Palaeohypotodus bizzocoi, Ebersole & Cicimurri & Harrell Jr., 2024

Ebersole, Jun A., Cicimurri, David J. & Harrell Jr., T. Lynn, 2024, A new species of Palaeohypotodus Glueckman, 1964 (Chondrichthyes, Lamniformes) from the lower Paleocene (Danian) Porters Creek Formation, Wilcox County, Alabama, USA, Fossil Record 27 (1), pp. 111-134 : 111

Palaeohypotodus bizzocoi sp. nov.

Figs 4 , 5 , 6 , 7

Etymology.

The species is named for the late Bruce D. Bizzoco in honor of his dedicated volunteer service to MSC and his lifelong commitments to education and the preservation of local history in Alabama, USA.

Hypodigm.

GSA-V447.1 (holotype), upper left anterior tooth (Fig. 5a-d ); GSA-V447.2 (paratype), upper right lateral tooth (Fig. 5y -bb); GSA-V447.3 (paratype), upper right lateral tooth (Fig. 5cc-ff); GSA-V447.4 (paratype), lower right anterior tooth (Fig. 6a-d ); GSA-V447.5 (paratype), lower left lateral tooth (Fig. 6q-t ).

Referred specimens.

N = 29: GSA-V447.6, upper left anterior tooth, Porters Creek Formation, Wilcox County, AL; GSA-V447.7, upper left anterior tooth, Porters Creek Formation, Wilcox County, AL; GSA-V447.8, upper left lateral tooth, Porters Creek Formation, Wilcox County, AL; GSA-V447.9, upper right lateral tooth, Porters Creek Formation, Wilcox County, AL; GSA-V447.10, upper left lateral tooth, Porters Creek Formation, Wilcox County, AL; GSA-V447.11, upper anterior tooth, Porters Creek Formation, Wilcox County, AL; GSA-V447.12, lower left anterior tooth, Porters Creek Formation, Wilcox County, AL; GSA-V447.13, lower left anterior tooth, Porters Creek Formation, Wilcox County, AL; GSA-V447.14, lower right lateral tooth, Porters Creek Formation, Wilcox County, AL; GSA-V447.15, lower left lateral tooth, Porters Creek Formation, Wilcox County, AL; GSA-V447.16, lower left lateral tooth, Porters Creek Formation, Wilcox County, AL; GSA-V447.17, lower left lateral tooth, Porters Creek Formation, Wilcox County, AL; MMNS VP-7292.2, upper right lateral tooth, Pine Barren Member of the Clayton Formation, Lowndes County, AL; MMNS VP-7292.3, upper left lateral tooth, Pine Barren Member of the Clayton Formation, Lowndes County, AL; MMNS VP-7292.4, upper right lateral tooth, Pine Barren Member of the Clayton Formation, Lowndes County, AL; MMNS VP-7295.4, upper right posterior tooth, Pine Barren Member of the Clayton Formation, Lowndes County, AL; MMNS VP-7311, lower right lateral tooth, Pine Barren Member of the Clayton Formation, Lowndes County, AL; MMNS VP-8578, upper right lateral tooth, basal Clayton Formation, Hot Spring County, AR; MSC 3020, lower left anterior tooth, lower Clayton Formation, Wilcox County, AL; MSC 42727, upper right lateral tooth, Pine Barren Member of the Clayton Formation, Lowndes County, AL; MSC 42733, upper right lateral tooth, Pine Barren Member of the Clayton Formation, Lowndes County, AL; MSC 42741.4, upper right lateral tooth, Pine Barren Member of the Clayton Formation, Lowndes County, AL; MSC 42741.5, upper right lateral tooth, Pine Barren Member of the Clayton Formation, Lowndes County, AL; MSC 42742.1, upper right lateral tooth, Pine Barren Member of the Clayton Formation, Lowndes County, AL; MSC 42742.2, upper right lateral tooth, Pine Barren Member of the Clayton Formation, Lowndes County, AL; MSC 42742.3, upper right lateral tooth, Pine Barren Member of the Clayton Formation, Lowndes County, AL; MSC 49451, upper left lateral tooth, lower Clayton Formation, Wilcox County, AL; MSC 49452, upper left 3rd anterior tooth, Porters Creek Formation, Butler County, AL; MSC 49454, upper left lateral tooth, lower Clayton Formation, Wilcox County, AL.

