual ungual phalanges robust; iliac brevis shelf lateroventrally expanded; caudolateral surface of proximal femur with strong depression and rugosities presumably for the attachment for M. ischiotrochantericus; metatarsal IV and its correspondent digit transversely narrow.
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 considered as a Late Cretaceous survivor of a basal coelurosaurian radiation by the authors.