Umbrina pachaula, 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 : 11-12

Umbrina pachaula n. sp.

Figure 6M–R

?1998 Umbrina sp. —Monsch: pl. 5, Fig. 24.

2016 Umbrina sp. —Aguilera, Schwarzhans & Béarez: pl. 5, Fig. 12–13.

Holotype. Figure 6M–N , PIMUZ A/I 4999, Pebas Fm., middle Miocene, Iquitos (layer I), Peru.

Paratypes. One specimen, PIMUZ A/I 5063, same data as holotype .

Additional material. One poorly preserved specimen, PIMUZ A/I 4995, same data as holotype .

Etymology. From pachaulos (Greek) = thick, bulky, referring to the broadly thickened outer face of the otolith.

Diagnosis (based solely on specimens from the Pebas Fm.). OL:OH = 1.2–1.35; OH:OT = 1.95–2.3. Ostium moderately wide, not inclined, with small postostial lobe, OsL:OsH = 1.05–1.1. Cauda regularly curved, reaching slightly beyond ventral margin of ostium, caudal curvature index 0.8–0.9. Ostial–caudal interspace 32–35% of SuL. Outer face broadly convex without distinct umbo, smooth.

Description. A relatively small, thick, massive otolith reaching about 5.5 mm in length (from Castilletes Fm.; holotype 3.1 mm). Dorsal rim shallow, nearly horizontal, with faint middorsal angle; ventral rim regularly curving but also relatively shallow. Anterior and posterior rims broadly rounded, nearly vertical, slightly dorsally pronounced. All rims smooth.

Inner face distinctly bent along horizontal axis and much less in vertical direction. Ostium moderately wide and about as wide as long. Cauda narrow, regularly bent, slightly curving towards the tip, running very close to posterior rim of otolith, and reaching very close to posterior ventral rim. Dorsal field very narrow, without marked dorsal depression. Ventral field smooth. Outer face smooth, distinctly convex, with almost the entire area thereof being occupied by broad umbo; only anterior tip of otolith somewhat thinning.

Discussion. Umbrina is a species-rich genus with many extant and fossil (otolith-based) species, particularly in the Americas ( Froese & Pauly, 2021). Te genus contains species with a flat outer face or marked postcentral umbo, but no species is known with an almost continuously and equally thickened outer face as is the case in U. pachaula . Other characters and proportions of otolith and sulcus in combination serve to differentiate U. pachaula from most other species, for instance the unusually wide ostial–caudal interspace, but are less conspicuous. Aguilera et al. (2016) reported few otoliths from the slightly older Castilletes Fm. of Colombia as Umbrina sp. , which resemble U. pachaula very much in all aspects including the characteristic thickening of the outer face; as a result, we now place them in the same species. Small differences in the curvature of the tip of the cauda are considered to represent intraspecific variability. Today, Umbrina spp. are strictly marine, and no species is known to occur in freshwater. Hence, U. pachaula would thus represent the only species that occurred in both marine–estuarine and freshwater environments in the late early to middle Miocene. Its occurrence in the Castilletes Fm. is indeed near the mouth of the Pebas Wetland System to the Atlantic. We interpret U. pachaula as a marine species that was able to migrate upstream into freshwater environments.

Remarks: Tree otoliths in Bluntschli and Peyer’s collection are too poorly preserved to allow identification (PIMUZ A/I 4997, 5007, and 5064) ( Table 2).

Figures

Fig. 6 A–L, Pogonias tetragonus n. sp., A–E, holotype, PIMUZ A/I 5000; F–J, paratype,PIMUZ A/I 5002; K–L, paratype, PIMUZ A/I 5006.M–R, Umbrina pachaula n. sp., M, N, holotype, PIMUZ A/I 4999; O–R, paratype, PIMUZ A/I 5063. S–T, Sciaenops? sp., PIMUZ A/I 5065