Pogonias tetragonus, Schwarzhans & Aguilera & Scheyer & Carrillo-Briceño, 2022

Pogonias tetragonus n. sp.

Figure 6A–L View Fig

Holotype. Figure 6A–E View Fig , PIMUZ A/I 5000, Pebas Fm., middle Miocene, Iquitos (layer VI), Peru.

Paratypes. Two specimens, PIMUZ A/I 5002, 5004, same data as holotype .

Further material. One poorly preserved, tentatively assigned specimen PIMUZ A/I 5066, same data as holotype, layer I .

Etymology. From tetragonos (Greek) = quadratic, referring to the nearly perfectly quadratic outline of the otolith.

Diagnosis. OL:OH = 1.12–1.22. Ostium wide, slightly inclined at 10–15°, with small postostial lobe, OsL:OsH = 0.95–1.05. Cauda slightly upward oriented before gently curving downwards, not reaching deeper than ostium, caudal curvature index 0.6. Ostial–caudal interspace 25–27% of SuL. Outer face flat, ornamented with irregular tubercles.

Description. Moderately large otoliths with nearly perfectly quadratic shape up to 5 mm in length (holotype); OH:OT = 2.2–3.3, depending on intensity of tubercles on outer face. Dorsal rim shallow, horizontal; ventral rim also nearly horizontal, slightly shorter than dorsal rim. Anterior and posterior rims nearly vertical slightly bent and slightly dorsally pronounced. All rims smooth or irregularly undulating, particularly dorsal rim.

Inner face distinctly convex in horizontal and vertical directions, with large sulcus occupying most of inner face. Ostium shallow, wide, large, nearly quadratic like outline of otolith, slightly inclined downwards. Cauda narrow, slightly deepened, with short, slightly upward-oriented anterior stretch and regularly curved, much longer downward-oriented section and running very close to posterior rim of otolith. Very narrow and indistinct dorsal depression above crista superior, which extends from rear part of ostium across horizontal part of cauda. Area behind cauda very narrow, smooth. Ventral field smooth. Outer face concave to flat, with several protruding tubercles ventrally in the largest specimen

( Fig. 6C–E View Fig ), resulting in a secondary thickening of the otolith. Outer face with numerous tubercles becomes increasingly prominent with size.

Discussion. Pogonias tetragonus is readily recognized by its nearly quadratic outline, which is also the main difference from the two extant species of the genus. Other differences are the lack of an expansion of the corner between dorsal and posterior rims and the relatively wide and slightly inclined ostium. Te two extant species of Pogonias ( P. cromis Linnaeus, 1766 and P. courbina [Lacépède, 1803]) have an antitropical distribution in the western Atlantic and are principally marine but may enter into brackish but not freshwater ( Froese & Pauly, 2021). However, the related monospecific genus Aplodinotus is today found exclusively in the freshwater systems of southeastern North America ( Schwarzhans, 1993). Pogonias tetragonus resembles the extant Aplodinotus grunniens Rafinesque, 1819 in the outline of the otolith but has a distinctly larger ostium and narrower ostialcaudal interspace (25–27% vs. 37% of SuL). Furthermore, the fossil otolith-based genus Frizzellithus shows some similarity and could also be related. Pogonias tetragonus differs from the more or less coeval marine Frizzellithus longecaudatus ( Nolf & Aguilera, 1998) from Colombia and Venezuela in the nearly flat ventral rim (vs. deeply curved), the cauda not extending beyond the ventral margin of the ostium, the narrower ostium, and the wider ostial–caudal interspace (25–27% vs. 17–22% of SuL). It thus appears that P. tetragonus is indeed best placed in the genus Pogonias , but it may not be directly related to the extant species. Instead, it might represent an extinct freshwater clade of the Pogonias group similar to Aplodinotus grunniens of North America.