Cardabiodon ricki Siverson, 1999

Newbrey, Michael G., Siversson, Mikael, Cook, Todd D., Fotheringham, Allison M. & Sanchez, Rebecca L., 2015, Vertebral morphology, dentition, age, growth, and ecology of the large lamniform shark Cardabiodon ricki, Acta Palaeontologica Polonica 60 (4), pp. 877-897 : 882-891

Cardabiodon ricki Siverson, 1999

Holotype: WAM 96.4.45, vertebrae and 104 teeth from uppermost 10 cm of the Gearle Siltstone (middle Cenomanian), CY Creek, Giralia Range, Western Australia.

Material. —WAM 96.4.45 and WAM 96.3.175.

Emended diagnosis. —Anterior teeth not enlarged relative to largest lateroposterior teeth. Multiple files of full-sized teeth equipped with massive root, somewhat mesiodistally compressed lobes, and distally curved apical half of cusp. Two types of reduced teeth with erect symmetrical cusp in dentition, including larger type (2/3 height of tallest anterior teeth) with labiolingually compressed root and smaller type (1/2 height of tallest anterior teeth) with mesiodistally compressed root. Minute, rounded cusplet commonly present between cusp and main cusplets. Cusplets reduced on full-sized anterior teeth with upright cusp. Lingual neck very wide medially. Diameter of largest vertebral centrum approximately 2.5 times height of tallest tooth in dentition. Centra of medium length and round. Corpus calcareum thick with laterally flat rims. Radial lamellae robust, widely spaced. Concentric lamellae absent. Small circular or subovate pores concentrated next to each corpus calcareum in the vicinity of the dorsal and ventral articular foramina. Papillose circular ridges on the surface of the corpus calcareum.

Dental morphology. — Siverson (1999) reconstructed the dentition of Cardabiodon ricki from CY Creek (middle Cenomanian) based on 100 teeth from a single individual (WAM 96.4.45). Four additional teeth pertaining to the holotype have since been collected (WAM 96.4.45.124–127). In his reconstruction, Siverson (1999: fig. 5) indicated that two tooth positions in the lower jaw were missing; lp10 and lp13. In modern lamnids, the ecological equivalents to Cardabiodon ricki (i.e., selachian apex predators), the most posteriorly situated teeth diminish in size more rapidly than shown in the reconstruct- ed dentition of the holotype of Cardabiodon ricki (e.g., Bass et al. 1975: pls. 8 and 9; Compagno 2001: figs. 78, 79). We suspect that the two “missing” tooth files were never present (teeth from these “missing” tooth files have not been recovered despite collection of additional teeth belonging to the holotype individual following the publication of Siverson’s [1999] paper). This would reduce the number of putative lower lateroposterior teeth from 14 to 12 in WAM 96.4.45 ( Fig. 4 ).

The teeth assigned to the anterior tooth files in WAM 96.4.45 differ from those assigned to the lateroposterior files by having a massive root with lobes exhibiting a circular cross-section (lobes are labiolingually compressed in the assigned lateroposterior teeth). The lateroposterior teeth in WAM 96.4.45 can be separated into two groups based on their profile view. One group comprises teeth with a slightly to strongly labially curved cusp in profile view (e.g., Siverson 1999: fig. 7.6B) and the other group comprises teeth with a slightly to strongly lingually curved cusp in profile view (e.g., Siverson 1999: fig. 10.6B). Teeth of the latter group are wider and have a more erect cusp. By comparison with extant macrophagous lamnid sharks ( Isurus spp. , Carcharodon carcharias , Lamna spp. ), the latter group of teeth exhibit one character typical for teeth of the upper jaw (great width) and two characters indicating a lower jaw position (more upright cusp in labial/lingual views and a lingually curved cusp in profile view). On the basis of these characteristics, and the degree of root symmetry versus absolute tooth size, the latter group was assigned to the lower jaw and the former group (narrow teeth with a cusp that is distally curved in lingual/ labial views and labially curved in profile view) to the upper jaw by Siverson (1999), a designation followed here.

