Distribution Geographic
Historic McConnico Plantation near Prairie Creek in Wilcox County, Alabama, USA, NW1/4, Sec. 32, T12N, R10E (U.S. Public Land Survey System) [32663]

Distribution Stratigraphy
Type stratum and age. Basal unnamed member, Porters Creek Formation, Paleocene, Danian Stage, zones NP3–4 [32663]

Description
Original description after Ebersole, Cicimurri & Harrell, 2024 [32663]:
Specimen GSA–V447 consists of 17 teeth that are herein assigned to anterior and lateral files of the upper and lower jaws. This assortment of teeth includes nine from the palatoquadrate (upper jaw) and eight from the Meckel’s cartilage (lower jaw). Teeth from both the left and right sides of the upper and lower jaws are represented, and it is possible that at least two of the teeth were derived from the same tooth file. Unfortunately, the limited number of teeth included with specimen GSA–V447 did not allow us to determine exactly how many anterior or lateral files were present within the dentition of this taxon, or how many posterior files occurred. However, based on the jaw sets of several extant lamniform sharks like Carcharodon carcharias, Isurus spp., Lamna nasus, and Odontaspis ferox (see Materials and Methods), we believe that upper and lower teeth are preserved, and both anterior and lateral tooth files are represented. Tooth morphologies we identified in GSA–V447 include:
Upper anterior teeth (GSA–V447.1, .6–.7, .11, Fig. 5a–p). We identified four teeth within this tooth group, including three complete specimens and one with an incomplete main cusp. Unlike the lateral teeth (see below), the sequential position within the jaw of P. bizzocoi sp. nov. is unknown because the total tooth height and root width of the upper anterior teeth is extremely variable within the extant lamniform jaws examined. The three complete teeth have a total height (TH) ranging between 28.87 and 29.16 mm and a root width (TW) that ranges from 18.84 to 19.99 mm. The height/width (H/W) ratios vary from 1.44 to 1.55 (Table 2). The three complete teeth (GSA–V447.1, .6–.7; Fig. 5a–k) have a tall and triangular main cusp. In labial view the main cusp is nearly symmetrical, but the mesial edge is slightly more convex than the distal edge, and this feature allows us to determine if they were derived from the left or right palatoquadrate. The labial face of the main cusp is slightly convex, whereas the lingual face is strongly convex. The mesial and distal cutting edges are complete and extend to the base of the main cusp. The crown enameloid is smooth except for faint plications occurring along the labial crown foot. The main cusp is slightly sinuous in profile view. The teeth have a single pair of diminutive lateral cusplets that are both medially and lingually hooked. Both lateral cusplets have mesial and distal cutting edges that do not connect to those on the main cusp. The root is bilobate, with lobes being divergent and of nearly equal length and width. The interlobe area is deep, wide, and U-shaped. The teeth have a robust lingual protuberance that is bisected by a deep nutritive groove. The height of the root represents approximately 30% of the total tooth height. Specimen GSA–V447.11 (Fig. 5m–p), the tooth with broken main cusp, is assigned to the upper anterior tooth group because it has a deeper interlobe area (8.44 mm) than any of the upper lateral teeth (see Table 2), the root lobes are shorter and more divergent than those on the lower teeth, and the interlobe area is wider and U-shaped compared to the lower anterior teeth (see additional discussion below). At least two upper anterior files are represented within GSA–V447 based on the slightly different dimensions and gross morphologies of teeth GSA–V447.6 and GSA–V447.7 (see Table 2). Both teeth have a narrow, triangular main cusp with cutting edges that are sub-parallel except near the apex, where they are biconvex. Tooth GSA–V447.7 (Fig. 5i–l) has a slightly narrower main cusp that is very slightly distally inclined compared to GSA–V447.6 (Fig. 5a–d), and it also has slightly longer root lobes. Teeth GSA–V447.1 and GSA–V447.6 have nearly identical dimensions (see Table 2), suggesting they belong to the same anterior file. Additionally, tooth GSA–V447.11 has a nearly identical root width to that of GSA–V447.7 (Fig. 5i–l), suggesting that these two teeth also represent the same anterior file.
Upper lateral teeth (GSA–V447.2–.3, .8–.10, Fig. 5q–ii). Five upper lateral teeth are preserved with GSA– V447, four of which are complete. The basal margins of the root lobes of tooth GSA–V447.9 are not preserved. The crowns of these teeth range in height from 17.64 to 11.4 mm, and the overall height of the complete teeth ranges from 23.93 to 15.59 mm. The H/W ratios range from 1.01 to 1.21 (Table 2). All the teeth have a triangular main cusp that is distally inclined in the anterolateral positions, but the cusp becomes shorter and more distally hooked the closer a tooth is positioned to the commissure. The labial and lingual faces of the main cusp are almost equally convex. In mesial or distal views, the main cusp is straight except for a slight labial bend at the apex. The crown enameloid is smooth except for very faint plications (visible under magnification) along the labial crown foot. There are one to two pairs of lateral cusplets, and when two pairs are present the larger pair is always positioned medially, and the lateral pair is much reduced in size. The larger pair of cusplets are distinctively hooked both medially and lingually. The main cusp cutting edges are complete and extend to the base of the main cusp. The cutting edges extend across the apical half of the lateral cusplets. A pair of minute mesial and distal denticulations occur between the main cusp and