Type stratum and age.

Basal unnamed member, Porters Creek Formation, Paleocene, Danian Stage, zones NP3-4 (Fig. 3 ).

Type locality.

Historic McConnico Plantation near Prairie Creek in Wilcox County, Alabama, USA, NW1/4, Sec. 32, T12N, R10E (U.S. Public Land Survey System) (Figs 1 , 2 ).

Description.

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.

Our analysis of the 17 teeth included with GSA-V447 indicates that monognathic and dignathic heterodonty were developed within the dentition of Palaeohypotodus bizzocoi sp. nov. Our examination of 17 isolated teeth from temporally equivalent strata also indicate a degree of ontogenetic heterodonty within this taxon.

Monognathic heterodonty. Some of the variation observed amongst the teeth within GSA-V447 reflects the presence of anterior and lateral tooth files in the palatoquadrate and Meckel’s cartilage of P. bizzocoi sp. nov. (Fig. 7 ). Upper anterior teeth differ from upper lateral teeth by having a taller and mesiodistally narrower main cusp, and the H/W ratios of anterior teeth range from 1.44-1.55 but those of lateral teeth are much lower at 1.01-1.21 (Table 2 ). The main cusp of anterior teeth is also more erect, more symmetrical, and labiolingually thicker compared to the inclined to strongly distally hooked crown of lateral teeth. Additionally, the anterior teeth have longer and less divergent root lobes and a deeper interlobe area than lateral teeth. The root height is therefore lower on lateral teeth (between 26.3 to 28.9% the height of the tooth) than on anterior teeth (between 30.1 and 32.1%) because of the shorter root lobes. Furthermore, the lateral teeth can have up to two pairs of lateral cusplets but there is only one pair on the anterior teeth. Lastly, although the teeth of the Meckel’s cartilage are similar to one another, the lateral teeth are characterized by the slight distal inclination of the main cusp (Fig. 6 ). Additionally, the root of GSA-V447.5 shows that lobes are more widely separated compared to the complete anterior tooth (GSA-V447.4).

Dignathic heterodonty. The teeth included with GSA-V447 also demonstrate morphological variation between the teeth of the palatoquadrate and Meckel’s cartilage of P. bizzocoi sp. nov. (Figs 5 , 6 ). Overall, the upper teeth differ from the lower teeth by having a wider U-shaped interlobe area, as the root lobes on the upper teeth are shorter and more divergent. This is reflected in the H/W ratios among the teeth, which are much higher for lower teeth (1.74 to 1.89) than for the uppers (1.01 to 1.55) (Table 2 ). In addition, the height of the root constitutes between 26-32% of total tooth height of upper teeth and between 36-39% of lower teeth.

Upper anterior teeth (i.e., GSA-V447.1, 6-7, Fig. 5a-p ) are distinguished by their complete cutting edges, whereas those of lower anterior teeth (i.e., GSA-V447.4, Fig. 6a-d ) do not reach the main cusp base. In profile view, the upper anterior teeth have a more sigmoidal main cusp compared to the lower anterior files. Additionally, the lateral cusplets on upper anterior teeth are lingually curved but those on the lower anterior teeth have a slight distal inclination. With respect to the tooth root, that of the upper anterior teeth has shorter and more divergent lobes compared to lower anterior teeth, and the interlobe area is resultantly more widely U-shaped on the upper anterior teeth. Furthermore, the root comprises 30-32% of the total height of upper anterior teeth but is close to 40% on the lower anterior tooth GSA-V447.4 (Table 2 ).

The lower lateral teeth are easily differentiated from upper lateral teeth by their narrower and nearly vertical main cusp with relatively flat labial face. In contrast, the upper lateral teeth are conspicuously distally inclined to strongly distally hooked, and the labial crown face is more convex. In addition, the mesial and distal cutting edges of the main cusp on lower lateral teeth are incomplete, whereas they extend to the lateral cusplets on the upper lateral teeth. The main cusp of lower lateral teeth is also slightly curved lingually near the apex, whereas upper lateral teeth have a straighter lingual crown face. Furthermore, the lateral cusplets of lower lateral teeth have a slight distal inclination, whereas those of the upper teeth are distally curved. Moreover, the lateral teeth have a deeper interlobe area due to more elongated but less divergent root lobes compared to the upper lateral teeth. Lastly, the root height of the only complete lower lateral tooth in our sample (GSA-V447.5) constitutes 36.4% of the total tooth height, which far exceeds that on any of the upper lateral teeth (only 26.9% to 28.9%; see Table 2 ).

