…or two bits of good news for us. This week's Nature has back-to-back articles on the discovery of two new fossilized pterosaur embryos, one in China and the other in Argentina.

The Chinese fossil hasn't been assigned to a specific species, but the authors compare it to another pteradactyloid, Beipiaopterus. It's from the early Cretaceous, about 120 million years ago, and its parents were living along the shores of a shallow freshwater lake. There is sufficient detail to be able to tell that it's shell was thin and leathery, and not calcareous like a chicken egg.

Early Cretaceous pterosaur egg and embryo (JZMP-03-03-2) from the Yixian Formation of Liaoning, China. Scale bar, 1 cm. Inset, magnification of egg boundary (130%) showing the thin, soft shell and no evidence of lamination structures.

Drawing of the pterosaur egg with embryo. Abbreviations: dv, dorsal vertebrae; fe, femur; hu, humerus; il, ilium; pt, pteroid; pu, pubic; ra, radius; sk, skull outline; t, tooth; ti, tibia; ul, ulna; wm, wing metacarpal; wp, wing phalanges.

The second fossil embryo has a similar story to tell. It's about 100 million years old, and is probably an embryonic Pterodaustro guinazui. This creature also lived in shallow waters, and had a long snout lined with thin filaments for filter feeding—it was a kind of flamingo of the Cretaceous. The details show that it too had a thin leathery eggshell.

Shell around a pterosaurian embryo from the Early Cretaceous period in Argentina (specimen MHIN-UNSL-GEO-V 246). a,b, Scanning electron micrographs of radial sections of the eggshell: note the nucleation centres and bladed crystals at the apex of the V-shaped eggshell units, and micrometre-sized vesicles (ghost protein) on the surfaces. c, Detail showing the eggshell and general preservation of the bones. Abbreviations: bc, bladed crystals; hum, humerus; mcIV, metacarpal IV; nc, eggshell nucleation centres; sh, eggshell; ves, vesicles.

Composite drawing of a pterosaurian embryo from the Early Cretaceous period in Argentina (specimen MHIN-UNSL-GEO-V 246). Abbreviations: bc, bladed crystals; co, coracoid; dv, dorsal vertebrae; fe, femur; ga, gastralia; hu, humerus; mc, metacarpal I–III; mcIV, metacarpal IV; mt, metatarsals I–IV; nc, eggshell nucleation centres; pm, premaxilla; ph1d4, first phalanx of wingfinger; ra, radius; sc, scapula; sk, skull; sh, eggshell; sv, sacral vertebrae; t, tarsals; ti, tibia; ul, ulna; ves, vesicles.

Chiappe LM, Codorniu L, Grellet-Tinner G, Rivarola D (2004) Argentinian unhatched pterosaur fossil. Nature 432:571-572.

Ji Q, Ji S-a, Cheng Y-n, You H-l, Lu J-c, Liu Y-q, Yuan C-x (2004) Pterosaur egg with a leathery shell. Nature 432:572.