The Fossil Record
What is Evolutionary History?
Cleavage and Blastulation
Cloning of Dolly the Sheep
Fertilization
Conditions on Early Earth
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Updated: Dec 18, 2025

Windowing Chicken Eggs for Developmental Studies
Published on: October 1, 2007
Mark A Norell1, Jasmina Wiemann2, Matteo Fabbri3
1Division of Vertebrate Paleontology, American Museum of Natural History, New York, NY, USA. norell@amnh.org.
The first dinosaur eggs were soft-shelled, challenging previous assumptions based on modern birds and reptiles. This discovery suggests hard-shelled dinosaur eggs evolved multiple times independently.
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