Author(s): Qiang Ji (corresponding author) [1, 2]; Shu-An Ji [2]; Yen-Nien Cheng [3]; Hai-Lu You [2]; Jun-Chang Lü [2]; Yong-Qing Liu [2]; Chong-Xi Yuan [4]

The recent discovery of a pterosaur egg with embryonic skeleton and soft tissues from the Yixian Formation confirmed that the flying pterosaurs were oviparous [1]. Here we describe another pterosaur egg whose exquisite preservation indicates that the shell structure was soft and leathery.

The new pterosaur egg with its embryo (JZMP-03-03-2; Fig. 1 and supplementary information) was collected from the Jingangshan Beds of the Yixian Formation in the Jingangshan area of Liaoning, China. Both this and the earlier pterosaur egg (IVPP V13758) are from beds of Early Cretaceous age, estimated to be 121 million years old by ⁴⁰ Ar/³⁹ Ar dating [2].

The presence of the pteroid bone and the long wing-phalanges and wing-metacarpals within the egg shows that JZMP-03-03-2 is an embryonic pterosaur [3, 4] (for composite drawing, see supplementary information). The ilium and tibia are completely preserved, but the pubis, pteroid and dorsal vertebrae are only partially ossified. The pteroid has a slightly bent proximal end. The forelimb bones have embryonic characteristics, such as longitudinal shallow grooves on the shaft. The humerus is robust and complete, with a length of 17 mm; the deltopectoral crest is only weakly ossified. The radius and ulna (about 26 mm long) are straight and much longer...