Hoplobrotula melrosensis ( Frizzell & Dante, 1965 )

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 : 200-201

Hoplobrotula melrosensis ( Frizzell & Dante, 1965)

Fig. 70 K–L

Bauzaia melrosensis Dante & Frizzell in Frizzell & Dante, 1965 : pl. 86, figs 7, 9. Hoplobrotula melrosensis – Nolf 1980: 103 , pl. 20, fig. 6; 1985: 66; 2013: 67, pl. 132.

Material examined

UNITED STATES OF AMERICA – Alabama • 1 otolith; MSC 37059.3 .

Description

Sagittae primarily oval in shape but with prominent anterodorsal dome. Height/length ratio is approximately 55%, exclusive of anterodorsal dome. Margins mainly smooth. Anterior margin fairly steep, somewhat rounded. Anterodorsal slope quite steep, depending upon development of anterodorsal dome. Dorsal margin almost straight to slightly inclined toward posterior. Posterodorsal slope gently inclined. Posterior rounded but tapered. Ventral margin broadly rounded, but posteroventral slope slightly steeper. Smooth inner face slightly convex. Sulcus fairly narrow, long (approximately 90% of the otolith’s length), clearly divided into ostium and cauda. Sulcus not deeply excavated, edges slightly incised. Sulcus extending essentially from anterior margin to near the posterior margin (distinct space between posterior of sulcus and posterior margin). Dorsal margin of sulcus essentially straight, whereas ventral margin slightly inflated toward ventral in the ostium, constricted at ostium/cauda intersection. Ostium approximately three times longer than cauda. Cauda approximately oval in shape, much smaller in length than ostium. Cristae not developed, no depressed area observed. Ventral furrow weakly developed in anteroventral and mid-ventral. Outer face slightly and irregularly concave.

Remarks

This species is very common in the Claibornian of Texas, especially at the Stone City locality on the Brazos River near Bryan, Texas ( Frizzell & Dante 1965) and the Cane River site near Natchitoches, Louisiana ( Stringer & Breard 1997; reported as Hoplobrotula sp.). An excellent figure of the species is found in Nolf (1980: pl. 20, 6a–6b). The species has been reported as being strongly facies controlled, which may account for its rarity in the Claibornian strata of Alabama. In the original description of this species, Frizzell & Dante (1965) noted that it was common at some levels at the classic middle Eocene (Claiborne Group) Stone City Bluffs on the Brazos River, Burleson County, Texas, USA, but was replaced by an ecological analogue in other levels, typically of varying composition. The complexity of the Stone City Bluffs with cyclic sedimentation, rhythmic alteration of varying grain sizes, and storm deposits has been detailed in Flis et al. (2017). Ophidiids are strictly marine ( Nelson et al. 2016), variations in environmental conditions will affect their distribution. Furthermore, Snyder & Burgess (2016) have pointed out that many of the cusk-eels (ophidiids) are distributed in the marine waters of Florida according to depth preferences. These depth preferences serve to sort out the ophidiids over the continental shelf and the slope edge, which often correspond to different sediment types or facies.

Stratigraphic and geographic range in Alabama

The specimen examined came from the “upper” Lisbon Formation at Locality 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.