Ontogenetic heterodonty. The 17 teeth included with GSA-V447 were derived from the Danian Porters Creek Formation in Wilcox County, AL. No additional P. bizzocoi sp. nov. specimens are known from the type locality, but the collections at MSC and the MMNS include 17 isolated teeth collected from Alabama and Arkansas, USA (see Referred specimens above) that we associate with this new species. One of these teeth (MSC 49452) was collected from the type stratum (albeit from a different locality), whereas the other 16 teeth were derived from lithostratigraphic units that are temporally equivalent to the Porters Creek Formation. Two specimens in particular, MSC 49451 and MMNS VP-8578, are morphologically, qualitatively, and quantitatively comparable to teeth within GSA-V447. Specifically, MSC 49451 (Fig. 7a-d ) is an upper left lateral tooth that is nearly indistinguishable from the P. bizzocoi sp. nov. paratype tooth GSA-V447.3 (Fig. 5cc-ff) in terms of size and gross morphology (see Tables 2 , 3 ). In addition, specimen MMNS VP-8578 (Fig. 7e-h ), an upper right lateral tooth, is nearly identical in all respects to P. bizzocoi sp. nov. paratype tooth GSA-V447.2 (Fig. 5y -bb). The morphological similarity of the 17 isolated teeth to those included with GSA-V447 leads us to conclude that they represent P. bizzocoi sp. nov. and that they reflect intraspecific (ontogenetic) variation within the species.

Ten of the additional 17 isolated teeth referred to P. bizzocoi sp. nov. are complete and could be described in their entirety and measured, allowing us to directly compare them to the teeth of GSA-V447. One of the referred specimens was identified as a posterior tooth (see below) and was excluded from our quantitative analysis due to its atypical morphology.

Our quantitative evaluation of the total tooth sample of P. bizzocoi sp. nov. revealed several morphological trends that we interpret to represent ontogenetic heterodonty within the species. Table 3 lists all the complete teeth according to tooth group (i.e., upper and lower anterior and upper and lower lateral) and are presented by ascending order of total tooth height (TH). Our data shows that the teeth associated with GSA-V447 are among the largest in our sample, indicating these specimens likely represent adult individuals (or a single adult individual). Interestingly, specimen MSC 3020 (Fig. 7q-t ), a lower anterior tooth, has a TH over 5 mm greater than the largest lower anterior tooth associated with GSA-V447 (paratype tooth GSA-V447.4), indicating that this species could achieve even larger sizes than indicated by the type specimens.

One morphological trend that is evident in Table 3 is the ontogenetic reduction in the number of lateral cusplets on upper teeth. Of the upper anterior teeth in our sample, all the specimens with a TH less than 24 mm have two pairs of lateral cusplets, whereas those with a TH greater than 24 mm only have a single pair. Additionally, the number of lateral cusplets on the upper lateral teeth ranges from one to three pairs, but the occurrence of three pairs is limited to teeth with a TH of 13 mm or less. In contrast, all upper lateral teeth that exceed 15 mm in TH have a maximum of two lateral cusplet pairs. Similarly, the number of lateral cusplets on each side of the main cusp on lower anterior and lateral teeth also does not exceed two, with most specimens having a single pair regardless of tooth size. We observed that the mesial and distal cusplets on teeth of both the palatoquadrate and Meckel’s cartilage can be unequal in number (Tables 2 , 3 ), particularly on lateral teeth.

Our data shows a general trend across all tooth groups of both the palatoquadrate and Meckel’s cartilage that, as the TH of a tooth increases, the total width (TW), main cusp height (MCH), main cusp width (MCW), root height (RT), root thickness (RT), and depth of the interlobe area (DIA) also increases (see Table 3 ). These trends reflect ontogenetic change from small and gracile teeth in juvenile stages to large and robust teeth into adulthood. Interestingly, when the ratio of the root to overall tooth height is calculated (%RH) and then compared to that of the main cusp (%MCH), these values show an inverse relationship through ontogeny. As the shark matures the %RH increases and the %MCH decreases, which is a result of an increase in the length of the mesial and distal root lobes through ontogeny. This is also reflected in the DIA (i.e., depth of the interlobe area), which increases (deepens) as the root lobes become elongated (Table 3 ). Although subtle changes are evident across ontogeny based on the aforementioned values, the height/width ratios (H/W) remain relatively constant. This indicates that juvenile teeth, at least in terms of H/W ratios, are essentially smaller versions of the larger teeth, with any differences in the values likely being a result of different tooth files within a particular tooth group (for example, a lower second versus lower third anterior).

