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| This composite photo shows an isolated mesosaur embryo with an adult mesosaur to show the size relation. CREDIT: Graciela Pineiro |
Despite evidence that the earliest examples of creatures such as mammals and reptiles gave birth to live young, they actually may have laid eggs, a scientist argues.
"These eggs are probably out there, but nobody has looked hard enough for them or they have not been recognized," says University of Bonn, Germany, paleobiologist P. Martin Sander, who details his analysis in the Aug. 17 issue of the journal Science.
Both mammals and reptiles envelop their developing embryos in protective layers, something that ultimately helped their ancestors conquer the land and that still helps their offspring survive. Mammals often keep these membrane-bundled offspring within them, giving birth to live young, while reptiles generally lay their membrane-swaddled progeny in eggs.
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