Butler, R.J., Barrett, P.M., and gower, D.J. (2009). "Postcranial skeletal pneumaticity and air-sacs in the earliest pterosaurs." Biology Letters, 5(4): 557-560. DOI:10.1098/rsbl.2009.0139
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Fucheng Zhang, Zhonghe Zhou, Xing Xu, Xiaolin Wang & Corwin Sullivan, "A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers", Nature 455, 1105-1108 (23 October 2008). The authors note that "The age of the Daohugou sediments is contentious, with possible dates ranging from Middle Jurassic to Early Cretaceous. However, published radioisotopic dating results span a narrower range from 152 to 168 Myr (Middle to Late Jurassic)"
