Sinopterus
Sinopterus (meaning "Chinese wing") was a genus of tapejarid pterodactyloid pterosaur from the Aptian-age Lower Cretaceous Jiufotang Formation of Chaoyang, Liaoning, China. It was first described and named by Wang Xiaolin and Zhou Zhonghe. Three species have been classified in this genus, though only two are generally considered to be valid. Sinopterus is known for its proportionally large skull, which has a birdlike pointed beak, a long bony crest that starts with a tall premaxillaand goes back along the middle of the skull to form a point overhanging the rear of the skull, and its lack of teeth.
The type species, S. dongi, is based on IVPP V13363, an articulated, nearly complete skeleton. The skull of this individual was 17 centimeters (6.7 inches) long, and the wingspan was estimated to be 1.2 meters (3.9 feet). The authors suggested that it was an omnivore, and noted that it was the first record of a tapejarid outside of Brazil, and the earliest and most complete tapejarid.[1]
Sinopterus is known from numerous specimens, some of which have been assigned to unique species and even different genera over the years. The type species, Sinopterus dongi, is known from one specimen described in 2003. A second specimen, BPV-077, was also described in 2003 by Li, Lü, and Zhang, who classified it in its own species, S. gui. It was said to differ from S. dongi mainly in its smaller size (only about half the size of S. dongi) and the presence of a notarium,[2] though this was later disproved.[3] Some later studies found S. gui to simply represent a younger specimen of S. dongi,[4] though one large analysis in 2014 found it to be a more primitive tapejarid.[5]
A third specimen was referred to Sinopterus in 2007, again classified as a new species, this time given the name S. jii. This species was first named by Lü & Yuan in 2005 as the type species of a new genus which they named Huaxiapterus. 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. Both groups of researchers concluded that Huaxiapterus jii should therefore be reclassified as Sinopterus jii, and that the other two species of "Huaxiapterus" require a new genus name.[3][4] However, a more complete phylogenetic analysis suggested that Sinopterus may actually be an intermediate step in the grade between H. jii and the other two Huaxiapterus species, making Sinopterus paraphyletic if H. jii is included.[5]
In 2016, another species, S. lingyuanensis, was named. It purportedly differed from the other species in the proportions of its nasoantorbital fenestra, its rostral index, the relative sizes of its femur and tibia, and the relative sizes of the first and second wing digits. In the same paper describing this species, the species Huaxiapterus atavismus was also named.[6] However, Xinjun Zhang and colleagues in 2019 considered Huaxiapterus an invalid genus and therefore reassigned H. atavismus to Sinopterus, which created the new combination Sinopterus atavismus.[7]
