Mammal ancestors may have given live birth 90 million years earlier than we thought, rewriting evolutionary timelines

A dog-sized carnivore and mammal ancestor that lived around 236 million years ago seems to have given birth to live young, a new study suggests. This means the tactic of keeping young developing inside the mother ‪—‬ known as viviparity ‪—‬ may have emerged in the mammalian lineage 90 million to 95 million years earlier than scientists previously thought, researchers noted in the study.

"This is the first time that we have evidence on how these mammalian ancestors reproduced," said first author Leandro Gaetano, a paleontologist at Argentina's National Scientific and Technical Research Council. His team reported the findings Aug. 13 in the journal Frontiers in Mammal Science.