Plagioscion peyeri, 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 : 10

Plagioscion peyeri n. sp.

Figure 5A–N

1998 Plagioscion sp. —Monsch: pl. 5, Fig. 23.

Holotype. Figure 5A–C , PIMUZ A/I 5062, Pebas Fm., middle Miocene, Iquitos (layer VI), Peru.

Paratypes. Five specimens: PIMUZ A/I 4992, 4993, layer I, PIMUZ A/I 5003, 5005, 5061, same data as holotype (layer VI) .

Etymology. Named after Bernhard Peyer (1885–1963), who together with Hans Bluntschli, collected the otoliths described here in 1912.

Diagnosis. OL:OH = 1.25–1.35. Ostium spatulate, distinctly inclined at 30–40°, relatively short. Downturned section of cauda gently curved, with its tapering tip pointing forward. Ostial–caudal interspace relatively wide, 30–35% of SuL. Umbo on outer face massive in large specimens, leading to OH:OT ratio of 1.5.

Description. Moderately large, compact, and robust otoliths up to 9.3 mm in length (holotype). Otolith thick, with significant ontogenetic thickening from OH:OT ratio of 2.5 at 5 mm length ( Fig. 6K–N ) to 1.5 at 9.3 mm

( Fig. 6A–C ). Dorsal rim shallow, slightly curved; ventral deeper, regularly curved or deepest below tip of cauda ( Fig. 6A ), probably an ontogenetic effect. Anterior rim blunt, rounded, rather thin in lateral view and hence rarely completely preserved. Posterior rim blunt, with distinctly inframedian, short and obtuse angular tip. All rims smooth, with dorsal rim sometimes slightly undulating.

Inner face bent only in horizontal direction and nearly flat in vertical orientation. Sulcus large, occupying much space of inner face and leaving little room above and behind cauda. Ostium moderately large, about as wide as high, OsL:OsH = 0.9–0.95, shallow, with small postostial lobe positioned high on posterior margin of ostium resulting in spatulate shape of distinctly downturned ostium. Cauda long, slightly deepened, distinctly and rather regularly curved with its tip pointing forward, caudal curvature index = 0.6–0.65. Narrow and indistinct dorsal depression above horizontal part of cauda extending to variable degrees behind downturned part of cauda. Ventral field smooth. Outer face with broad, smooth umbo, which massively increases in size with ontogenetic growth (compare Fig. 6B, E, H, J, L ).

Discussion. Plagioscion peyeri occurs more or less coeval to the marine Plagioscion marinus Aguilera & de Aguilera (2003) known from the Cantaure Fm. of Venezuela, the Castilletes Fm. of the Guajira Peninsula in Colombia,

and the Pirabas Fm. of Brazil. In fact, these two species are the most morphologically similar to the known fossil species of Plagioscion (see Aguilera et al., 2016 for figures). Plagioscion peyeri differs from P. marinus in being more compressed (OL:OH = 1.25–1.35 vs. 1.4–1.5), the wider ostial–caudal interspace (30–35% of SuL vs. 25–30% of SuL), and the very thick development of the umbo on the outer face in specimens larger than 8 mm in length. It could well represent the freshwater vicariant species of P. marinus and would then be the oldest freshwater record for the now exclusively freshwater genus.

Figures

Fig. 5 A–N, Plagioscion peyeri n. sp., A–C, holotype, PIMUZ A/I 5062; D–F, paratype, PIMUZ A/I 5005; G–H, paratype, PIMUZ A/I 5003; I–J, paratype, PIMUZ A/I 4992; K–N, paratype, 4993

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