Syacium undetermined

Syacium sp. Fig. 25G–H Material examined UNITED STATES OF AMERICA – Mississippi • 3 sagittae; Catahoula Formation; MMNS VP-12074, GLS otolith comparative collection (2 specimens). Description The sagittae have a primarily square outline (sensu Smale et al. 1995). The margins are generally smooth but can be variable and irregular. The inner face is slightly convex and smooth (Fig. 25H). A highly specialized, fusiform sulcus slants downward from the posterodorsal margin to almost the anteroventral margin (Fig. 25G). The sulcus is widest just behind its midline but is narrower at the anterior and posterior ends. Although the sulcus extends across approximately 75% of the inner face, it is narrow and represents roughly 20% of the height. The sulcus is divided into ostial and caudal areas. The ostium is located near the lower portion of the anterior and anteroventral margins but does not reach the margins. The ostium is tapered and almost pointed at the anterior end. The cauda is longer and wider than the ostium, and the anterior of the cauda is tapered, whereas the center portion is enlarged. The cauda is excavated slightly deeper than the ostium. The ostium and cauda are conspicuously connected or fused, and the structure is filled with colliculum. A marked circumsulcal depression extends from above the ostium, around the cauda, and ends below the ostium. The circumsulcal depression forms an elevated flattened area for the fusiform sulcus. A ventral furrow is not present. The outer face is fairly flat on the dorsal and ventral areas, but is slightly convex in the center. Remarks The Syacium sp. otoliths from the Catahoula Formation are very similar to the Syacium sp. sagittae from the Rupelian Glendon Limestone Member of the Byram Formation of Alabama (Ebersole et al. 2021). This genus appears to be rare in Paleogene strata across the Gulf and Atlantic coastal plains of the USA, but it is somewhat more common (although still rare) during the Neogene (Stringer 1992; Nolf & Stringer 2003; Nolf 2013; Stringer et al. 2017; Stringer & Bell 2018; Ebersole et al. 2019; Stringer & Shannon 2019; Stringer & Hulbert 2020).