Astroscopus compactus, 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 : 74-75

Astroscopus compactus sp. nov.

urn:lsid:zoobank.org:act:D6BFE465-59DD-4A7A-8965-9EED7217997D

Fig. 25C–G

Diagnosis

OL/OH = 1.55–1.67. Fusiform otoliths with blunt anterior and extended posterior rims. Sulcus narrow, long and divided into ostium and cauda. Ostium gently curving upwards and cauda curving ventrally at posterior.

Etymology

From the Latin adjective ‘ compactus , -a, -um ’, meaning ‘compact, massive’ and alluding to the thick and robust aspect of the otoliths.

Material examined

Holotype UNITED STATES OF AMERICA • Left otolith; Alabama, Little Stave Creek; Gosport Sand ; Fig. 25C ; IRSNB P 10148 .

Paratypes UNITED STATES OF AMERICA • 10 otoliths, of which two are figured: Fig. 25D–E ; Mississippi, Newton, NE exit off Interstate 20; Poterchito Member ; IRSNB P 10149 – 10150 • 17 otoliths, of which two are figured: Fig. 25F–G ; Alabama, Evansboro (SE of town); “upper” Lisbon Formation ; IRSNB P 10151–10152 • 1 otolith; Mississippi, Quitman, Archusa Water Park ; Archusa Marl Member .

Type locality and horizon

United States of America, Little Stave Creek (Alabama), Gosport Sand.

Dimensions of the holotype

Length = 2.23 mm; height = 1.41 mm; thickness = 0.67 mm.

Description

This species is characterized by robust, fusiform otoliths. Both the anterior and posterior rims are tapering but the posterior rim is more extended than the anterior one. The tip of the posterior rim varies; it may show none ( Fig. 25F ), one ( Fig. 25C ) or two undulations ( Fig. 25G ). The dorsal and ventral rims are of equal length and markedly curved, with the highest part of the otolith in the middle. The otoliths are thick; they have a strongly convex inner face and an outer face that is nearly flat in the antero-posterior direction, but convex dorso-ventrally. The extended part of the posterior rim is the thinnest zone of the otolith. The sulcus is shallow, narrow and located very slightly at the base of the dorsal part of the otolith. There is no division into ostium and cauda by the constriction of the cristae, but the entire sulcus is rather undulated, with a long transitional zone connecting the ostium and cauda. The ostium is filled with a long colliculum and is slightly curved upwards, with its highest part at the anterior end, which opens dorsally. The cauda is slightly bent downwards in ventral direction, and ends at the lowest level of the sulcus. The cristae are not very salient, but they are sufficiently marked to delimit the margins of the sulcus. The ventral area is wide and deeper than the height of the dorsal one.

Remarks

This new species is readily distinguished from the congeneric Astroscopus fusiformis ( Müller, 1999) (see below) by its more rounded appearance and more considerable thickness profile. Astroscopus fusiformis is known from the Piney Point Formation of Virginia only, while A. compactus sp. nov. is found in the “upper” Lisbon Formation of Alabama and the Cook Mountain Formation of Mississippi.

Stratigraphic and geographic distribution

Bartonian: Cook Mountain Formation, Mississippi; “upper” Lisbon Formation, Alabama.

Figures

Fig. 25. Fish otoliths from the US middle and upper Eocene.A–B. “Trachinus” laevigatus (Koken, 1888). A. Moodys Branch F., Midway, Techeva Creek, Mississippi (IRSNB P 10146). B. “Stone City beds”, Rocky Branch,1.5 miles SW of Stone City Bluff, Texas (IRSNB P 10147). C–G. Astroscopus compactus sp. nov. C. Gosport Sand, Little Stave Creek, Mississippi, holotype (IRSNB P 10148).D–E. Potterchitto M., Newton, NE exit off Interstate 20, Mississippi, paratypes (IRSNB P 10149–10150). F–G. “Upper” Lisbon F., Evansboro (SE of town), Alabama, paratypes (IRSNB P 10151–10152). H–K. Astroscopus fusiformis (Müller, 1999), Piney Point F., Pamunkey River, 1 km E of Eanes property, bed A, Virginia (IRSNB P 10053–10156). 1 = ventral view; 2 = inner view. Scale bars = 1 mm.