Affiliation:
1. Departamento de Zoologia Universidade do Estado do Rio de Janeiro Rio de Janeiro Brazil
2. UMR 8067, Département Adaptations du Vivant Muséum National d'Histoire Naturelle Paris France
3. UMR 7262 PALEVOPRIM CNRS, UFR SFA Université de Poitiers Poitiers France
Abstract
AbstractMany actinopterygian fish groups, including fossil and extant polypteriforms and lepisosteiforms, fossil halecomorphs, and some basal teleosts, have stout bony scales covered by layers of ganoin—an enamel layer ornamented with minute tubercles. Ganoid scales preserve well as disarticulated remains and notably constitute most of the fossil record for polypteriform in both South America and Africa. Based on two variables (tubercle size and distance between tubercles), some authors reported that the ganoin tubercle ornamentation in these scales is constant within a species and differs between species and allows distinguishing species or at least groups of species. However, despite its promising potential for assessing polypteriform paleodiversity, this tool has remained unused, probably because the variables are not well defined, and intraspecific variation does not seem to have been considered. To address this gap, we aimed to test the intraspecific and intra‐individual variation in the ornamentation of ganoid scales in the type species Polypterus bichir. We propose three different parameters to describe the tubercle ornamentation: the distance between contiguous tubercles centers, their density, and their relative spatial organization. With these parameters, we investigate the variation in ganoin ornamentation among four specimens and across different regions of the body. Our results show that the distribution of the tubercles is highly variable within a same species, regardless of the body region, and sometimes even between different sectors of a same scale. Moreover, the variation observed in P. bichir overlaps with the distribution described in the literature for several extant and fossil species. Thus far, the ornamentation of ganoid scales is not a reliable diagnostical feature for polypterids.
Funder
Conselho Nacional de Desenvolvimento Científico e Tecnológico
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro
Centre National de la Recherche Scientifique