Preophidion cf. P. petropolis 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 : 198-199

Preophidion cf. P. petropolis Frizzell & Dante, 1965

Fig. 70 E–F

Preophidion petropolis Dante & Frizzell in Frizzell & Dante, 1965: 713–714 , pl. 86, figs 34, 39.

“genus aff. Sirembo ” petropolis – Nolf 1980: 137 ; 1985: 66.

“genus Sirembinorum” petropolis – Müller 1999: 124 .

“aff. Sitrembo ” petropolis – Nolf 2013: 66 , pl. 128.

Material examined

UNITED STATES OF AMERICA – Alabama • 3 otoliths; MSC 7303.3, MSC 35076.1, MSC 39056.

Description

Sagittae oblong to elliptic in shape (sensu Smale et al. 1995), biconvex. Sagittae elongated with height/ length ratios approximately 55%. Greatest length of adult specimens around 3.5 mm. Margins primarily smooth. Anterior margin bluntly pointed; anterodorsal margin long, arched. Dorsal margin short, slightly arched. Posterodorsal margin very slightly arched, longer than anterodorsal margin. Posterior margin tapered, pointed. Ventral margin evenly and broadly rounded. Inner face smooth, convex, with lightly impressed, distinct sulcus. Sulcus divided, completely enclosed, marked by incised lines. Length of ostium noticeably shorter than cauda. Anterior end of ostium sharply pointed, almost touches anterodorsal margin. Ostium filled with colliculum, not excavated. Slight ventral constriction of ostium near junction (incised line) with cauda. Cauda also slightly wider than ostium. Ventral margin of cauda more rounded than corresponding ventral margin of ostium. Cauda not excavated, filled with colliculum. Posterior end of cauda rounded, somewhat tapered, separated from posterior margin by distinct, narrow border. Cristae lacking or very weakly developed. Ventral furrow usually absent. Outer face convex, with dorsal portion more strongly convex. Outer face undulating to strongly sculptured.

Remarks

The most conspicuous differences between Preophidion petropolis and P. meyeri , a very abundant taxon in the Alabama Claiborne Group, is the dorsal margin and the intersection of the ostium and cauda. The dorsal margin of P. petropolis tends to be more broadly rounded, and the dorsal domes are not as high or prominent. The anterodorsal dome of P. meyeri is typically more pronounced, which affects the dorsal outline. The intersection of the cauda and ostium of P. petropolis is sharply inclined toward the anterior (approximately 45-degrees) and extends significantly over the posterior of the ostium. In contrast, the intersection on P. meyeri is not nearly as inclined (less than half as much as Preophidion petropolis ).

Frizzell & Dante (1965) noted abundant P. petropolis from the Claibornian of Texas, especially at the Stone City Locality, but they did not list the species from Alabama. However, those authors referenced a collection of otoliths from the Gosport Sand at site ACl- 4 in Alabama that contained P. petropolis . Frizzell & Dante (1965) stated that this species was not found in the Lisbon Formation in Alabama, but we do not know how extensive their collections were. Although we could not corroborate the presence of P. petropolis in the Gosport Sand, our sample shows that, while not abundant, this species does occur in the Lisbon Formation in Alabama.

Nolf (1980, 1985, 2013) assigned P. petropolis to the ophidiid genus Sirembo , and the otoliths of these taxa exhibit some similarities. Our specimens compare well to fossil Preophidion as described by Frizzell & Dante (1965), Stinton (1977), Schwarzhans & Bratishko (2011), and Schwarzhans (2012). We retain the specimens within Preophidion , but a larger sample size is needed to strengthen our specific identification.

Stratigraphic and geographic range in Alabama

Specimens were recovered from the “upper” Lisbon Formation at sites ACh-8 and ACl-16. 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.