Symmetrosulcus virginicus, Lin & Steurbaut & Nolf, 2024

Lin, Chien-Hsiang, Steurbaut, Etienne & Nolf, Dirk, 2024, Early Eocene fish otoliths from the eastern and southern USA, European Journal of Taxonomy 935, pp. 203-240 : 219-220

Symmetrosulcus virginicus sp. nov.

urn:lsid:zoobank.org:act:72E254E4-1823-4F6B-9E38-3C7F45389634

Fig. 7C–F

Diagnosis

OL/OH = 1.7–1.8, OsL/CaL = 1.0–1.4. Elliptic otoliths with angled posterior rim. Concave postero-ventral rim. Dorsal and ventral rims gently curved. Anterior rim blunt. Sulcus very wide and elongate. Ostium slightly longer than cauda, similar width, each filled with colliculum.

Etymology

‘ Virginicus , a, um ’ = ‘from Virginia’. The name alludes to the state, where the holotype was collected.

Type material examined

Holotype UNITED STATES OF AMERICA • Left otolith; Virginia, Pamunkey River, Hanovertown , Potapaco Member ; Fig. 7C ; IRSNB P 10740 .

Paratypes (51 in total) United States of America • 44 otoliths of which three are figured: Fig. 7D–F ; same collection data as for holotype; IRSNB P 10741 to P 10743 • 3 otoliths; Alabama, Hatchetigbee Bluff, Hatchetigbee Formation; IRSNB • 1 otolith; Maryland, Loyola Retreat House , N of Popes Creek, Woodstock Member; IRSNB • 3 otoliths; Maryland, Piscataway Creek , Thrift Road ravine, Potapaco Member; IRSNB .

Type locality and horizon

United States of America, Pamunkey River, Hanovertown (Virginia), Potapaco Member.

Dimensions of the holotype

Length = 3.41 mm; height = 1.96 mm; thickness = 1.38 mm.

Description

The otoliths of this new species are elliptical in shape, with a blunt anterior rim and a well-marked posterior angle. The dorsal and ventral rims are gently curved, and their deepest part is in the middle of the otoliths, giving them a regular, rounded appearance.All margins are smooth, and the otoliths are considerably thick, with both the inner and outer faces being convex ( Fig. 7C 1 ). A straight, wide, and well-divided sulcus occupies nearly the entire length of the inner face and is located in the central zone of the otoliths. The ostial and caudal parts are each fully filled by a colliculum. The ostium reaches the anterior margin, while the cauda extends backward to the origin of the posterior angle but does not reach the posterior margin. The cauda is slightly shorter than the ostium. The ventral area is of similar size as the dorsal one.

Remarks

The general shape of the otoltihs and the caudal type of this new species are similar to those of Symmetrosulcus meyeri ( Koken, 1888) (see Lin & Nolf 2022: fig. 18a–f), whereas the thickness of the otoliths is similar to that of the otoliths of Preophidion , such as P. elevatus ( Koken, 1888) and P. granus ( Müller, 1999) . However, the otoliths of the new species exhibit a concavity on the postero-ventral rim, and its sulcus is much wider than that of S. meyeri . On the other hand, the cauda of the new species does not bend as strongly as that of Preophidion . The sulcus of the new species suggests that it is more similar to Symmetrosulcus than to Preophidion .

Stratigraphic and geographic distribution

Ypresian: Hatchetigbee Formation, Alabama; Potapaco Member, Virginia and Maryland; Woodstock Member, Maryland.

Figures

Fig. 7. Fish otoliths from the US lower Eocene formations. A. Glyptophidium polli (Casier, 1946), Pamunkey River, Hanovertown, Potapaco Member, Virginia (IRSNB P 10738). B. “Neobythites” constrictus Stinton, 1977, Rappahannock River, Potapaco Member, Virginia (IRSNB P 10739). C–F. Symmetrosulcus virginicus sp. nov., Pamunkey River, Hanovertown, Potapaco Member, Virginia. C. Holotype (IRSNB P 10740). D–F. Paratypes (IRSNB P 10741 to P 10743). G. “Neobythites” pamunkeyensis sp. nov., Pamunkey River, Hanovertown, Potapaco Member, Virginia, holotype (IRSNB P 10744). 1 = ventral view; 2 = inner view. Scale bars = 1 mm.

Fig. 1. Maps showing the sampling sites on the US Gulf Coastal Plain (Texas, Mississippi, and Alabama) and Atlantic Coastal Plain (A = Virginia and Maryland). 1. Ridge Creek. 2–4. Taylor’s Branch of Two Mile Creek, samples 1–3. 5. Meridian, Gallagher Creek. 6. Meridian, Red Hot Truck Stop. 7. Hatchetigbee Bluff. 8. Cave Branch. 9. Elba Dam on Pea River. 10. Ozark. 11. Pamunkey River, E of Hanover School for boys. 12. Pamunkey River, Hanovertown. 13. Pamunkey River, 1 km W of Hunters Club. 14. Pamunkey River, Hunters Club. 15. Rappahannock River. 16. Loyola Retreat House, N of Popes Creek. 17. Popes Creek, South. 18. Piscataway Creek, Thrift Road ravine.