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extinct group of mammals that includes the ancestral forms of later, more advanced ungulates (that is, hoofed placental mammals). The name Condylarthra was once applied to a formal taxonomic order, but it is now used informally to refer to ungulates of Late Cretaceous and Early Paleogene times. Their greatest diversity occurred during the Paleocene Epoch (65.5-55.8 million years ago), but similar forms persisted into the middle of Oligocene Epoch and died out about 30 million years ago.