The diagnosis of Cardabiodon ( Siverson 1999) relies in part on hypothesized dentition morphology. It therefore seems prudent to present a revised, somewhat more objective diagnosis. Nevertheless, regardless of how the teeth of WAM 96.4.45 are arranged, it is clear that the dentition design is not comparable to that of any other extinct or extant lamniform genus. The reduced anterior teeth are a particularly conspicuous feature in Cardabiodon that sets it apart from living macrophagous lamniforms.As reconstructed by Siverson (1999), there is a unique, abrupt increase in tooth size at the anterior/ lateroposterior transition in the lower jaw. The designated a4 has a cusp and root comparable to those of the most distal lower anterior tooth of Isurus oxyrinchus . Apart from having a strongly lingually curved cusp in profile view (a typical feature in anteriorly situated lower anterior teeth of modern macrophagous lamniforms) its labial/lingual profile view is similar to that of the reduced first upper lateroposterior tooth in I. oxyrinchus . In the latter species, the LP 1 has a labially curved cusp in profile view as opposed to the strongly lingually curved cusp on the designated a4 of WAM 96.4.45. A perfect match for a LP 1 (reduced size, strongly asymmetrical root and a labially curved cusp in profile view) is indeed present among the teeth of WAM 96.4.45.30 ( Siverson 1999: fig. 8.7), indicating that the assigned a4 is not a misplaced anteriorly situated upper lateroposterior tooth. The direction of the lateral cusplets in the assigned a4 is very similar to that in the putative lp1 and lp2 ( Siverson 1999: fig. 5).

The juvenile Cardabiodon ricki tooth (WAM 13.6.1) is derived from the basal 0.1 m of the Haycock Marl (= Beedagong Claystone of Siverson 1996) in the lower Murchison River area, Western Australia. Recent work on selachians from the basal part of the Haycock Marl indicates a late Cenomanian or early Turonian age ( Cretoxyrhina teeth corresponding in morphology with those from the Greenhorn Limestone in Kansas [Mike Everhart collection], below the Collignoniceras woollgari Zone ). This age determination is supported by nannofossil data (Watkins in Gunson 1995) and the laminated appearance of the mid- to outer shelf sediment, indicating that it was formed during the Cretaceous Oceanic Anoxic Event II.

The very small, juvenile tooth is assigned to Cardabiodon ricki on the basis of its extremely wide neck and greatly elongated outer cutting edge of the mesial cusplet (see Siverson 1999: fig. 10.4B). The compressed, flared out root indicates that it belonged to a very young individual as this feature is only present in the very smallest teeth of Cardabiodon venator (e.g., WAM 04.10.91). A similar root, distinctly different from that in larger juveniles and adults, characterised the smallest juvenile tooth of another extinct lamniform shark, Carcharocles megalodon (Agassiz, 1843) , described and illustrated by Pimiento et al. (2010: fig. 2, specimen UF 237959). Labial and lingual folds are absent on all juvenile teeth examined of early middle Turonian Cardabiodon venator (see Siverson and Lindgren 2005). Their presence on the Haycock Marl tooth is likely a result of its older geological age (the occurrence of folds on the crown increases with increasing geological age in Cretaceous lamniform genera; MS personal observations) and very early ontogenetic stage (e.g., the smallest teeth of Dwardius woodwardi [ Herman, 1977] from the basal Haycock Marl do likewise have folds on the crown). The labial base of the crown forms a shelf relative to the labial face of the root. This feature, absent in large teeth of Cardabiodon , likewise characterises juvenile teeth of Cardabiodon venator ( Siverson and Lindgren 2005) . Although WAM 13.6.1 represents the only known occurrence of Cardabiodon ricki in the basal Haycock Marl, the species is present (large lower anterior tooth) in the uppermost bed of the underlying “Upper” Gearle Siltstone (WAM 13.8.1) and Cardabiodon venator occurs in the overlying nodule bed at the Haycock Marl/Toolonga Calcilutite contact (see Siverson 1996: pl. 4: 8–10). The presence of a very young Cardabiodon in the basal Haycock Marl follows the pattern seen in D. woodwardi , Cretoxyrhina agassizensis , Johnlongia allocotodon Siverson, 1996 , Squalicorax sp. (described as S. volgensis by Siverson 1996) and Echinorhinus sp. , all of which are represented largely or almost exclusively by teeth from small juveniles in this part of the section.

Vertebral centra. — An examination of the Cardabiodon ricki centra from the two individuals from the CY Creek localities indicates that centrum morphology is very similar. Although WAM 96.3.175, comprising four associated centra, was found without teeth, it is also assumed to belong to Cardabiodon ricki based on similar proportions and shared characteristics including robust radial lamellae, very thick corpus calcareum, no concentric lamellae, and other characteristics as described and diagnosed below.

