An Exceptionally Preserved Fossil Fish from the Silurian of China Illuminates Jaw Evolution

Osteichthyans(bony fishes and tetrapods)have the maxillary,premaxillary,and dentary bones,all with facial laminae,whereas placoderms(jawed stem gnathostomes)have supposedly nonhomologous gnathal plates that lack facial laminae.The discovery of Entelognathus from the Late Silurian(Ludlow)Xiaoxiang vertebrate fauna of Yunnan,China in 2013,revealed the presence of maxilla,premaxilla,

Osteichthyans （bony fishes and tetrapods） have the maxillary, premaxillary, and dentary bones, all with facial laminae, whereas placoderms （jawed stem gnathostomes） have supposedly non- homologous gnathal plates that lack facial laminae. The discovery of Entelognathus from the Late Silurian （Ludlow） Xiaoxiang vertebrate fauna of Yunnan, China in 2013, revealed the presence of maxilla, premaxilla, and dentary, supposedly diagnostic osteichthyan bones, in a placoderm near the crown gnathostome node. However, the relationship between these marginal jaw bones and the gnathal plates of conventional placoderms remains uncertain.