Diretmus, Johnson, 1864

Ebersole, Jun A., Cicimurri, David J. & Stringer, Gary L., 2019, Taxonomy and biostratigraphy of the elasmobranchs and bony fishes (Chondrichthyes and Osteichthyes) of the lower-to-middle Eocene (Ypresian to Bartonian) Claiborne Group in Alabama, USA, including an analysis of otoliths, European Journal of Taxonomy 585, pp. 1-274 : 195

Diretmus ? cf. D. serratus ( Müller, 1999)

Fig. 70 A–B

“genus Caproidarum ” serratus Müller, 1999: 130 , pl. 29, figs 18–21.

“ Diretmida ” serrata – Nolf 2013: 78, pl. 163.

Material examined

UNITED STATES OF AMERICA – Alabama • 1 otolith; MSC 42212 .

Description

Sagitta tall (i.e., height twice its length), dorsal and ventral both tapered. Margins appear fairly smooth; evidence of several prominent lobes dorsally. Anterior margin short, nearly vertical, characterized by opening of sulcus. Anterodorsal margin fairly steep, outwardly curved, indications of at least three prominent lobes. Dorsal margin pointed, short. Posterodorsal margin quite steep, incurved. Posterior short, slightly rounded, nearly vertical. Steep posteroventral margin slants from posterior to ventral. Ventral margin short with rounded point. Anteroventral margin steep, relatively straight to slightly outwardly curved. Prominent sulcus extends across nearly 90% of otolith length.

Remarks

Only one ablated sagitta was recovered, but salient characteristics are indicative of to Diretmus cf. D. serratus ( Müller, 1999) . The specimen is quite unique in its shape, being uncommonly tall for the otoliths of the Gulf Coast Paleogene (sensu Smale et al. 1995). Details of the sulcus are not preserved due to erosion. However, D. serratus otoliths from Claibornian strata in Texas indicate that the ostium is very small, and the cauda is approximately four times longer than the ostium. The cauda is fairly wide, and its margins are almost parallel. The posterior of the cauda is rounded. There is a depressed area well above the cauda. The other face is slightly convex and highly sculptured.

Müller (1999) first described this species from the middle Eocene Piney Point Formation (Pamunkey Group) in Hanover County, Virginia. The taxon was originally assigned to the Caproidae , but Nolf (2013) placed it within the Diretmidae . In all known occurrences (Alabama, Texas, Virginia), the species is quite rare within vertebrate assemblages.

Stratigraphic and geographic range in Alabama

Only one specimen of this species was found in the study. It was derived from the “upper” Lisbon Formation at site ACh-7. Bartonian, zones NP16 and NP17.

Figures

Fig. 70. Claiborne Group, “upper” Lisbon Formation, otoliths. A–B. Diretmus? cf. D. serratus (Müller, 1999), MSC 42212. A. Inner face (left sagitta). B. Anterior view. — C–D. Preophidion meyeri (Koken, 1888), MSC 39055. C. Inner face (right sagitta). D. Dorsal view. — E–F. Preophidion cf. P. petropolis Frizzell & Dante, 1965, MSC 42193. E. Inner face (right sagitta). F. Dorsal view. — G–H. Signata stenzeli Frizzell & Dante, 1965, MSC 39051. G. Inner face (left sagitta). H. Dorsal view. — I–J. Signata nicoli Frizzell & Dante, 1965, MSC 39046. I. Inner face (left sagitta). J. Dorsal view. — K–L. Hoplobrotula melrosensis (Frizzell & Dante, 1965), MSC 37059.3. K. Inner face (right sagitta). L. Dorsal view. — M–N. Lepophidium? mucronata (Koken, 1888), MSC 39054. M. Inner face (left sagitta). N. Dorsal view. — O–P. Gobiidae Cuvier, 1816, indet. MSC 39045. O. Inner face (left sagitta). P. Dorsal view. — Q–R. Bothidae Smitt, 1892, indet. MSC 42235. Q. Inner face (right sagitta). R. Dorsal view. Scale bars: A–P= 2 mm; Q–R =1 mm.