Descrição osteológica da piranha amarela (Characiformes: Serrasalmidae: Serrasalmus maculatus)

Abstract

Serrasalmus maculatus has a wide distribution across the Neotropical region, being found in several rivers of the Amazon and Paraná-Paraguay basins, inhabiting still-water environments near aquatic vegetation. Described from the Guaporé River, it was identified as S. spilopleura in the upper Paraná River basin until 2007. The presence of a dark subterminal band on the caudal fin differentiated it from S. spilopleura, which has a black distal margin. Molecular studies have shown that the genetic variability of this species is extremely high, reflecting the diversity of its geographical distribution and the complex taxonomy of the genus, indicating a species complex with at least one new species. Thus, this study aimed to describe the osteology of S. maculatus specimens from the upper Paraná River basin to support future investigations into the taxonomy and phylogeny of this species. The osteological analyses were conducted by preparing two dry skeletons using dermestid beetles and two cleared and stained specimens. Notable features include a neurocranium with a triangular shape in lateral view, a supraoccipital region with a smooth demarcation, and a frontal region surrounding the first fontanel, which has a triangular shape. Additionally, the species has 35-37 total vertebrae, including four fused to the Weberian apparatus, as well as 19-23 pre-pelvic and 8-10 post-pelvic spines on the abdominal keel. Therefore, this study provided baseline material for future osteological comparisons of the upper Paraná River population, potentially aiding in the diagnosis and description of new species.