In 2011, paleontologists Junchang Lü, David Unwin, and colleagues at the Chinese Academy of Geological Sciences uncovered a fossil that sheds light on our understanding of pterosaurs, the flying reptiles of the Mesozoic Era. The fossil: an adult female Darwinopterus, which appears to be in the act of laying an egg. Although blog author Darren Naish notes the improbability that this fossil portrays the actual moment of giving birth (Naish proposes that the egg likely slipped from the mother’s body as she decomposed), the discovery provides us with new insights into the behavior and traits of the pterosaur.

Darwinopterus, a Jurassic pterosaur, is important for its intermediate position on the evolutionary tree. Darwinopterus has the long fifth toe and lengthy tail of the early rhamphorhynchid pterosaurs, yet the large skull and long neck of the pterodactyloids, a more diverse group which first appeared in the Middle Jurassic.

Like the eggs of some modern reptiles and other pterosaur eggs that scientists have found, the egg that Lü and Unwin discovered has a soft shell. Pterosaurs, with their soft-shelled eggs, are situated on the evolutionary tree between crocodilians and dinosaurs, both of which, interestingly, lay eggs with hard shells. This raises questions of origin: Did all pterosaurs lay soft-shelled eggs? Were hard-shelled eggs the ancestral condition, or did they evolve independently in both crocodilians and dinosaurs? If hard-shelled eggs were the ancestral condition, what provoked the evolution of soft-shelled eggs in the pterosaurs?

Because soft-shelled eggs dry in the heat of the sun, Naish suggests that Darwinopterus might have buried its eggs, like many species of birds and reptiles do to prevent dessication. Furthermore, by contrasting the physiology of the fossilized embryo with that of its mother, Naish infers that juvenile pterosaurs, with their smaller size and different skull shape, likely occupied a distinct ecological niche from their adult counterparts, taking advantage of different habitats and resources for survival. Naish also reckons that these young pterosaurs were superprecocial – that flaplings, shortly after hatching, would have been entirely able to fend for themselves. Hopefully, future discoveries will grant us a greater understanding of the life habits of these fascinating creatures.

Find Darren Naish’s original blog article at Scienceblogs.com.

Read the original publication in Science.

Published On: November 19, 2012

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