Two later studies in 2007 and 2011 both showed that H. jii was in fact more closely related to Sinopterus than to the two other species also assigned to Huaxiapterus, "H." corollatus and "H." benxiensis.

[8] A 2021 study by Darren Naish and colleagues of variation within pterosaur growth stages noted that numerous species had been classified as Sinopterus or "Huaxiapterus", most based only on a single specimen, and most differentiated from each other by features like wing proportions, skull length, and crest shape and size.

They suggested that a larger study would be needed to untangle the question of how many species of Sinopterus-like pterosaurs actually existed in the Jiufotang ecosystem, and how they are related to each other.

[9] The cladogram below follows the 2014 analysis by Brian Andres and colleagues, showing the placement of two Sinopterus species ("S." gui and S. dongi) within the clade Tapejaromorpha.

Based on their reassessment of the Sinopterus species-complex, Pêgas et al. modified their working dataset, previously used in the redescription of Aerotitan.

[10] Their cladogram is shown below:[11]Thalassodromidae Caupedactylus ybaka Aymberedactylus cearensis Europejara olcadesorum Tupandactylus imperator Tupandactylus navigans Tapejara wellnhoferi Caiuajara dobruskii Huaxiadraco corollatus Eopteranodon lii Sinopterus dongi Wightia declivirostris Afrotapejara zouhrii Bakonydraco galaczi Sinopterus is known from several specimens at various stages of growth, which has allowed scientists to study the changes these animals went through during their life histories.

The type specimen of N. crypticus, catalog number IVPP V-14377, is housed in the collection of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, China.

It was discovered in the Luzhhouou locality of Yaolugou Town, Jianchang County, Huludao City, western Liaoning Province in northeastern China.

[12] Wang et al. (2008), who originally described the specimen, concluded that it was immature, citing the amount of bone fusion and the ossification of the toes, gastralia, and sternum as indicating that it was a sub-adult rather than a hatchling.

However, Darren Naish argued on his popular weblog that, due to the hypothesis that pterosaurs were highly precocial, bone fusion and ossification could have occurred very early in life, and that Nemicolopterus might in fact be a hatchling Sinopterus.