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Maintained by pioweb@ucsc.edu. The common ancestor of placental mammals probably looked like Eomaia scansoria, the earliest known placental mammal, shown here in an artist's reconstruction based on a 125-million-year-old fossil skeleton found in China in 2002.aintained by pioweb@ucsc.edu. The common ancestor of placental mammals probably looked like Eomaia scansoria, the earliest known placental mammal, shown here in an artist's reconstruction based on a 125-million-year-old fossil skeleton found in China in 2002.
As mentioned above, the first mammals evolved toward the end of the Triassic period from therapsids, the line of mammal-like reptiles that arose in the early Permian period and produced such uncannily mammal-like beasts as Thrinaxodon and Cynognathus.