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 discovery of Jianianhualong supports the notion that asymmetrical feathers appeared early in the evolutionary history of the Paraves.

Ecologically speaking, Jianianhualong and Sinusonasus are part of the considerable diversity of troodontids that is present within the Yixian Formation.

This holotype specimen is stored under the collection number DLXH 1218 in the Dalian Xinghai Museum, Liaoning Province, China.

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.

In order to investigate the preserved plumage of the specimen, Xu and colleagues made use of laser-stimulated fluorescence using a 405 nm laser.

The inner surface of the frontal suggests details about the braincase, including the widened olfactory tract and back of the cerebrum.

Also uniquely, the front rim of the neural spine is thickened, while the rear portion is strongly expanded at the top.

[2] The bottom of the large, four-sided coracoid extends backwards with a hook-like projection, the postglenoid process, which is similar in length to that of Sinornithoides but longer than that of Sinovenator.

The first phalanx of the first digit is unusually long; it bears a "heel" at its top end, as well as a large groove on the interior surface that extends for more than half the bone's length.

Below the ilium, the left and right pubes are conjoined into the unusually broad "pubic apron" that is characteristic of troodontids, with a ridge on the rear surface as in Sinovenator.

Further below, like derived troodontids and dromaeosaurids, the "sickle claw" of the second digit is strongly curved and bears a prominent flexor tubercle (the portion which articulates with the phalanx).

[2] Like Jinfengopteryx, Anchiornis, and Archaeopteryx, the tail of Jianianhualong supports a frond-like fan of pennaceous feathers along its entire length.

The forelimbs and pelvis largely resemble basal troodontids such as Sinovenator: the short deltopectoral crest on the humerus; the long hand, metacarpal II, and phalanx III-2 on the hand; the small ilium; the ridge on the pubic apron; and the short ischium with two projections and an obturator process near the bottom of the bone.

[16][15] At the same time, the skull and hindlimbs resemble derived troodontids: the deep jugal branch of the maxilla bearing a prominent groove, the sub-triangular antorbital fossa; the relatively long maxillary fenestra; the short jugal branch of the postorbital bone; the long hallux; the slender and short metatarsal II; the "heel" on phalanx II-2; and the large, curved sickle claw.

The partially expanded strict consensus tree recovered by Hartman and colleagues is reproduced below at right (note that Troodontinae includes Troodon, Saurornithoides, and Zanabazar).

Scansoriopterygidae) Archaeopterygidae Halszkaraptorinae Unenlagiinae Dromaeosauridae Mei long Xiaotingia zhengi Sinovenator changii Jianianhualong tengi Almas ukhaa Liaoningvenator curriei Daliansaurus liaoningensis Hesperornithoides miessleri Sinusonasus magnodens Byronosaurus jaffei Sinornithoides youngi Gobivenator mongoliensis Geminiraptor suarezarum Urbacodon itemirensis Troodontinae The conjunction of basal and derived features as distinct regions of the body in Jianianhualong and Sinusonasus represent a possible case of mosaic evolution, in which natural selection acts upon distinct "modules" of the body.

[18] Indeed, the pattern in which basal and derived features are present seems to follow the domains of the body that are regulated by Hox genes, which have previously been discussed in the context of pterosaurs such as Darwinopterus.

In Jianianhualong, for instance, the large antorbital fenestra, long tooth row of the maxilla, and finely-serrated teeth represent basal characteristics in an otherwise derived skull.

[33][34] However, these feathers differ from those of modern birds in that the barbs of the trailing edge also have a relatively low angle of approximately 15°.

The hadrosauroid Jinzhousaurus is known from Baicai Gou, the same locality as that of Jianianhualong, as is the maniraptoran Yixianosaurus as well as hundreds of specimens from the choristodere Hyphalosaurus.

From elsewhere in the Dakangpu/Dawangzhangzi Beds, specimens have been discovered belonging to the birds Confuciusornis, Hongshanornis, Grabauornis, Liaoxiornis, Longicrusavis, Shanweiniao, Shenqiornis, and Zhongornis; the non-avialan theropod Sinosauropteryx; the ceratopsian Psittacosaurus; the pterosaur Cathayopterus; the lizards Dalinghosaurus and Yabeinosaurus; the choristoderes Hyphalosaurus and Monjurosuchus, of which the former is highly abundant; the turtle Manchurochelys; the mammals Acristatherium, Akidolestes, Chaoyangodens, Eomaia, Sinobaatar, and Sinodelphys; the frog Liaobatrachus; and fish, including Lycoptera (of which L. davidi is numerous), Peipiaosteus, and Protopsephurus.

Environmentally, Jianianhualong lived in a lacustrine area, as evinced by the tuffaceous sandstone present throughout the Dawangzhangzi Beds.

Like the rest of the Yixian Formation, the environment represented by these assemblages was seasonally semi-arid, with a low mean air temperature of 10 ± 4 °C (50 ± 7 °F).

The local flora consists of a mixed assemblage of gymnosperms, such as Czekanowskia, Schizolepis, and the ephedroids Amphiephedra, Chengia, Ephedrites, and Liaoxia; and also early angiosperms, including Archaefructus, Hyrcantha (formerly Sinocarpus), Leefructus, and Potamogeton.