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. Sinosonasus exhibits a similar condition: the skull is like those of basal troodontids, and the pelvis and hindlimb are like those of derived troodontids. In a phylogenetic analysis, Xu and colleagues found Jianianhualong in a polytomy with Sinusonasus and several other intermediate troodontids. For their 2019 description of Hesperornithoides, Scott Hartman and colleagues added Jianianhualong to an expanded and updated version of the phylogenetic dataset that was used for the analysis of Xu and colleagues. They found it as a member of the Sinovenatorinae, a group that was named in 2017 by Caizhi Shen and colleagues in their description of Daliansaurus. However, Hartman and colleagues noted that a position similar to that found by Xu and colleagues was also plausible: forcing Jianianhualong to be closer to the more derived Troodontinae required a phylogenetic tree that was only one step longer, and thus marginally less likely according to the principle of maximum parsimony. The strict consensus phylogenetic tree recovered by Xu and colleagues is reproduced below at left. The partially expanded strict consensus tree recovered by Hartman and colleagues is reproduced below at right (note that Troodontinae includes Troodon, Saurornithoides, and Zanabazar). Topology A: Xu et al. (2017) Topology B: Hartman et al. (2019) Implications for troodontid evolution The conjunction of basal and derived features as distinct regions of the body in Jianianhualong and Sinosonasus represent a possible case of mosaic evolution, in which natural selection acts upon distinct "modules" of the body. 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. However, this hypothesis is weakened by the presence of characteristics in both troodontids that do not follow the pattern. 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. Similarly, digit II of the foot in Sinusonasus is not as specialized as those of derived troodontids, despite the hindlimb being overall derived. Conversely, the forelimb of Jianianhualong is short