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Hard evidence from soft fossil eggs

It is thought that dinosaurs laid hard-shelled eggs, whereas ancient marine reptiles gave birth to live young. However, new discoveries of fossilized soft-shelled eggs challenge these long-held tenets of reproductive evolution.
  1. Johan Lindgren

    1. Johan Lindgren is in the Department of Geology, Lund University, 223 62 Lund, Sweden.

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  2. Benjamin P. Kear

    1. Benjamin P. Kear is at the Museum of Evolution, Uppsala University, 752 36 Uppsala, Sweden.

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The appearance of the amniotic egg marks a key event in the evolutionary history of vertebrates. Its major adaptive advantage is the amnion — an enclosing membrane that prevents the embryo from drying out, and the principal feature to which the amniotic egg owes its name. Another crucial development was the addition of a tough outer shell that provides protection and mechanical support. This allowed the first reptiles to colonize terrestrial environments more than 300 million years ago, and paved the way for the rise of birds and mammals.

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Nature 583, 365-366 (2020)

doi: https://doi.org/10.1038/d41586-020-01732-8

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