Physogaleus contortus ( Gibbes, 1849 )

Cicimurri, David J., Ebersole, Jun A., Stringer, Gary L., Starnes, James E. & Phillips, George E., 2025, Late Oligocene fishes (Chondrichthyes and Osteichthyes) from the Catahoula Formation in Wayne County, Mississippi, USA, European Journal of Taxonomy 984 (1), pp. 1-131 : 26-27

Physogaleus contortus ( Gibbes, 1849)

Fig. 7A –DD

Galeocerdo contortus Gibbes, 1849: 193 .

Material examined

UNITED STATES OF AMERICA – Mississippi • 15 isolated teeth; Catahoula Formation ; MMNS VP-6623 (3 teeth), MMNS VP-6623.1 ( Fig. 7D–F ), MMNS VP-6623.2 ( Fig. 7J–L ), MMNS VP-6623.3 ( Fig. 7M–O ), MMNS VP-6623.4 ( Fig. 7P–R ), MMNS VP-6623.5 ( Fig. 7S–U ), MMNS VP-6623.6 ( Fig. 7V–X ), MMNS VP-6623.7 ( Fig. 7Y –AA), MMNS VP-6623.8 ( Fig. 7 BB–DD), MMNS VP-12047 ( Fig. 7A–C ), SC 2013.28.106 ( Fig. 7G–I ), SC 2013.28.107 , SC 2013.28.108 .

Description

Teeth are broad-based and moderately high-crowned, with the largest specimens measuring 15 mm in mesio-distal width and 12 mm in apico-basal height. The crown of each specimen consists of a conspicuous cusp and distal heel. The mesial cutting edge is elongated and sinuous, with the basal portion being concave and the apical portion convex; the degree of curvature in these areas is variable (i.e., weakly to strongly). The cutting edge is also serrated to varying degrees, and it may be finely and evenly serrated along nearly its entire length or coarse along a portion but fine along another portion of the same edge. Serrations are often coarse basally but fine apically. In mesial view, the cutting edge is usually very sinuous, and the apical portion of the cusp has a twisted appearance that is particularly conspicuous in mesial view ( Fig. 7C, I , AA). The distal cutting edge is comparatively much shorter, distally inclined, and finely serrated. The mesial and distal cutting edges intersect apically to form a rather narrow, elongated, and distally inclined cusp. The serrations on the distal cutting edge are coarsest basally but fine apically. Serrations on the mesial and distal cutting edges are simple. The transition from distal cutting edge to distal heel is marked by a sharp curve or a notch (compare Fig. 7 BB to 7G), and on the former serrations occur within the curve and onto the apical edge of the first denticle on the heel ( Fig. 7M ). On the latter, the apical portion of the first denticle on the heel is serrated ( Fig. 7V ). The distal heel is low, elongated, oblique to a vertical plane, and denticulated. Typically, there are at least four conspicuous denticles that decrease in size distally, where they blend into serrations near the crown margin. Denticles on the distal heel are often weakly serrated on their apical edges. The root is bilobate with thin, short but widely separated lobes. The prominent lingual root boss on each specimen is ablated but was bisected by a nutritive groove ( Fig. 7T , CC).

Remarks

Cicimurri et al. (2022) reported similar specimens from the Rupelian Ashley Formation of South Carolina, and they discussed the stratigraphic and temporal ambiguity surrounding the morphology of P. contortus as originally described by Gibbes (1849). In short, Gibbes noted that his South Carolina specimens originated from “newer Eocene” deposits, which, based on fossil content, almost certainly belong to the Ashley Formation due to the Rupelian age of the associated invertebrates he identified. Gibbes (1849) specifically noted the twisted appearance of the mesial cutting edge ( Fig. 7C, F ), and the specimens he illustrated, particularly as seen in his figs 71–72, have coarse distal heel denticles. This latter morphology conforms to the Oligocene specimens we collected from the Catahoula Formation, as well as to the material reported by Cicimurri et al. (2022). We examined Miocene and Pliocene teeth typically assigned to P. contortus that were collected from North and South Carolina and Florida, and specimens of this age have a more evenly serrated heel compared to the Oligocene counterparts. We must therefore take into consideration the possibility that Gibbes’ original concept of the contortus morphology was for Oligocene Ashley Formation specimens. That the distal cutting edge serrations of the Catahoula Formation specimens are already encroaching onto the distal heel foreshadows the development of a uniformly serrated heel in the Mio-Pliocene descendants of the Oligocene taxon. The specimens in our sample represent the first occurrence of P. contortus from the northern Gulf Coastal Plain of the USA

