Cichlasoma bluntschlii, Schwarzhans & Aguilera & Scheyer & Carrillo-Briceño, 2022

Schwarzhans, Werner W., Aguilera, Orangel A., Scheyer, Torsten M. & Carrillo-Briceño, Jorge D., 2022, Fish otoliths from the middle Miocene Pebas Formation of the Peruvian Amazon, Swiss Journal of Palaeontology (2) 141 (1), pp. 1-15 : 5-6

Cichlasoma bluntschlii n. sp.

Figure 3A–D

Holotype. PIMUZ A/I 4996, Pebas Fm., middle Miocene, Iquitos (layer I), Peru.

Etymology. Named after Hans Bluntschli (1877–1962), who together with Bernhard Peyer, collected the otoliths described here in 1912.

Diagnosis. OL:OH = 1.15; OH:OT = 2.8. Outline nearly rhomboid with short rostrum, rounded posterior tip, middorsal and midventral angles. Ostium slightly upward directed at 15°; cauda with widened, flexed tip at 45°. CaL:OsL = 1.1; OsH:CaH = 1.5. Dorsal depression and ventral furrow distinct.

Description. A single, very well-preserved otolith of 2.2 mm in length, which is morphologically mature when compared to extant cichlid otoliths. Sulcus outline rhomboidal. Dorsal rim nearly straight and ascending from rostral tip to middorsal angle and slightly bent from middorsal angle to posterior tip; ventral rim slightly deeper than dorsal rim high, with rounded midventral angle. Rostrum moderately long, 15% of OL, with rounded tip; no excisura or antirostrum. Posterior tip slightly higher than rostrum, more distinctly rounded. All rims slightly and irregularly undulating.

Inner face strongly convex, with slightly supramedian and deepened sulcus. Ostium slightly bent upwards anteriorly, distinctly wider and slightly shorter than cauda, with well-defined ostial colliculum. Cauda narrower, slightly longer, very slightly upward oriented in its anterior two-thirds at about 5°, curved towards ventral at its posterior third at 45°, and slightly widened towards its rounded tip. Dorsal depression small but distinct, with marked crista superior towards sulcus. Ventral furrow very distinct, running moderately close to ventral rim of otolith. Outer face flat, nearly smooth, with few faint radial furrows on the ventral and dorsal fields.

Discussion. Te family Cichlidae represents an important and large group in today’s tropical South American freshwater regime, and, after characids and loricariids, the Neotropical cichlids, with at least 44 genera and more than 290 species, constitute the third speciose group of freshwater fishes in South America (see van der Sleen & Albert, 2018). According to van der Sleen and Albert (2018), the genus Cichlasoma is represented by at least 12 species in the Amazon and Orinoco basins and coastal rivers of the Guianas and Trinidad. Otoliths are only known from a fraction of these, but it is highly unlikely that the Pebas Wetland System contained any fish species, which would be still present today. Te cichlid otolith described here is regarded as typical due to the organization of the sulcus, which is characterized by the upward-oriented ostium and the broadened, downwardturned rounded caudal tip at an angle between 30° and 50°. In addition, the distinct dorsal depression and ventral furrow add to the characterization. Of the known extant otoliths, those of Cichlasoma most closely resemble the shape and proportions of the otolith described here. For comparison, an otolith of the extant Cichlasoma dimerus ( Heckel, 1840) is figured ( Fig. 4E ; reproduced from Lombarte et al., 2006). Note that the dorsal depression and the ventral furrow are less clearly visible in the photograph of the extant specimen due to its semi-transparent nature. Cichlasoma bluntschlii differs from C. dimerus in the higher body and marked middorsal angle, as well as the absence of an excisura. Cichlasoma bluntschlii represents the first fossil otolith record in the world of the family ( Nolf, 2013) and the first record of the genus as well.

Figures

Fig. 3 A–D Cichlasoma bluntschlii n. sp., holotype, PIMUZ A/I 4996;E Cichlasoma dimerus (Heckel, 1840), freshwater from Argentina, refigured from Lombarte et al., 2006; F–G, Percoidei indet., PIMUZ A/I 4994

Fig. 4 A–E, Pebasciaena amazonensis n. gen. et n. sp., PIMUZ A/I 5006