lateral cusplets on specimen GSA–V447.9 (Fig. 5u–x), but such denticles are absent on all other teeth associated with GSA–V447. The bilobate root has short and thin (labio-lingually) lobes that are divergent and rounded at their extremities. The interlobe area is wide and U-shaped. The pronounced lingual protuberance is bisected by a deep nutritive groove. Teeth GSA–V447.2 and GSA–V447.9 (Fig. 5u–bb) differ somewhat with respect to the degree of distal inclination of the main cusp, with GSA–V447.2 being slightly more inclined. These lateral teeth could be from succeeding lateral files, as for example GSA–V447.9 could be from the second lateral file and GSA–V447.2 the third lateral file. Tooth GSA–V447.3 (Fig. 5cc–ff) is slightly smaller in overall size and has a more distally inclined and curved crown compared to the other teeth assigned to this group, indicating that it is from a more distally located lateral file. Based on its small size and strongly distally hooked crown, tooth GSA–V447.10 (Fig. 5gg–ii) was likely part of a posterolateral file located closer to the jaw commissure, where the dental hollow is tapered and space for developing teeth is rather limited. One tooth, GSA–V447.8 (Fig. 5q–t), is believed to be from the upper dentition due to the distal inclination of the crown, and the short length of the root lobes and wide interlobe area. However, it exhibits an unusual morphology as it is significantly smaller than the anterior teeth and it is also conspicuously distally inclined. Additionally, the tooth is smaller than and/or lacks the distal crown curvature exhibited by the lateral teeth. Furthermore, the crown is mesio-distally thinner than all the other upper teeth. Specimen GSA–V447.8 conforms to our observations of the intermediate teeth of the extant lamniform shark dentitions we examined, although we cannot definitively rule out the possibility that it represents a lateral file.
Lower anterior teeth (GSA–V447.4, Fig. 6a–d). GSA–V447.4 is the only definitive lower anterior tooth associated with GSA–V447. This tooth measures 32.63 mm in total height and 17.28 mm in root width and has a H/W ratio of 1.89 (Table 2). The main cusp is tall and nearly symmetrical. Its labial face is slightly convex, whereas the lingual face is strongly convex. The crown enameloid is smooth save for faint plications occurring at the labial crown foot. The crown is weakly sigmoidal in mesial and distal views. There is a single pair of short lateral cusplets that are slightly lingually inclined. The mesial and distal cutting edges are incomplete and do not extend to the base of the main cusp. Smooth cutting edges extend across the lateral cusplets. The bilobate root has elongated, thin, and rounded lobes that are slightly divergent. The interlobe area is deep and U-shaped. The pronounced lingual protuberance is bisected by a deep nutritive groove. The crown height measures 19.9 mm, and this portion of the tooth comprises approximately 61% of the total height (Table 2). Two additional teeth associated with GSA–V447, GSA–V447.12–.13 (Fig. 6e–l), consist only of the main cusp and a portion of the root. These teeth are attributed to the lower dentition because the main cusp is not as sigmoidal as that of upper anterior teeth, the labial face is less convex compared to upper lateral teeth, and they have incomplete cutting edges. We believe these teeth represent lower anterior files because they have a more symmetrical main cusp compared to lower lateral teeth included with GSA–V447 (see below). Additionally, the main cusp height of these two teeth (18.59 and 18.09 mm, respectively) is greater than that of any lower lateral tooth (17.53 to 8.74 mm) (Table 2).
Lower lateral teeth (GSA–V447.5, 14–17, Fig. 6m–gg). Although five lower lateral teeth are part of GSA–V447, only one is complete (GSA–V447.5, Fig. 6q–t). The other four teeth have a complete main cusp but are missing one or both root lobes. These five teeth have a tall and narrow main cusp that has a very slight distal inclination. The slight distal inclination is most evident on the mesial side of the main cusp because the mesial edge is more convex than the distal edge near the apex. This morphology allowed us to determine if the tooth was from the right or left Meckel’s cartilage. The labial face of the main cusp is slightly convex, whereas the lingual face is strongly convex. The crown enameloid is smooth except for very faint plications (seen under magnification) along the labial crown foot. In mesial and distal views, the main cusp has a slight lingual inclination. The teeth generally have a single pair of lateral cusplets, but GSA–V447.1 (Fig. 6m–p) has a second diminutive distal cusplet that is united to the base of the much larger, more medially located cusplet. The lateral cusplets have a slight medial curve and are also lingually inclined. The mesial and distal cutting edges of the main cusp are incomplete, and the cutting edges that extend across the lateral cusplets do not meet the base of the main cusp. The bilobate root has lobes that are narrow, elongated, and slightly divergent. The interlobe area is deep and U-shaped. A robust lingual protuberance is bisected by a deep nutritive groove. The H/W ratio of GSA–V447.2 (complete tooth) is 1.74 (Table 2), and main cusp height on the five teeth ranges from 17.53 to 8.74 mm, indicating that overall tooth size decreased towards the commissure. Tooth GSA–V447.17 (Fig. 6cc–gg) has the shortest main cusp height of any tooth associated with GSA–V447 (Table 2), and this interesting tooth is regarded as a lower posterolateral tooth due to its small size but overall similarity to the other four teeth attributed to the lower lateral tooth group.

Remarks
shark-references Species-ID=17168

References