Additional tooth files. In addition to elucidating ontogenetic heterodonty, the sample of 17 isolated P. bizzocoi sp. nov. teeth increases our understanding of monognathic and dignathic heterodonty within the species. Included in the sample are two tooth positions that are not represented amongst the teeth associated with GSA-V447. One of these teeth, MSC 49452 (Fig. 7z -cc), has a tall and triangular main cusp, two pairs of lingually curved lateral cusplets, complete mesial and distal cutting edges, plications along the labial crown base, a pronounced lingual root protuberance with nutritive groove, and a deep U-shaped interlobe area, which are all characteristics of P. bizzocoi sp. nov. anterior teeth. However, this tooth also has an elongated and mesially extended mesial root lobe, and the distal edge of the main cusp is more convex than the mesial edge, giving the main cusp a slight mesial curve (as opposed to distally inclined or hooked). Of the extant lamniform dentitions we examined, these unique characteristics are remarkably similar to those of the upper third anterior teeth of Carcharias taurus and Mitsukurina owstoni .

Specimen MMNS VP-7295.4 is herein regarded as an upper posterior tooth of P. bizzocoi sp. nov. (Fig. 7u-y ). This tooth is very small and measures 5.4 mm in TH and 6.4 mm in RW. The tooth has a short and distally hooked main cusp and although the lateral cusplets are not preserved on this tooth, it appears to have had at least one pair. The mesial and distal cutting edges are complete and extend to the base of the lateral cusplets. The root is robust and, in lingual view, the height of the root (3.8 mm) is more than twice the height of the crown (1.6 mm). The root lobes are short, rounded, divergent, and form a wide and U-shaped interlobe area. The lingual face of the root is bisected by a deep nutritive groove. Perhaps the most conspicuous feature of this tooth is the extensive ornamentation along the labial crown foot, where enameloid plications coalesce into spine-like structures. Similar ornamentation has been reported on posterolateral and posterior teeth of Palaeohypotodus rutoti (see Herman 1972, pl. 2, figs 1-3, 5; Herman 1977, pl. 10, fig. 3e; Cappetta 2012, fig. 192h-j), and this specific characteristic was noted by Leriche (1902, 1906) and Herman (1972, 1977). This phenomenon indicates a degree of dental homology and stasis between the temporally younger P. rutoti and the Danian P. bizzocoi sp. nov.

Figures

Figure 1. Geologic map of Wilcox County showing the approximate location of the McConnico Plantion (indicated by red star). Scale bar applies to Wilcox County map.

Figure 2. Location of McConnico Plantation in Wilcox County, AL, USA; a. Portion of a historical property map of Wilcox County, AL (Crump 1870) showing the location of the McConnico Plantation (red polygon). b. Portion of a geologic map of Wilcox County, AL (LaMoreaux and Toulmin 1959) showing the location of the McConnico Plantation (red polygon) and the area where GSA-V 447 was likely recovered (red star). Arrows indicate the location of Smith's Bridge which is a landmark for orientation. Qal = Quaternary alluvium, Tc = Clayton Formation, Tp = Porters Creek Formation.

Figure 3. Stratigraphic column of early-to-middle Paleocene strata of Alabama. Red dot indicates the likely horizon of GSA-V 447. Column is based on Raymond et al. (1988) and modified with data from Gibson et al. (1982), Mancini et al. (1989), Mancini and Tew (1993), and Ogg et al. (2016).

Figure 4. Standard tooth measurements. a-c. GSA-V 447.6, Palaeohypotodus bizzocoi sp. nov. upper anterior tooth; a. Labial view; b. Mesial view; c. Lingual view; DIA - Depth of the interlobe area; MCH - Main cusp height; RH - Root height; RT - root thickness; RW - Root width; TH - Total height; Scale bar: 1 cm.

