Eutheria (; from Greek-, eu- "good" or "right" and , th?ríon "beast" hence "true beasts") is one of two mammalian clades with extant members that diverged in the Early Cretaceous or perhaps the Late Jurassic. All placental mammals are eutherians. Extant eutherians, their last common ancestor, and all extinct descendants of that ancestor are members of Placentalia.
Eutherians are distinguished from noneutherians by various phenotypic traits of the feet, ankles, jaws and teeth. All extant eutherians lack epipubic bones, which are present in all other living mammals (marsupials and monotremes). This allows for expansion of the abdomen during pregnancy.
an enlarged malleolus ("little hammer") at the bottom of the tibia, the larger of the two shin bones
the joint between the first metatarsal bone and the entocuneiform bone (the outermost of the three cuneiform bones) in the foot is offset farther back than the joint between the second metatarsal and middle cuneiform bones--in metatherians these joints are level with each other
The fossil eutherian species believed to be the oldest known is Juramaia sinensis, which lived about 160 million years ago.Montanalestes was found in North America, while all other nonplacental eutherian fossils have been found in Asia. The earliest-known placental fossils have also been found in Asia.
Simplified, non-systematic, outline of evolution of eutheria from cynodont therapsids. + = extinct
^Rook, Deborah L.; Hunter, John P. (April 2013). "Rooting Around the Eutherian Family Tree: the Origin and Relations of the Taeniodonta". Journal of Mammalian Evolution. 21: 75-91. doi:10.1007/s10914-013-9230-9.