A 236-million-year-old fossil could rewrite the story of mammalian birth
Scientists may have uncovered evidence that a mammal ancestor was giving birth to live young 236 million years ago. A fossilized cynodont showed a neonatal growth line and an unusually large birth size that closely match patterns seen in modern mammals. The discovery could push the evolution of live birth back by up to 95 million years. It also raises the possibility that many supposedly “modern”…
A 236-million-year-old fossil may challenge the understanding of mammalian birth. A study in Frontiers in Mammal Science presents evidence that some cynodonts, early mammalian ancestors, may have given birth to live young. Dr. Leandro Gaetano from Argentina's CONICET explains that this implies viviparity among early cynodonts originated 95 to 90 million years earlier than previously thought.
The investigation began with an unusual growth mark in a C. theotonicus fossil found in northwestern Argentina. Researchers estimated the animal's newborn weight, which was about 1.7kg, and compared it to its adult weight of roughly 12kg. This neonate-adult body mass ratio of 14% is striking when compared to living reptiles and birds.
If this trait was present in cynodonts, it suggests live birth may have been a more common trait in early mammalian ancestors than previously believed.
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