Pachycormids apparently represent part of the first radiation of the total group of teleosts, and therefore are important in understanding stem teleost phylogeny. Gill rakers (or fanunculi) are elements of the gill skeleton (branchial basket) in fishes that function primarily to protect respiratory lamellae, and sometimes have a secondary role in feeding. Characteristics of gill rakers have been used for taxonomic diagnosis and cladistic analysis of the interrelationships of Pachycormiformes, with particular importance for Leedsichthys and Asthenocormus. The material on which these determinations have been based is reviewed, along with the validity of the use of gill rakers in analyses of extinct fishes in general, based on their utility in extant fishes, following the presentation of a standardized nomenclature for these structures. Gill rakers are demonstrated to be an unreliable source of taxonomic characters in suspension feeders. The assignment of specimen PETMG F34 to Leedsichthys, solely based on the presence of elaborated but dissimilar gill rakers, is rejected, as there are no osteological resemblances to any other specimen of that taxon. The characters used to erect Leedsichthys notocetes are demonstrated to be artifacts generated by erosion and fracture, and this material is consequently synonymised within Leedsichthys problematicus.
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