The Catahoula Formation P. contortus teeth exhibit monognathic heterodonty, with anterior teeth being mesio-distally narrow and having a rather erect cusp ( Fig. 7D–E ), and lateral teeth being wider and having a more distally inclined cusp ( Fig. 7A–B ). Additionally, cusp inclination increases but height decreases towards the commissure (compare Fig. 7J and P ). The teeth vary considerably in the width of the cusp and the convexity of the mesial cutting edge, which we believe reflects dignathic heterodonty. Teeth that may be from upper files are those shown in Fig. 7A, G , and V, whereas those from lower files are shown in Fig. 7M, S , and Y.

The Catahoula Formation P. contortus teeth can be separated from Galeocerdo (see below) by their elongated and narrow cusp, simple serrations, lack of serrations at the cusp apex, and the “twisted” nature of the mesial cutting edge. The teeth of Galeocerdo that we examined, including fossil and extant specimens, have a straight mesial cutting edge (in mesial and occlusal views), and most of the Galeocerdo species have compound serrations ( Türtscher et al. 2021). The Oligocene P. contortus morphology should therefore be separable from specimens identified as the “narrow crowned” morphology of G. aduncus ( Agassiz, 1835) (i.e., Türtscher et al. 2021) by this contorted apical portion of the cusp. The Catahoula Formation P. contortus teeth differ from those we assigned to Physogaleus sp. (see below) by being larger in overall size and by having a more elongated and usually sinuous cusp, conspicuous mesial serrations extending more than two-thirds along the edge, more numerous and well-developed distal denticles, and fine serrations that extend nearly to the apex of the distal cutting edge of the main cusp. Pollerspöck and Unger (2023) recently suggested P. contortus be placed within Galeocerdonidae , which was followed by Höltke et al. (2024). However, doing so necessitates placing all other species of Physogaleus , which are quite different from Galeocerdo , within the family, or assigning the contortus morphology to Galeocerdo . Based on the criteria we utilized to differentiate P. contortus from Galeocerdo , we maintain the former taxon within Carcharhinidae .

Figures

Fig. 7. Physogaleus contortus (Gibbes, 1849) (A–DD) and Physogaleus sp. (EE–JJ), teeth. A–C. MMNS VP-12047, Physogaleus contortus, antero-lateral tooth. A. Labial view. B. Lingual view. C. Mesial view. D–F. MMNS VP-6623.1, P. contortus, anterior tooth. D. Labial view. E. Lingual view. F. Mesial view. G–I. SC2013.28.106, P. contortus, lateral tooth. G. Labial view. H. Lingual view. I. Mesial view. J–L. MMNS VP-6623.2, P. contortus, anterior tooth. J. Labial view. K. Lingual view. L. Mesial view. M–O. MMNS VP-6623.3, P. contortus, lateral tooth. M. Labial view. N. Lingual view. O. Mesial view. P–R. MMNS VP-6623.4, P. contortus, lateral tooth. P. Labial view. Q. Lingual view. R. Mesial view. S–U. MMNS VP-6623.5, P. contortus, anterior tooth. S. Labial view. T. Lingual view. U. Mesial view. V–X. MMNS VP-6623.6, P. contortus, anterior tooth. V. Labial view. W. Lingual view. X. Mesial view. Y–AA. MMNS VP-6623.7, P. contortus, lateral tooth. Y. Labial view. Z. Lingual view. AA. Mesial view. BB–DD. MMNS VP-6623.8, P. contortus, antero-lateral tooth. BB. Labial view. CC. Lingual view. DD. Mesial view. EE–GG. SC2013.28.134, Physogaleus sp., tooth. EE. Labial view. FF. Lingual view. GG. Mesial view. HH–JJ. SC2013.28.136, Physogaleus sp., tooth. HH. Labial view. II. Lingual view. JJ. Mesial view. Scale bars: A–DD = 1 cm; EE–JJ = 2 mm.