part of part of overlaps overlaps in taxon adjacent to adjacent to Mammalia Sarcopterygii Aves tetrapod frontal bone lacrimal bone orbit of skull dermatocranium facial bone dermal bone prefrontal bone http://upload.wikimedia.org/wikipedia/commons/4/44/Dromaeosaurus_skull_en.svg Wikipedia:Prefrontal_bone A bone separating the lacrimal and frontal bones in many tetrapod skulls. prefrontal AAO:0000460 It first evolved in the sarcopterygian clade Rhipidistia, which includes lungfish and the Tetrapodomorpha. The prefrontal is found in most modern and extinct lungfish, amphibians and reptiles. It is very small, fused to the frontals or lost in many groups of coelurosaurian theropod dinosaurs and is completely absent in their modern descendants, the birds. The prefrontal was also lost in early mammaliaforms and so is not present in modern mammals either UBERON:0010750 facial skeleton