Figure 5. (a-ii) Palaeohypotodus bizzocoi sp. nov. upper teeth. a-d. GSA-V 447.6, upper left anterior tooth; a. Labial view; b. Lingual view; c. Mesial view; d. Basal view. e-h. GSA-V 447.1 (holotype), upper left anterior tooth; e. Basal view; f. Labial view; g. Lingual view; h. Mesial view. i-l. GSA-V 447.7, upper right anterior tooth; i. Labial view; j. Lingual view; k. Mesial view; l. Basal view. m-p. GSA-V 447.11, upper anterior tooth; m. Basal view; n. Labial view; o. Lingual view; p. Profile view. q-t. GSA-V 447.8, upper left intermediate or lateral tooth; q. Labial view; r. Lingual view; s. Mesial view; t. Basal view. u-x. GSA-V 447.9, upper right lateral tooth; u. Basal view; v. Labial view; w. Lingual view; x. Mesial view. y-bb. GSA-V 447.2 (paratype), upper right lateral tooth; y. Labial view; z. Lingual view; aa. Mesial view; bb. Basal view. cc-ff. GSA-V 447.3 (paratype), upper right lateral tooth; cc. Basal view; dd. Labial view; ee. Lingual view; ff. Mesial view. gg-ii. GSA-V 447.10, upper left lateral tooth; gg. Labial view; hh. Lingual view; ii. Mesial view. Scale bars: 1 cm.

Figure 6. a-gg. Palaeohypotodus bizzocoi sp. nov. lower teeth. a-d. GSA-V 447.4 (paratype), lower right anterior tooth; a. Labial view; b. Lingual view; c. Mesial view; d. Basal view. e-h. GSA-V 447.12, lower right anterior tooth; e. Basal view; f. Labial view; g. Lingual view; h. Mesial view. i-l. GSA-V 447.13, lower right anterior tooth; i. Basal view; j. Labial view; k. Lingual view; l. Mesial view. m-p. GSA-V 447.14, lower right lateral tooth; m. Labial view; n. Lingual view; o. Mesial view; p. Basal view. q-t. GSA-V 447.5 (paratype), lower left lateral tooth; q. Labial view; r. Lingual view; s. Mesial view; t. Basal view. u-x. GSA-V 447.15, lower left lateral tooth; u. Basal view; v. Labial view; w. Lingual view; x. Mesial view. y-bb. GSA-V 447.16, lower left lateral tooth; y. Labial view; z. Lingual view; aa. Mesial view; bb. Basal view. cc-gg. GSA-V 447.17, lower right lateral tooth; cc. Basal view; dd. Labial view; ee. Lingual view; ff. Mesial view; gg. Close-up of labial crown ornamentation. Scale bars: 1 cm.

Figure 7. Palaeohypotodus bizzocoi sp. nov. referred specimens. a-d. MSC 49451, upper left lateral tooth, lower Clayton Formation, Wilcox County, AL; a. Labial view; b. Lingual view; c. Mesial view; d. Basal view. e-h. MMNS VP- 8578, upper right lateral tooth, basal Clayton Formation, Hot Spring County, AR; e. Basal view; f. Labial view; g. Lingual view; h. Mesial view. i-l. MMNS VP- 7292.3, upper right lateral tooth, Pine Barren Member of the Clayton Formation, Lowndes County, AL; i. Labial view; j. Lingual view; k. Mesial view; l. Basal view. m-p. MSC 42733, upper left lateral tooth, Pine Barren Member of the Clayton Formation, Lowndes County, AL; m. Basal view; n. Labial view; o. Lingual view; p. Mesial view. q-t. MSC 3020, lower left anterior tooth, lower Clayton Formation, Wilcox County, AL; q. Labial view; r. Lingual view; s. Mesial view; t. Basal view. u-y. MMNS VP- 7295.3, upper right posterior tooth, Pine Barren Member of the Clayton Formation, Lowndes County, AL; u. Close-up of labial crown ornamentation; v. Labial view; w. Lingual view; x. Mesial view; y. Basal view. z-cc. MSC 49452, upper left 3 rd anterior tooth, Porters Creek Formation, Butler County, AL; z. Basal view; aa. Labial view; bb. Lingual view; cc. Mesial view. Scale bars: 1 cm (a-h, q-t, z-cc); 5 mm (i-p, v-y).