Even before the naming of Ionoscopiformes, the genera that make up the order would be closely placed to one another with the hypotheses by Maisey in 1991 along with Gardiner and coauthors in 1998. The order Ionoscopiformes would first be named by Lance Grande and William E. Bemis in a 1998 study focused on the phylogeny of
Amiidae along with fish that clades close to it. Within this publication, the order would contain three families: lonoscopidae, Oshuniidae, and Ophiopsidae. Within the publication, Oshuniidae and Ophiopsidae are placed as sister groups to one another with lonoscopidae being the outgroup. During this time, all of the families were poorly understood with Ophiopsidae being the only one of the three to contain more than one genus. This poor understanding of these groups would come in the form of one of the three families, Oshuniidae, being made invalid due to the type genus and only member of the family,
Oshunia, being reassigned to lonoscopidae. This grouping of two families within Ionoscopiformes would be generally accepted by most authors though papers such as one published by Machado in 2016 would begin to doubt if Ionoscopiformes was a true monophyletic clade. Below are the early phylogenic hypotheses mentioned. Another 2018 paper by Martin Ebert would echo this statement, placing Ionoscopidae at the base of Amiiformes and coining a new clade Ophiopsiformes as a new name for the order containing Ophiopsiellidae, a newly coined name for Ophiopsidae due to the fact that
Ophiopsis was found to not be a true member of the family. This would be countered in a publication by Guang-Hui Xu the next year that found a closer relationship between the two families, keeping both within Ionoscopiformes as pre-2018 papers had done. More recent papers such as the 2020 paper by Adriana López-Arbarello and coauthors do find Ionoscopiformes containing both lonoscopidae and Ophiopsiellidae as a true clade. This clade is considered to be the sister group to Amiiformes with the clade formed between the two orders being the sister group to the non-monophyletic 'Panxianichthiformes'. Below are the phylogenic hypotheses mentioned with Ionoscopiformes and Ophiopsiformes being shown as two separate orders where applicable. Ebert (2018) }} }} }} }} }} }}|style=font-size:85%;line-height:85%|label1=}} Xu (2019) }} }} }} }} }} }} }} }} }}|style=font-size:85%;line-height:85%|label1=}} López-Arbarello et al. (2020) }} }} }}
Internal relationships Though still controversial, there have been multiple papers describing ionoscopiforms that include phylogenies in more recent years such as in publications like the 2020 paper by López-Arbarello et al. and the 2019 paper by Xu, not many papers put a focus on the topic. The most recent paper to tackle with would be within a 2020 publication by Tamara El Hossny and coauthors that would test that phylogenic relationship between the members of the group along with the evolutionary history of Ionoscopiformes based on their cladogram. All three of these publications would find generally similar results with taxa such as Robustichthys, Asoalepidotus, Panxianichthys, and Subortichthys forming the outgroup before the main split between Ophiopsiellidae and Ionoscopidae. A new family Subortichthyidae would be coined in 2023 and would contain
Allolepidotus,
Eoeugnathus,
Sinoeugnathus, and
Subortichthys. Previously, another new family was established in 2017 by Louis Taverne and Luigi Capasso based on their newly described genus
Italophiopsis though neither the genus or family have been referenced in later publications on the order. Below are the cladograms from the publications mentioned. López-Arbarello et al. (2020) }} }} }} }} }} }} }} }} }} }}|style=font-size:85%;line-height:85%|label1=}} El Hossny et al. (2020) }} }} }} }} }} }} }} }} }} }} }} }} }}|style=font-size:85%;line-height:85%|label1=}} Feng et al. (2023) }} }} }} }} }} }} }} }} }} }} Another group rarely mentioned in the literature when mentioning ionoscopiforms is Furidae which has been referred to as 'ophiopsiforms' with short dorsal fins. This included the genera
Heterolepidotus,
Furo,
Ophiopsis, and
Brachyichthys. == Evolutionary history ==