Millerettids are an extinct group of anapsids known from the Upper Permian (about 240 million years ago) of South Africa. Early in this century, millerettids were believed to be related to lepidosaurs (lizards, snakes, the tuatara, etc.) because they were small, possibly insectivorous animals with a lightly built skeletons. However, millerettids are now asserted to be more closely related to turtles than to the diapsids.
Some millerettids have a temporal fenestra like synapsids (mammals and their fossil relatives) do, but this fenestra was acquired independently according to phylogenetic analyses. The presence of a quadrate emargination (a concave area at the back of the skull) suggests that millerettids had a tympanum (ear drum) and could hear high frequency airborne sounds. However, their stapes (the sound-conducting middle ear ossicle) is still robust, suggesting that their auditory acuity was not as good as in more recent groups of anapsids ( procolophonoids and turtles).