‘Jurassic Mother’ Is Our Earliest-Known Mammal Ancestor
Researchers have now found a well-preserved fossil of the earliest known member of the animal group that encompasses today’s placental mammals, which includes humans. The shrew-like creature, named Juramaia sinensis, or “Jurassic mother from China,” dates back to 160 million years ago, 35 million years earlier than the oldest mammal fossil previously discovered. The Nature study gives some tangible support to genetic evidence suggesting that the two main types of mammals split well before the previous oldest mammal fossils.
Zhe-Xi Luo, a paleontologist at the Carnegie Museum of Natural History in Pittsburgh, and his colleagues analyzed the Juramaia fossil, which was unearthed in China’s northeast Liaoning Province, a hotspot for paleontology. The fossil consisted of an incomplete skull, a partial skeleton, a full set of teeth, and impressions of residual soft tissues like hair.
After comparing the fossil’s features with those of other ancient mammals, the researchers placed Juramaia among the eutherians, a group that includes placental mammals and their progenitors, rather than the marsupial group, the metatherians.