Abstract
Although the vast majority of fossil catfish material is isolated elements such as fin spines, a number of fossil catfishes (Siluriformes) have been named based on articulated crania from Palaeogene formations of Africa. The fossil taxa from marine sediments have been assigned to the extant marine family Ariidae, or have been assumed to have washed into marine sediments from freshwater habitats. The ability to assess the relationships of these fossils without reference to the nature of the geological sediments may provide insight into the history of these families. Most of the taxonomic work on the 11 catfish families found in Africa has focused on soft-tissues or DNA, which is problematic for the fossil material. Here we provide osteological features to distinguish families of African catfishes; eight of the families that are likely to be found in fossiliferous deposits can be distinguished based on a combination of skull features including the morphology of the cranial fontanelle, mesethmoid, and dermal ornamentation. We reassess the familial placement of the Palaeogene catfishes. We find that †Eomacrones wilsoni, from the Palaeocene of Nigeria, belongs in Bagridae s.s. This confirms that bagrids were in Africa much earlier than the Miocene. Because this catfish comes from Palaeocene marine sediments, the biogeographic history of Bagridae needs to be reassessed to consider marine dispersal in this taxon.
Highlights
Catfishes (Siluriformes) are well represented in African fossiliferous deposits of the Cenozoic
As noted in the Introduction, there are three Palaeocene and ten Eocene species named for fossil catfish crania, placed in seven fossil and three extant genera
There is a notch in the posttemporal, as noted by Longbottom (2010) but this appears to be an autapomorphy of the species. †Nigerium wurnoense and †‘N’. gadense are represented by fewer specimens, of which one of each were figured by Longbottom (2010: plate 3); specimens were examined by one of us (AMM)
Summary
Catfishes (Siluriformes) are well represented in African fossiliferous deposits of the Cenozoic. Many elements of catfish skeletons are quite distinctive compared with many other fish taxa, allowing relatively easy identification of fossils at an ordinal level. Dorsal and pectoral fin spines may be diagnostic for a genus or family (e.g., Gayet and Van Neer 1990), but researchers have assigned the vast majority of isolated elements to the lowest taxonomic level possible (usually family or genus) and have not named them as new taxa. Catfish specimens that are preserved in partial articulation, mostly three-dimensional crania, can be distinguished from one another and extant forms, and many of these have been described and named as unique species or genera (e.g., Stromer 1904; Peyer, 1928; Murray and Budney 2003; Otero et al 2007; El-Sayed et al 2017). Several named catfishes are known from Palaeogene deposits of Africa, in particular from Nigeria and Tanzania, as well as the Fayum Depression of Egypt
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