Daanosaurus (meaning "Da'an lizard" after Da'an district in Zigong, Sichuan) was a genus of dinosaur. It was a sauropod which lived during the Late Jurassic (Oxfordian - Tithonian stage, about 163 - 145 mya). It lived in what is now China (Sichuan Province), and was similar to Bellusaurus.[1]
The type species from the Upper Shaximiao Formation was described in 2005 as Daanosaurus zhangi.[2] Adult size is unknown due to a lack of fossil remains. The holotype (ZDM 0193), which is the only known specimen, was a juvenile.
When it was described, Daanosaurus was placed in the Bellusaurinae, a sub-family of Brachiosauridae that Dong Zhiming had raised in 1990 to house Bellusaurus, or the Klamelisauridae (also now merged with Brachiosauridae), used to house Klamelisaurus and possibly also Daanosaurus and Abrosaurus. However, this classification is primarily based on the similarity in size with Bellusaurus. Furthermore, in its original description, Daanosaurus was found not to display any characteristics of the Brachiosauridae.[3] More recently, Daanosaurus was placed in the Macronaria due to its opisthocoelous posterior dorsal vertebrae,[4] but this trait is also present in mamenchisaurids.[5]
In 2023, the mamenchisaurid Mamenchisaurus sinocanadorum was redescribed and the phylogenetic analysis performed in the study included Daanosaurus, based on personal observations of the material by one of the authors. When characters that vary through growth were included in the dataset, both Daanosaurus and Bellusaurus were recovered as mamenchisaurids. The authors found that the characters that supported this hypothesis were only found in mamenchisaurids. The results of the analysis are shown below:[6]
The authors of the study also acknowledged the possibility that Daanosaurus and Bellusaurus may be members of an early-branching group of the Diplodocoidea that shared unique features with mamenchisaurids. Their status as juveniles, the authors noted, was probably the reason to the uncertainty in their phylogenetic position.