Paralbula, Blake, 1940

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 : 158-159

Paralbula aff. P. marylandica Blake, 1940

Fig. 59 A–O

Paralbula marylandica Blake, 1940: 206 , figs 1–2.

Albula sp. – Maisch et al. 2016 (partim): fig. 2.7–8 (non 5–6).

Material examined

UNITED STATES OF AMERICA – Alabama • 69 isolated teeth; Claiborne Group ; MSC 35781.1 – 17 , MSC 37263.1 – 4 , MSC 37911.1 – 26 , MSC 37913.2 – 4 , MSC 38292.1 , SC 2012.47.124 (10 specimens), WSU 35 , WSU CC 561 (5 specimens), WSU CC 563 (2 specimens) .

Description

Teeth up to 2.0 mm in diameter, 0.5 mm in crown height. Crown with circular occlusal outline, uniformly convex in profile. Thick cingulum at crown base of some teeth. Crown enameloid extends to tooth base on most specimens, but not on all. Fine granular to wrinkled ornament often on occlusal surface of unworn teeth. Teeth with thickened, flat base; shallow, centrally located, circular pulp cavity.

Remarks

Estes (1969) and Schein et al. (2011) recognized three species of Paralbula having an Eocene range, including P. casei Estes, 1969 , P. marylandica Blake, 1940 , and P. stromeri ( Weiler, 1929) . Although each of these species were described from partial or complete tooth plates, Estes (1969) noted that the teeth of P. casei have a much more pronounced granular ornamentation, which is often arranged in lateral ridges that originate at the apex of the crown and extend to the crown base. We have also observed on complete tooth plates from the Paleocene and Cretaceous of Mississippi (MMNS 5367, MMNS 6885, MMNS 8076) that the granular ornamentation and ridges are visible even on worn or abraded teeth. Although the teeth of P. marylandica can also have a granular ornamentation, it is often much less apparent than that on P. casei , the ornamentation is not organized into radiating ridges, and many of the teeth have smooth enameloid (see Blake 1940; Estes 1969). Similar to P. marylandica , the teeth of P. stromeri have a smooth crown that lacks ornamentation (see Weiler 1929; Estes 1969). Another species, Paralbula salvani ( Arambourg 1952) , has a similar granular ornamentation to that on the teeth of P. casei , but this taxon is known only by the type specimen, which was derived from Paleocene deposits in Morocco ( Estes 1969; Schein et al. 2011).

The Paralbula teeth within our sample have either a smooth crown or exhibit granular ornamentation, indicating that the isolated teeth do not belong to P. casei or P. salvani but instead represent P. marylandica or P. stromeri . Although the teeth of the latter two taxa are similar, we tentatively assign the specimens in our sample to P. marylandica because this is the only smooth-crowned species that has been described from the Eocene in North America (see Blake 1940; Estes 1969; Weems 1999; Schein et al. 2011). Paralbula stromeri , on the other hand, appears to have had a limited range that is currently restricted to the upper Eocene of Egypt ( Weiler 1929; Estes 1969).

These Claiborne Paralbula teeth were differentiated from those of the morphologically similar Egertonia isodonta and Phyllodus toliapicus by the presence of distinct granular crown ornamentation on some specimens, and a medial pulp cavity on the basal surface. Furthermore, the basibrachial plates of Paralbula marylandica consist of teeth that are irregularly stacked (as opposed to columns of regularly stacked teeth on Egertonia and Phyllodus ) and they lack the ovoid median teeth present on the tooth plates of Phyllodus toliapicus .

Stratigraphic and geographic range in Alabama

The specimens in our sample were collected from the lower Tallahatta Formation at site ADl-1, and the basal Lisbon Formation at site ACov-11. Upper Ypresian to Lutetian, zones NP14 to NP15.

Figures

Fig. 59. Paralbula aff. P. marylandica Blake, 1940 and Phyllodus toliapicus Agassiz, 1844, teeth. A–O. Paralbula aff. P. marylandica. A–C. MSC 35781.1, lower Tallahatta Formation. A. Oral view. B. Profile view. C. Aboral view. D–F. MSC 35781.2, lower Tallahatta Formation. D. Oral view. E. Profile view. F. Aboral view. G–I. MSC 37911.2, basal Lisbon Formation. G. Oral view. H. Profile view. I. Aboral view. J–L. MSC 37263.2, basal Lisbon Formation. J. Oral view. K. Profile view. L. Aboral view. M–O. MSC 37911.3, basal Lisbon Formation. M. Oral view. N. Profile view. O. Aboral view. — P–AA. Phyllodus toliapicus. P–S. MSC 35772.3, lower Tallahatta Formation. P. Oral view. Q. Labial view. R. Profile view. S. Aboral view. T–W. MSC 35772.2, lower Tallahatta Formation. T. Oral view. U. Labial view. V. Profile view. W. Aboral view. X–AA. MSC 35772.1, lower Tallahatta Formation. X. Oral view. Y. Labial view. Z. Profile view. AA. Aboral view. Scale bars: A–O =1 mm; P–AA=5 mm.