Ampheristus brevicaudatus, 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 : 217-219

Ampheristus brevicaudatus sp. nov.

urn:lsid:zoobank.org:act:4ACB919D-6809-44FF-AE33-560D58E9276B

Fig. 6D–G

Diagnosis

OL/OH = 1.8–2.1, OsL/CaL = 2.0–3.1. Otoliths with notable pointed or protruding posterior rim. Sulcus straight, elongate, well-divided into ostium and cauda, both filled with colliculum. Cauda short, oblong, ventrally oriented posteriorly.

Etymology

‘ Brevicaudatus, a, um ’ = ‘having a short cauda’. Refers to the very small and short cauda.

Type material examined

Holotype UNITED STATES OF AMERICA • Left otolith; Virginia, Rappahannock River, Potapaco Member; Fig. 6D ; IRSNB P 10734 .

Paratypes (14 in total) UNITED STATES OF AMERICA • 12 otoliths of which three are figured: Fig. 6E–G ; same collection data as for holotype; IRSNB P 10735 to P 10737 • 1 otolith; Alabama, Cave Branch, Bashi Formation; IRSNB • 1 otolith; Maryland, Loyola Retreat House, N of Popes Creek, Woodstock Member; IRSNB .

Type locality and horizon

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

Dimensions of the holotype

Length = 3.85 mm; height = 1.84 mm; thickness = 0.79 mm.

Description

This species has fusiform otoliths with a postero-ventral angle that is extended. While the holotype has a pointed angle ( Fig. 6D ), it is typically blunt in other specimens (probably a result of abrasion). The margins are smooth, but may be slightly lobated in some specimens along the anterior and postero-dorsal rims ( Fig. 6F ). The antero-dorsal rim is slightly elevated, but not protruding dorsally, while the anterior rim forms a large, obtuse rostrum. The inner face is slightly convex; the outer face is concave posteriorly, but may be slightly convex anteriorly. The sulcus is well-divided into an elongate ostium and a very short, much narrower cauda that points downwards. Both the ostium and cauda are filled with a colliculum each. The ventral area is of similar size to the dorsal area. There is a shallow, elongate dorsal depression above the crista superior.

Remarks

Otoliths of Ampheristus are mainly known from Paleogene European deposits ( Nolf 2013), with two species from the Lutetian of New Zealand ( Schwarzhans 2019). The first record of the genus from the New World region is Ampheristus americanus Schwarzhans & Stringer, 2020 , a recently described Maastrichtian–Danian species from the southern USA ( Schwarzhans & Stringer 2020; Stringer & Schwarzhans 2021). The cauda of A. brevicaudatus sp. nov. is much shorter than that of A. americanus . The posterior rim of A. brevicaudatus also appears to be more pointed than the truncated rim of A. americanus . The occurrences of the new species and A. americanus indicate a much wider geographic distribution and longer stratigraphic range of Ampheristus .

Stratigraphic and geographic distribution

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

Figures

Fig. 6. Fish otoliths from the US lower Eocene formations. A. Bauzaia gibbosa sp. nov., Loyola Retreat House, N of Popes Creek, Woodstock M., Maryland (IRSNB P 10731). B–C. Bauzaia mucronata (Koken, 1891), Taylor’s Branch of Two Mile Creek, Reklaw Fm., Texas (IRSNB P 10732, P 10733). D–G. Ampheristus brevicaudatus sp. nov., Rappahannock River, Potapaco Member, Virginia. D. Holotype (IRSNB P 10734). E–G. Paratypes (IRSNB P 10735 to P 10737). 1 = ventral view; 2 = inner view. Scale bars = 1 mm.