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[dinosaur] Four-winged dinosaurs are cases of sexual dimorphism?

Ben Creisler

Checking other issues of the Journal of Geology, I found a paper from earlier this year that has not been mentioned. For now, there does not appear to be an open access link that works. I got an error message when the tried a couple of other journal sites that post Journal of Geology papers in open access. Same problem with the two more recent papers from the Journal of Geology.

WANG Xuri; JI Yannan; KUROSU Mariko;  JI Qiang (2016)
Four-winged dinosaurs or sexual dimorphism of dinosaurs.
Journal of Geology 40(1): 1-6

In recent years, several theropod dinosaurs with pennaceous feathers attached to the metatarsus have been reported from Western Liaoning, China. The findings are considered as new evidence to support the "tetrapteryx" hypothesis. By examining hundreds of specimens of Microraptor zhaoianus, ″M. gui″, Anchiornis huxleyi and Confuciusornis sanctus, and with mathematical statistics, we find that: ( 1) ″M. gui″ is synonymous with M. zhaoianus, and M. zhaoianus is a valid name. ( 2) Only some studied specimens show clear pennaceous feathers attached to the metatarsus or tarsometatarsus. ( 3) It is surely considered as sexual dimorphism, not the so-called four-winged dinosaurs. ( 4) These species have a distant relationship with birds, and they may be evolutionarily extinct collateral branches. ( 5) During the evolution from dinosaurs to birds, there should be a "gliding" stage,  rather than a "four-winged dinosaur" stage.