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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.
Plesiadapiformes is an extinct order of mammals which is either closely related to primates or a precursor of them. They first appear in the fossil record between 65 and 55 million years ago. It is thought that these were the first mammals to have developed finger nails in place of claws. Based on fossil evidence, the earliest known true primates were represented by the genus Teilhardina date to 55.8 million years old. This was a marmoset like primate that lived about 56-47 million years ago. Archicebus is a genus of primate also from around 55 million years ago.