Systematic Review and Cranial Osteology of Petersius with Redescription of P. conserialis (Teleostei: Alestidae) from the Rufiji and Ruvu Rivers of Tanzania

Abstract

We review the systematics of the monotypic alestid genus Petersius and provide a taxonomic redescription of P. conserialis from eastern Tanzania. Morphological investigation includes direct observation and examination of radiographed and µCT-scanned data from type and non-type specimens. We delimit the taxon's geographic distribution along the lowland regions of the Rufiji and Ruvu river basins in Tanzania and provide information on ecology, sexual dimorphism, and ontogenetic variation. Petersius is herein diagnosed by the possession of a unique cuspidation patterning of the inner-row premaxillary dentition and a distinctively shaped anterodorsal margin of the supraoccipital crest. It shares with some species of Phenacogrammus a sigmoid-shaped process on the dorsal margin of the second infraorbital, a feature lacking in other alestid taxa. Additional features of potential utility for ongoing investigation of relationships among alestid genera include the possession of contralateral premaxillae separated by the anteromedial process of the mesethmoid and without interdigitations connecting the medial surfaces of the premaxillae; four, occasionally five or six, small outer-row premaxillary teeth implanted alternately with those of the inner row; a dentary lacking a pair of conical inner-row teeth proximal to the symphysis; a dorsal posttemporal fossa that is smaller than the ventral fossa; a median third posttemporal fossa located entirely within the epioccipital; a truncate dorsomedial cranial fontanel; and a complete circumorbital series forming an uninterrupted ring around the orbit in adult specimens. AMERICAN MUSEUM NOVITATES NO. 3992

Phylogenomics and Morphology of the African Fish Genus Brycinus with Revalidation of Brachyalestes and Description of a New Species from the Congo Basin (Teleostei: Alestidae)

“…Morphological approach.— Counts and measurements follow Stiassny et al (2021) and Melo and Stiassny (2022). Point-to-point linear distances were measured using digital calipers with a precision of 0.1 mm.…”

“…The first primary calibration is represented by the earliest reported alestid teeth from the Ager basin (Eocene 54–49 Ma) of Spain (de la Peña Zarzuelo, 1996). Similarities between the fossil dentition and that of modern Alestes , Brycinus s.s., Brachyalestes , and Bryconaethiops (Melo and Stiassny, 2022) necessitated a conservative placement at the most recent common ancestor (MRCA) at the node including all sampled alestids (mean = 51.9; sigma = 2.0; 95–5% quantiles: 55.2–48.6). The second primary calibration corresponds to the highly distinctive, earliest fossil teeth of Hydrocynus , from the Dur At-Talah deposit (Eocene 48.6–33.9 Ma) of Libya (Otero et al, 2015).…”

“…Freshwater fishes of the family Alestidae constitute by far the greatest diversity of African characiforms, with current estimates of 118 species distributed among 19 genera with species found throughout Africa's freshwater ecosystems (Froese and Pauly, 2019; Fricke et al, 2022). Despite significant progress toward the resolution of interfamilial, suprageneric, and generic groupings, much uncertainty remains (Murray and Stewart, 2002; Calcagnotto et al, 2005; Hubert et al, 2005; Arroyave and Stiassny, 2011; Melo and Stiassny, 2022). This is particularly true for the largest alestid genus, Brycinus , and a lack of consensus regarding the systematics of this species-rich and morphologically heterogeneous assemblage is in many respects emblematic of ongoing uncertainties surrounding the systematics of Alestidae as a whole.…”