Gen. et sp., Cuvier, 1825

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 : 154-155

Gen. et sp. indet.

Fig. 57 M–BB

Lepisosteidae – Thurmond & Jones 1981: 84.

Lepisosteus sp. – Clayton et al. 2013: 65, fig. 6a. — Maisch et al. 2016: 7, fig. 2, 3–4.

Material examined

UNITED STATES OF AMERICA – Alabama • 36 isolated teeth; Claiborne Group ; ALMNH PV 1989.2.4, ALMNH PV1989.4.114.5, ALMNH PV1989.4.118.3, ALMNH PV1989.4.131.2, ALMNH PV1989.4.190, ALMNH PV1989.4.37.1 (4 specimens), ALMNH PV1989.4.37.2 (2 specimens), ALMNH PV1989.4.70, MSC 188.188 , MSC 2156 , MSC 2404.1 – 11 , MSC 33846, MSC 37306, MSC 37461, MSC 37473.1 – 3 , MSC 37476, MSC 38514.1 – 2 , NJSM 24038 , WSU 25 .

Description

Teeth, scales, and vertebrae identified in our sample. Teeth average 4.0 mm in overall height, 1.0 mm in greatest width. Teeth cylindrical with apical carinae. Lateral edges of tooth ornamented with low parallel ridges. Ridges strongest basally, fining apically. Crown apex translucent. Lateral edges of tooth base taper apically; lateral edges of crown apex more tapered. Some teeth can have a slight medial bend.

Scales of two morphologies, including large, thickened, with heavy ganoin ornamentation; others small, thin, smooth. Scales generally rhomboidal; thickest medially (up to 0.5 mm); inner surface convex, smooth; lateral edges sharp to rounded. Concentric growth line visible on some specimens.

Vertebrae opisthocoelous, with shallow concave posterior articular surface, slightly convex anterior surface; both surfaces with circular outline. Neural and hemal arches not preserved, but broken spine bases visible.

Remarks

Fossil elements belonging to Lepisosteidae were first reported from the Eocene of Alabama by Thurmond & Jones (1981), and later Clayton et al. (2013) and Maisch et al. (2016) assigned isolated scales from the Lisbon Formation to Lepisosteus sp. Two scale morphologies occur in Claibornian strata, including thin and smooth as well as thin and ornamented. Large, thickened ganoid scales have traditionally been assigned to Atractosteus , whereas smaller, thinner, unornamented scales have been identified as Lepisosteus (see Wiley 1976; Maisch et al. 2016). However, in his study of extant gars, Grande (2010) noted that the degree of ornamentation on the scales of Atractosteus varies from heavy to absent. Furthermore, ornamentation is more prevalent on the scales in certain areas on the body (heaviest in the trunk and prepelvic area, for example) and is more prominent on larger (older) individuals (i.e., ontogenetic development, with scale ornamentation in the caudal region being the last to form). Furthermore, Grande (2010) recognized four Eocene genera within the Lepisosteidae , Atractosteus, Cuneatus , Lepisosteus , and Masillosteus . Although the scales of Lepisosteus lack ganoid ornamentation, it can be present on the scales of Atractosteus, Cuneatus , and Masillosteus . Thus, all four genera can have unornamented scales, depending on the age of the gar and/or location of the scale on the body ( Grande 2010), and the presence or absence of ganoin ornamentation on scales is not a taxonomically useful characteristic.

Grande (2010) also demonstrated that centrum length of a vertebra can vary depending on the location in the spinal column, and the morphology of these gar vertebrae overlaps within the various genera. Although size differences can be observed among the vertebrae in our sample, these differences could be attributed to ontogeny. Furthermore, generic identification of isolated gar teeth is also problematical, as Wiley (1976) and Grande (2010) have shown that there is little morphological difference between the various taxa, and gars generally have multiple rows of teeth of varying size. Thus, according to Grande (2010), specific cranial elements or nearly complete articulated gar specimens are needed for generic and specific assignments, since isolated scales, teeth, and vertebrae cannot be confidently identified beyond the familial level.

Stratigraphic and geographic range in Alabama

The specimens in our sample were collected from the contact of the Tallahatta and Lisbon formations at site ACh-14, the basal Lisbon Formation at site ACov-11, the basal Gosport Sand at site ACl-4, and the Gosport Sand at site ACh-21. Upper Ypresian to middle Bartonian, zones NP14 to NP17.

Figures

Fig. 57. Pycnodus sp., teeth and Lepisosteidae elements. A–L. Pycnodus sp. A–C. MSC 35773.1, tooth, lower Tallahatta Formation. A. Oral view. B. Profile view. C. Aboral view. D–F. MSC 35773.2, tooth, lower Tallahatta Formation. D. Oral view. E. Profile view. F. Aboral view. G–I. MSC 37185, tooth, Tallahatta/Lisbon formation contact zone, courtesy of T. Prescott Atkinson. G. Oral view. H. Profile view. I. Aboral view. J–L. MSC 37912.1, tooth, basal Lisbon Formation. J. Oral view. K. Profile view. L. Aboral view. — M–BB. Lepisosteidae Cuvier, 1825. M–N. ALMNH PV1989.4.70, scale, Gosport Sand. M. External view. N. Internal view. O–P. ALMNH PV1989.4.37.2.1, scale, Gosport Sand. O. External view. P. Internal view. Q–R. ALMNH PV1989.4.37.2.2, scale, Gosport Sand. Q. External view. R. Internal view. S–T. MSC 37306, scale, basal Lisbon Formation. S. External view. T. Internal view. U–V. MSC 37473.1, tooth, basal Gosport Sand. U. Lateral view. V. Basal view. W–Y. ALMNH PV1989.2.4, vertebra, Gosport Sand. W. Anterior view. X. Left lateral view. Y. Posterior view. Z– BB. ALMNH 1898.4.190, vertebra, Gosport Sand. Z. Anterior view. AA. Left lateral view. BB. Posterior view. Scale bars for A–L=2 mm. Scale bars: M–T, W–BB =1 cm; U =5 mm.