Symmetrosulcus dockeryi, Lin & Nolf & Steurbaut, 2022

Lin, Chien-Hsiang & Nolf, Dirk, 2022, Middle and late Eocene fish otoliths from the eastern and southern USA, European Journal of Taxonomy 814, pp. 1-122 : 55-56

Symmetrosulcus dockeryi sp. nov.

urn:lsid:zoobank.org:act:124FFDA6-FA7C-442E-AC9E-88BE08F77445

Fig. 18G–K

Diagnosis

OL/OH = 1.47–1.57, OsL/CaL = 1.43–1.73. Elliptic otoliths with angled posterior rim. Ventral rim deepest in the middle. Sulcus wide, oblong, but narrow. Ostium longer than cauda, each filled with a colliculum.

Etymology

The species is named in honor of David T. Dockery III (Mississippi Bureau of Geology) who provided major support during our field work.

Material examined

Holotype UNITED STATES OF AMERICA • Left otolith; Texas, Wall Farm 1; Weches Formation ; Fig. 18G ; IRSNB P 10090 .

Paratypes UNITED STATES OF AMERICA • 191 otoliths of which four are figured: Fig. 18H–K ; same collection data as for holotpye; IRSNB P 10091–10094 .

Type locality and horizon

United States of America, Wall Farm 1 (Texas), Weches Formation.

Dimensions of the holotype

Length = 3.16 mm; height = 2.11 mm; thickness = 0.93 mm.

Description

This species is characterized by elliptical otoliths with blunt, but well-marked antero- and postero-dorsal angles. The rim between those two angles is almost horizontal, but may be very slightly undulated in the smaller individuals ( Fig. 18I ). The posterior portion of the otoliths forms a tapering triangle. The ventral rim is smoothly curved with its deepest part in the middle of the otolith, providing it a regular rounded appearance. The anterior part of the otolith is slightly oblique and largely blunt at its lower, most prominent part. All the margins are smooth. The otoliths are moderately thick, with both the inner and outer faces convex. The thickness may be slightly more considerable near the posterior end, which is the case in the holotype ( Fig. 18G ). A straight sulcus occupies nearly the entire length of the inner face and is located in the central zone, but does not open to the margins of the otolith. There is a clear division into ostial and caudal parts, each fully filled by a colliculum. The cauda is about twice as long as the ostium. The cristae are clearly marked, but not ridge-like. They are almost horizontal, but the crista inferior may be slightly constricted at the collum, which is well visible in the holotype ( Fig. 18G ).

Comparison

The otoliths of this species can be distinguished from the co-occurring related species, S. meyeri ( Koken, 1888) , S. stintoni (Dante & Frizzell, 1965) , “ N. ” rotundus ( Müller, 1999), and “ N. ” virginicus Müller, 1999, by the combination of the following features: a more rectangular outline, a nearly flat dorsal rim, a more vertical anterior rim, a less extended posterior rim, and a dorsal area of similar width as the ventral one. See below for a detailed discussion on other ophidiid otoliths.

Stratigraphic and geographic distribution

Lutetian: Weches Formation, Texas; “lower” Lisbon Formation, Alabama. Bartonian: Cook Mountain Formation, Mississippi.

Figures

Fig. 18. Fish otoliths from the US middle and upper Eocene.A–F. Symmetrosulcus meyeri (Koken, 1888). A–C. Yazoo Clay, Copenhagen, Louisiana (IRSNB P10084–10086). D–F. “Stone City beds”, Stone City Bluff, Brazos River, sample 2 from bed P, Texas (IRSNB P 10087–10089). G–K. Symmetrosulcus dockeryi sp. nov., Weches F., Wall Farm 1, Texas. G. Holotype (IRSNB P 10090). H–K. Paratypes (IRSNB P 10091–10094). L–M. “Neobythites” virginicus Müller, 1999, Piney Point F., Pamunkey River, 1 km E of Eanes property, Virginia (IRSNB P 10095–10096). N–P. Symmetrosulcus stintoni (Dante & Frizzell, 1965), “Stone City beds”, Stone City Bluff, Brazos River, sample 2 from bed P, Texas (IRSNB P 10097–10099). 1 = ventral view; 2 = inner view. Scale bars = 1 mm.