Dercetidae

Before the naming of the family, multiple genera that have been placed within Dercetidae were placed within a group referred to as Sclerodermis until Arthur Smith Woodward would coin the name Dercetidae in 1901.^[1] He would place the family close to the other more elongate fish families Halosauridae and Notacanthidae.^[2] This, however, was only based on a number of more basic similarities such as the elongated skulls and postcrania of the two groups.^[1] This classification would change in 1969 when Peter Charles Goody would place the family, along with multiple other closely related families, into Salmoniformes due to some features such as the shared features of adipose fins and features of the fins. A close relationship between the family and Cimolichthyidae was also suggested due to the similar long bodies and the presence of scutes on the sides of the fish. This would change in 1973 when D. E. Rosen would erect the new order Aulopiformes and place Dercetidae along with its relative into the suborder Alepisauroidei.

In more recent publications, the monophyly of Dercetidae has been questioned due to the lack of defining characters that is shared by all members of the family. Some previous characters, such as those relating to the overall shape of the head, were found to be present in other aulopiforms. A paper by Oksana Vernygora and coauthors would suggest that the main character of the group could be the reduction in neural spines but this would later be argued against in a 2021 paper by Jesús Alvarado-Ortega and Jesús Alberto Díaz-Cruz. These authors would suggest that this feature was more likely a homoplastic feature rather than one that could be a feature that could define the clade.^[1] Even with this being the case however, the publication would find that Dercetidae is a monophyletic clade.^[3] A 2025 paper by Valéria Gallo and colleagues would build upon this with the description of the genus Antarctichthys which contained a phylogeny with a focus on Dercetidae. Both this paper and the previous one by Alvarado-Ortega and Díaz-Cruz would use a phylogeny originally in a 2011 publication by Hilda Silva and Valéria Gallo. This matrix would be modified in the 2021 publication and would be edited again in the 2025 paper to remove 23 characters that did nothing at the family level. Below is the cladogram generated using Implied Weighted Maximum Parsimony Analysis in the 2021 paper along with the single cladogram from the 2025 publication.^[3][4]

Members of Dercetidae are generally known to be marine fish with long, shallow bodies with similarly long skulls. In some genera, such as Antarctichthys and Rhynchodercetis, the upper jaw would extend past the lower one and form a snout.^[4] Though not a trait in every genus assigned to the family, the maxilla and mandible each possess a single row of small teeth with these being absent vomer and sometimes the premaxilla.^[5] One of the few exceptions to this is Antarctichthys, which lacked teeth on both the top and bottom dentition.^[4][6]

Similar to other enchodontoids, dercetids were generally small though large members such as Dercetis magnificus, a fish with a standard length of over 1 metre (3.3 ft), are present in the clade.^[1] Another feature that all members share is the lack of scales outside of large ones, commonly referred to as scutes, that ran down the length of the body with these forming one to three rows depending on the species.^[6] Though still argued against by some authors, a defining feature of all dercetids is the reduced neural spines with them being equal to or less than the total vertebral length.^[4]