The tapejarid pterosaurs flourished in the Jehol Biota with an abundance of immature individuals and a rarity of individuals at skeletal maturity. Most of these individuals plot well on an ontogenetic series based on the proportions of limb elements, but this has lacked histological evidence until now. Here, a new wing skeleton of Sinopterus was thin-sectioned to provide the first histological data about the ontogeny of the Jehol tapejarids. Histologically, the new specimen is an immature individual at a late juvenile stage prior to sexual maturity. It is grouped with medium-sized and medium-crested individuals, which are distinct from the small-sized and crestless individuals as well as the rare large-sized and large-crested individuals at skeletal maturity, supporting the presence of the premaxillary crest as an ontogenetic feature in the Jehol tapejarids. Furthermore, this histology indicates that the largest skeletally immature individuals might have reached the sexual maturity. Enigmatically, there is a size gap between sexual and skeletal maturity, which is at about 79% of the large size, implying a ontogenetic strategy comparable with Pteranodon and possibly with the Brazilian tapejarid Caiuajara. This size gap is consistent with lack of the larger sexually mature individuals in the Jehol Biota, which is hypothesized to be a migratory habitat for the Jehol tapejarids.
Abstract. In the Jehol Biota, the filter-feeding ctenochasmatid pterosaurs flourished
with a high biodiversity. Here, we report a new wing skeleton of the
ctenochasmatid Forfexopterus from the Early Cretaceous Jiufotang Formation in Jianchang,
western Liaoning, China. The specimen exhibits the sole autapomorphy, the
first wing phalanx shorter than the second and longer than the third.
Interestingly, it exhibits a skeletal maturity with co-ossified elements, but it
is only about 75 % the size of the immature holotype. This discrepancy
reveals developmental variation of Forfexopterus, but its relationship with sexual
dimorphism needs to be certain by more available material.
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