Құрып кеткен бауырымен жүретін динозавр - Аниксозавр

Extinct species of reptile

Aniksosaurus (meaning "spring lizard", from Modern Greek Άνοιξη, "Spring", referring to the fact it was found on 21 September 1995, the onset of Spring on the Southern Hemisphere) is a genus of avetheropod dinosaur from what is now Chubut Province, Argentina. It lived during the Cenomanian to Turonian of the Cretaceous period, between 96 91 million years ago. The type species, Aniksosaurus darwini, was formally described from the Bajo Barreal Formation of the Golfo San Jorge Basin by Rubén Dario Martínez and Fernando Emilio Novas in 2006; the name was first coined in 1995 and reported in the literature in 1997. The specific epithet honors Charles Darwin who visited Patagonia in 1832/1833 during the Voyage of the Beagle.

The type specimen MDT PV 1/48, discovered in the Bajo Barreal Formation, consists of an articulated right hindlimb, which includes the femur, fibula, tibia and foot. The longest femur discovered for this genus measures 247mm, and the longest tibia, 270mm. On average, the tibia is 13% longer than the femur in Aniksosaurus, an adaptation which has been strongly correlated with the development of cursorial habits in dinosaurs. Martinez and Novas (2006), based on femoral measurements, originally suggested that Aniksosaurus darwini was approximately long and tall at the hip, and weighed up to while Hartman et al. (2019) find it to be a maniraptoromorph outside compsognathids and maniraptorans, and Naish et al. (2022) find it to be a megaraptoran.

A diagnosis is a statement of the anatomical features of an organism (or group) that collectively distinguish it from all other organisms. Some, but not all, of the features in a diagnosis are also autapomorphies. An autapomorphy is a distinctive anatomical feature that is unique to a given organism. According to Martínez and Novas (2006), Aniksosaurus can be distinguished based on the following characteristics: The hypothesis suggesting gregarious (social) behavior is supported by the taphonomic association of individuals from the Bajo Barreal Formation and evidence garnered from analysis of its bone histology. The authors of this study, Ibiricu, Martínez, Casal and Cerda (2013) noted that this particular assemblage is only the second known body fossil association of small, coelurosaurian theropods discovered in South America. Syntarsus rhodiensensis, Albertosaurus sarcophagus and Sinornithomimus dongi. Aniksosaurus is likely to have exhibited gregariousness only during a specific interval of its life, most likely when it was a sub adult.

The remains of the type specimen MDT PV 1/48 were discovered in the Laguna Palacios Ranch locality in the lower Bajo Barreal Formation of Patagonia in Chubut, Argentina. The specimen was collected by Martínez in 1995 in green sandstone that was deposited between the Cenomanian stage and the Turonian stage of the Cretaceous period, between 96 91 million years ago, as shown by radiometric Ar Ar dating. This specimen is housed in the collection of the Museo Regional Desiderio Torres in Sarmiento, Chubut, Argentina. Remains of at least four more individuals, in 2006 assigned as the paratypes, were uncovered at the site.

Dinosaur remains from this formation include those of the abelisaurid theropod Xenotarsosaurus bonapartei, the sauropods Drusilasaura, Epachthosaurus and Campylodoniscus, the hadrosaur Secernosaurus as well as indeterminate teeth belonging to carcharodontosaurids and dromaeosaurids.

The nature of the lithology at the Aniksosaurus site suggests that the deposits were made by a low energy, unidirectional, overbank fluvial floodplain deposit, which was produced by a lateral migrating fluvial channel. The observation that sandstone tabular bodies were deposited with coarse sandstones and tuff interclasts also supports that Aniksosaurus was preserved in a fluvial environment. The soft tissue underwent subaerial weathering and then began to decompose, from the contributory action of small vertebrae scavengers as evidenced by a series of small grooves in one of the femora recovered, which was then followed by the partial disarticulation of the skeleton. Disarticulation was followed by reorientation of the remains by fluvial currents, which was then followed by differential burial in what appears to have been at least two stages of sedimentation. No evidence was found to support either cannibalism or intra specific competition.