Phyllodus toliapicus Agassiz 1844

Phyllodus toliapicus Agassiz, 1844

Fig. 59 P–AA

Phyllodus toliapicus Agassiz, 1844: 239, vol. 2, pl. 69a, figs 1–3.

Phyllodus sp. – Thurmond & Jones 1981: 104, fig. 48.

Material examined

UNITED STATES OF AMERICA – Alabama • 26 isolated teeth; Claiborne Group; MSC 188.104, MSC 35772.1–8, MSC 37338, MSC 37555.1–2, MSC 37913.5–15, MSC 38292.2–3, WSU 34.

Description

Isolated teeth of two morphologies, sub-oval and sub-circular. Teeth consisting of very low and thin, flat to weakly convex enameloid crown. Sub-rectangular teeth wider than long. Unworn teeth with very fine granular occlusal ornamentation; some worn teeth exhibit smooth medial wear facet. Basal surface is smooth, weakly concave, open. Tooth plates consisting of regularly stacked columns of teeth; teeth in medial row sub-oval, peripheral rows with sub-circular teeth, decreasing in diameter laterally. Teeth tightly packed with little interstitial bone.

Remarks

The basibrachial tooth plates in our sample were differentiated from those of Paralbula by the presence of regularly stacked columns of teeth, as opposed to irregularly stacked teeth in Paralbula. Complete Phyllodus tooth plates can be easily differentiated from those of Egertonia by the presence of a medial row of large sub-oval teeth (lacking in the latter genus) and by having teeth with a granular ornament. Partial Phyllodus tooth plates in our sample preserving only sub-circular peripheral teeth were differentiated from Egertonia by granular occlusal ornamentation and lack of a concentric ring at the tooth base. Isolated sub-circular (peripheral) teeth were identified using the same characteristics, however many had a crown that was too worn to preserve these features. These teeth were conservatively assigned to the Phyllodontidae only.

Because Phyllodus is only known from isolated teeth and tooth plates, its taxonomic affinities are somewhat unclear. Because this genus was not listed by Nelson et al. (2016), we follow Estes (1969) and Weems (1999) by placing Phyllodus within the Phyllodontidae. Historically, numerous species of Phyllodus have been named (see Leriche 1942; Casier 1966), but Estes (1969) considered these Cenozoic species to be nominal, suggesting they instead belonged to a single variable species, Phyllodus toliapicus. The variability observed within our sample supports this view, and we therefore refer all the teeth to this species.

Stratigraphic and geographic range in Alabama

The specimens in our sample were collected from the lower Tallahatta Formation at site ADl-1, the contact of the Tallahatta and Lisbon formations and the basal Lisbon Formation at site ACov-11, and the basal Gosport Sand at site ACl-4. Upper Ypresian to middle Bartonian, zones NP14 to NP17.