Jianianhualong (meaning "Jianianhua dragon") is a genus of troodontid theropod dinosaur from the Early Cretaceous of China. It contains a single species, Jianianhualong tengi, named in 2017 by Xu Xing and colleagues based on an articulated skeleton preserving feathers. The feathers at the middle of the tail of Jianianhualong are asymmetric, being the first record of asymmetrical feathers among the troodontids. Despite aerodynamic differences from the flight feathers of modern birds, the feathers in the tail vane of Jianianhualong could have functioned in drag reduction whilst the animal was moving. The discovery of Jianianhualong supports the notion that asymmetrical feathers appeared early in the evolutionary history of the Paraves.
Jianianhualong possesses a combination of traits seen in basal as well as traits seen in derived troodontids. This is consistent with its phylogenetically intermediate position among the troodontids. This mixture of traits shows a distinct spatial organization, with basal traits being present in the forelimbs and pelvis, and derived traits being present in the skull and hindlimbs. This may represent a case of mosaic evolution, where natural selection acts upon the form of the body in a modular way. Similar transitional patterns of traits are seen in the troodontid Sinusonasus, a close relative of Jianianhualong. Ecologically speaking, Jianianhualong and Sinusonasus are part of the considerable diversity of troodontids that is present within the Yixian Formation.
Jianianhualong is known from the type and only specimen, a nearly complete skeleton preserving feathers that is missing only the end of the tail. It is articulated and compressed on a stone plate. This holotype specimen is stored under the collection number DLXH 1218 in the Dalian Xinghai Museum, Liaoning Province, China. It was excavated using mechanical tools (geologist's hammers and chisels) from Early Cretaceous[1] rocks of the Yixian Formation in the locality of Baicai Gou (Chinese: 白菜溝), located in the Yixian County of Liaoning.[2] The Dakangpu Bed (equivalent to the Dawangzhangzi, Daxinfangzi, Hejiaxin, Sichakou, and Senjiru Beds),[3] which Baicai Gou is a part of,[4] is situated in the middle of the formation. The specific portion of the Beds from which Jianianhualong originates was dated in 2006 and 2008 to approximately 124.4 million years ago, which corresponds to the early Aptian.[5][6][7]
In 2017, Jianianhualong was named and described by a team of researchers including Xu Xing, Philip J. Currie, Michael Pittman, Xing Lida, Meng Qingjin, Lü Junchang, Hu Dongyu, and Yu Congyu, in a research paper published in Nature Communications. In order to investigate the preserved plumage of the specimen, Xu and colleagues made use of laser-stimulated fluorescence using a 405 nm laser.[8] The genus name combines the name of a company that sponsored the research of this taxon, Jianianhua (Chinese: 嘉年華), and the suffix long (Chinese: 龍), meaning "dragon". The specific name, tengi, honours Ms. Teng Fangfang who acquired the specimen and made it available for study.[2]
The type specimen of Jianianhualong measures approximately 1 metre (3 ft 3 in) as preserved; since the back of the tail is missing, the animal would probably have been around 1.12 metres (3 ft 8 in) long in life. Scaling from a femoral length of 11.7 cm (4.6 in), Xu et al. found that it weighed 2.4 kilograms (5.3 lb).[2][9] Despite its small size, the specimen was mature, as indicated by the fusion of the sutures in the vertebrae.[2][10][11]