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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.
Based on fossil evidence, the earliest known true primates, represented by the genus Teilhardina, date to 55.8 million years old. An early close primate relative known from abundant remains is the Late Paleocene Plesiadapis, c. 55â58 million years old.