Aplodinotus distortus Nolf 2003

Aplodinotus distortus Nolf, 2003 Fig. 26J–M Material examined UNITED STATES OF AMERICA – Mississippi • 19 sagittae; Catahoula Formation; MMNS VP-7449, MMNS VP-7461, MMNS VP-7456.1 (Fig. 26L–M), MMNS VP-8002.2, MMNS VP-8200.2, MMNS VP-8201.2, MMNS VP-8712 (8 specimens), MMNS VP-7458.1 (Fig. 26J–K), MMNS VP-7458.2, SC 2013.28.760, SC 2013.28.761, SC 2013.28.793. Description The sagitta outline is somewhat rectangular (sensu Smale et al. 1995) in smaller specimens. Specimens larger than 5 mm show a marked distortion from the antero-dorsal to the posteroventral, which noticeably affects the overall shape. Furthermore, some of the larger specimens may show a hypertrophical development of the posteroventral margin, and there may also be an expansion of the antero-dorsal area. The margins are typically smooth. The inner face is somewhat convex and characterized by a very large, prominent heterosulcoid-type sulcus. The height of the cauda is slightly over 20% of the height of the ostium, and the cauda has a horizontal and downturned component. The outer face is not as convex as the inner face. Remarks Ontogenetic variation is apparent in our A. distortus otolith sample. For example, the ostium on juvenile specimens is much smaller in height, and the ventral margin of the sulcus has no expansion compared to adult specimens, where the ostium extends from near the antero-dorsal margin well down into the ventral field and is largest at the posterior portion. The ventral margin of the adult ostium curves distinctly upward toward the anterior margin and is subparallel to the anteroventral margin in larger specimens, and the posteroventral portion extends underneath the cauda. There are significant ontogenetic changes in the cauda, with the horizontal portion being significantly greater in length on smaller specimens compared adult specimens. Additionally, the downturned portion may have a greater length on large specimens, exceeding approximately 10 mm (see also Nolf 2003: pl. 4 fig. 4). The outer face ranges from nearly flat on small specimens to slightly more convex in larger specimens, and there is also greater convexity in the posterior portion than in the anterior. With respect to species identification, there is typically a wide area between the posterior of the ostium and the downturned portion of the cauda in Aplodinotus distortus, which is noticeably wider than that on A. gemma (see below). Aplodinotus distortus lacks the inframedian tip on the posterior margin occurring on Sciaena? radians sagittae. Nolf (2003) named Aplodinotus distortus based on specimens from the Byram Formation (Oligocene, Rupelian) at the Keyes Iron and Metal locality near Vicksburg, Mississippi, USA. Specimens were recovered from other Byram Formation exposures in the Vicksburg vicinity, and otoliths were also obtained from the Rosefield Marl Beds of the Rosefield Formation (Oligocene, Rupelian) in Catahoula Parish, Louisiana (Stringer & Worley 2003). One of the current authors (GLS) has observed that specimens 10 mm in length are common in several of the Byram Formation localities in the Vicksburg, Mississippi area. Although only 18 specimens of Aplodinotus distortus were recovered (including one tentatively referred to the species) from the Catahoula Formation at Jones Branch (4.4% of the otolith sample), the taxon is more abundant than Sciaena? radians but much less common than S.? pseudoradians and A. gemma. Like S.? pseudoradians, S.? radians, and Aplodinotus gemma, A. distortus is widespread in the Gulf Coastal Plain and is known from many Oligocene formations in Louisiana and Mississippi (Nolf 2003, 2013; Stringer & Worley 2003; Worley 2004).