Various suggestions had been put forward including that the choana was homologous to either the posterior or anterior nostril of non-tetrapods, that it had ‘budded off’ from one of these passages, or that it was an entirely novel form, unrelated to either of the other nostrils.
Various theories were put forward regarding the choana's evolutionary history and its relationship to other nasal structures. These include the idea that it might be homologous to either the posterior or anterior nostril of non-tetrapods, that it may have originated from one of these passages, or that it is a completely novel structure unrelated to any existing nostrils.