This year's version of the new coin in the "Evolution of Life"  series features the Synapsida. Synapsids are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes reptiles and birds. The group includes mammals and every animal more closely related to mammals than to sauropsids.[6] Unlike other amniotes, synapsids have a temporal fenestra, an opening low in the skull roof behind each eye orbit, leaving a bony arch beneath each; this accounts for their name. The distinctive temporal fenestra developed about 318 million years ago during the Late Carboniferous period,[1] when synapsids and sauropsids diverged, but was subsequently merged with the orbit in early mammals. This unique coin depicts a rose gold-covered skeleton.