Fossil specimens of Neotropical gymnotiform electric fishes from the Yecua Formation (Upper Miocene, Parana basin, Bolivia) are analyzed in the context of a comprehensive study of gymnotiform relationships. Each fossil is analyzed individually and placed in the phylogeny according to characters it actually possesses. Some of the fossils previously referred to Humboldtichthys kirschbaumi can be identified only as Gymnotiformes incertae sedis, others as incertae sedis within recognized suprageneric gymnotiform taxa. The holotype of H. kirschbaumi shares the presence of a striated opercle with some extant species of Sternopygus and Distocyclus and can be placed in the Recent gymnotiform family Sternopygidae; H. kirschbaumi is diagnosed by the presence of a deeply striated opercle in which the striations extend between the dorsal and ventral opercular ridge fields. The analysis indicates the presence of several taxa among the fossil material. The presence of a multispecies assemblage is not uncommon among Recent gymnotiforms inhabiting non-floodplain forest streams, the inferred preservational environment.
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Vol. 27 • No. 1