Splenial

The splenial is a small bone in the lower jaw of reptiles, amphibians and birds, usually located on the lingual side (closest to the tongue) between the angular and surangular.^[1][2] The splenial and coronoid are together known as the paradental elements.^[3] In non-tetrapod vertebrates, the splenial is known as the first infradentary and forms part of the infradentary series along with the postsplenial and angular.^[4][5] The earliest known taxon with infradentary bones is the placoderm Entelognathus, while they were absent in the earlier-diverging Qilinyu.^[6] Splenials are present in non-mammalian synapsids, but lost in mammals, though there are some claims of a vestigial splenial in some early mammals.^[3]