Yixianopterus

Yixianopterus Temporal range: Early Cretaceous, 124.6 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Order:	†Pterosauria
Suborder:	†Pterodactyloidea
Clade:	†Istiodactyliformes
Genus:	†Yixianopterus Lü et al., 2006
Type species
†Yixianopterus jingangshanensis Lü et al., 2006

Yixianopterus is a pterodactyloid pterosaur genus from the Barremian-Aptian-age Lower Cretaceous Yixian Formation of Liaoning, China. It is known from a single specimen, holotype JZMP-V-12, housed at the Benxi Geological Museum. This specimen was modified before acquisition, with much of the skull being fabricated.^[1] The Jinggangshan bedding in which the specimen was found is basaltic with siliciclastic sediments.^[2] Many organisms associated with this layer of the Yixian Formation are aquatic, indicating a marine environment with much volcanic activity.

Lü et al. (2006) assigned Yixianopterus to the Lophocratian family Lonchodectidae based on dental characters, and ratio comparisons between wing phalanx I and II, metacarpal IV, and ulna. This specimen was classified it as the first Asian representative of Lonchodectidae.^[3] Martill (2011) considered it potentially related to his new taxon Unwindia,^[4] and Witton (2013) assigned it to the family Ornithocheiridae.^[5]

A reappraisal of the holotype specimen and phylogenetic analysis by Jiang et al. (2020) recovered Yixianopterus as a basal member of the clade Istiodactyliformes:

Holotype JZMP-V-12 was discovered within the Jinggangshan bedding, the uppermost layer of the Yixian Formation.^[2] Many Jehol Biota associated with the Jinggangshan bedding are fish, ephemerid, and plant fragments. The holotype found contained fragmented segments leading to its classification as a new genus and species of flying reptile from the Early Cretaceous. Preserved segments include the right forelimb, a foot, and teeth.^[1]

The recovered right forelimb segment contained two broad, thin plates each measuring 35 cm x 35 cm x 2 cm. The conditions under which the holotype was preserved crushed the ends of the right humerus, but what remains is 101.6 mm long.^[1] The deltopectoral crest of the upper humerus, extending a quarter of the length (25.38mm), characterized the specimen as belonging to Pteranodontoidea.

The foot of holotype JZMP-V-12 was found in a well-preserved condition. Metatarsal III is 28.19mm long while what was preserved of the tibia is 102.63 mm in length. Kellner et al. (2019) identified the ratio as less than 27.5%, a typical characteristic of the clade Ornithocheiroidea.^[1]

Lü et al. (2006) identified the ratios between wing phalanx I and II, wing phalanx I and metacarpal IV, and metacarpal IV and ulna, as being unique to Yixianopterus^[3].

Lü et al. (2006) noted that the teeth of the specimen were subequal with diastema increasing posteriorly.^[3] Kellner et al. (2019) identified the triangular and labiolingually compressed teeth as a characteristic of Pteranodontoidea. The front two incisors are particularly more slender and longer than the rest.^[1]

An outline of the head preserved within the sediment showed a dorsal inclination.^[1] This would indicate that the shape of the skull is rather narrow where the mouth opening is, with the majority of the skull surrounding the brain.