The Origin of Lactation as a Water Source for Parchment-Shelled Eggs

  title={The Origin of Lactation as a Water Source for Parchment-Shelled Eggs},
  author={Olav T. Oftedal},
  journal={Journal of Mammary Gland Biology and Neoplasia},
  • O. Oftedal
  • Published 1 July 2002
  • Biology, Environmental Science
  • Journal of Mammary Gland Biology and Neoplasia
Available evidence indicates that mammary gland secretions first evolved in synapsids that laid parchment-shelled eggs. Unlike the rigid-shelled eggs of birds and some other sauropsids, parchment-shelled eggs lose water very rapidly when exposed to ambient air of lower vapor pressure, whether due to differences in relative humidity or to differences in temperature. This precludes endothermic incubation of parchment-shelled eggs in an open nest. Synapsids may have avoided egg desiccation by… 
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