Taxonomic assessment of body scales of Cichlidae (Teleostei)
Final Report Abstract
The family Cichlidae is a diverse group of tropical freshwater fishes that includes four subfamilies (Etroplinae, Ptychochrominae, Cichlinae, Pseudocrenilabrinae) and probably more than 2.200 species. The study of fossil cichlids is an essential contribution to understanding the evolution of this fish family, which probably originated in the Upper Cretaceous or at the beginning of the Cenozoic. However, only about 30 fossil cichlid species have been described so far, and it can be assumed that the actual species diversity of the fossil record was much higher. One of the reasons why so few species have been described lies in the difficult taxonomic assignment of fossil material, since the skeletal architecture of cichlids follows a conservative bauplan and synapomorphies of recent genera/tribes mostly affect soft tissue structures that are not preserved in fossils. The overall objective of this project was to investigate the taxonomic value of cichlid scales and to create a representative data set based on the scales taken from recent cichlids. Background and motivation were grounded on a literature survey suggesting a taxonomic relevance of scales and the fact that scales are often well preserved in fossil cichlids. Due to the thematic focus of the applicant's working group and due to the availability of comprehensive, ethanol-fixed material in the Ichthyological Collection of the Zoological State Collection Munich, the focus of the project was on African cichlids (subfamily Pseudocrenilabrinae). Overall, scales of 88 cichlid species were investigated including 79 species from 60 genera of the Pseudocrenilabrinae (with representatives of all 27 tribes) and nine species from eight genera of the three other subfamilies. The entire material included 1.729 scales from a total of 145 fish individuals. Scales were extracted from distinct regions of the flank according to a standardised protocol; care was taken to ensure that the sampled specimens were adult or at least subadult individuals. For each species, overall scale shape, type of radii, number of radii and focal position (focal index) were documented, and relative scale length and width (in relation to the standard length of the fish) were measured. All scales were documented photographically and four representative scales of each species were mounted on totally 18 photo plates. To explore differences in scale characters within and between species/genera and tribes, statistical analysis using the PAST software was done. Scale descriptions, photo plates and statistical analyses will provide the basis for the 'Cichlidae fish-scale atlas' to be created in accordance with the objectives of the project, which unfortunately could not be finished in the reference period, but whose completion is imminent. Our 'Cichlid fish-scale atlas' will be a valuable data resource for future taxonomic analyses of fossil cichlids from Africa, which will considerably facilitate the taxonomic determination of fossil cichlids, and, in addition, can also contribute to the classification of new species of extant cichlids.
Publications
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First scale-atlas for cichlid fishes. – Abstract Volume of the 93rd Annual Meeting of the Paläontologische Gesellschaft, Stuttgart, Germany, 19–23 September 2022, p. 54. [oral presentation]
Penk, S.B.R. & Reichenbacher, B.
