Diaphorocetus was originally named Mesocetus by Moreno. Lydekker found that Mesocetus was already in use for an extinct mysticete, so he renamed the sperm whaleHypocetus. Ameghino too recognized Moreno's name as preoccupied, but unaware of Lydekker's paper, coined his own replacement nameDiaphorocetus for Mesocetus. Diaphorocetus was declared a nomen protectum by Paolucciet al. because Hypocetus and Paracetus have not been used as valid since 1899 under Article 23.9 of the Code.