Examined precaudal centra of Cardabiodon ricki are large midtrunk centra (i.e., relative to the posterior precaudal centra) comparable in diameter to those of Cretoxyrhina mantelli (WAM 96.4.45.128, 96.3.175.1) ( Figs. 5A, B , 6 ). The midtrunk centra are 2.3–3 times wider than they are long and have a double-cone (biconcave) calcification with slightly convex lateral sides. The centrum from the holotype (WAM 96.4.45.128) is incomplete but has a radius of 42 mm, suggesting a diameter of 84 mm ( Fig. 5A ), and a length of 30 mm. The ventral, articular interforamen width is 36 mm and the interforamen angle is 65°. The second centrum (WAM 96.3.175.1) measures 72 mm in diameter and 32 mm in length ( Fig. 5B ). The neural arch interforamen width is 12 mm and the interforamen angle is 45°. The neural arch interforamen and intraforamen widths are the same. The ventral interforamen width is 25 mm with an interforamen angle of 64°. The midtrunk dorsal foramina for articulation with the neural arch are large rectangles with rounded corners and abut the anterior corpus calcareum (WAM 96.3.175.1). The neural arch foramina extend 90% of the distance to the posterior corpus calcareum ( Fig. 5B 3 ). Ventral foramina are situated posteriorly on the centrum and extend 90% of the distance between each corpus calcareum.

The centra of Cardabiodon ricki are classified as round with height equal to width (WAM 96.3.175.1; Siverson 1999: fig. 11.3A). Centra of Cardabiodon ricki are short (among all neoselachians) ranging from 0.3 to 0.51 (ratio of length/ width), but medium in length for lamniforms. Centrum length is comparable to Carcharodon carcharias (0.51), but shorter than in Carcharias taurus (0.55), Ce. maximus (0.61), and I. oxyrhincus (0.65) ( Kozuch and Fitzgerald 1989). The centrum length/width ratio of Cretoxyrhina mantelli ranges from 0.28 (posterior precaudal, FHSM VP-2184) to 0.31 (mid-precaudal, FHSM VP-2187), and up to 0.44 (anterior precaudal, FHSM VP-233) ( Figs. 7 , 8 ). The centra of Cretalamna hattini are shorter than those of Cardabiodon ricki and short for lamniforms ranging from 0.40 to 0.42 (LACM P-128126).

Centra are septate with straight, complete septae as in Carcharodon carcharias ( Fig. 9A ; Kozuch and Fitzgerald 1989: fig. 7; LACM I-35875-1 [5 m TL, 83 mm centrum diameter]). The radial lamellae originate from the focus and are more robust (1.3–1.6 mm thick, WAM 96.4.45.128) than those (1.0– 1.2 mm thickness) from centra of Ce. maximus ,

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10 m TL, 98 mm centrum diameter ( Fig. 9B, C ; LACM I-35593-1). Radial lamellae can bifurcate anteriorly and posteriorly at the corpus calcareum. In lateral view, density of radial lamellae is low with interseptal spaces being 2.9–3.8 times the thickness of the lamellae as in Carcharias taurus Rafinesque, 1810 (see centrum in Kozuch and Fitzgerald 1989: fig. 5) and Hypotodus verticalis (NHMUK OR.12377, OR.38867). Carcharodon carcharias has moderate density for a 5 m long individual with gracile lamellae being 1 mm thick and having interseptal spaces ranging 1.7–1.9 times the thickness of the lamellae ( Fig. 9A ; LACM I-3578-1). In contrast, radial lamellae are gracile and very densely packed in Ar. kopingensis ( Cook et al. 2011; LACM I-128125) and Cretalamna hattini (LACM P-128126; also figured in Shimada 2007: fig. 3D and Siversson et al. 2015: fig. 14). The radial lamellae in Cretoxyrhina mantelli ( Figs. 7 , 8 ; FHSM VP-323, VP-2184, VP-2187; KUVP 55060; DMNH 746C) are gracile and densely packed with interseptal spaces being 1–1.5 times the thickness of the lamellae (1 mm thick; FHSM VP-2184) ( Fig. 8 ). No radial lamellae are present in Ce. maximus ; septae are incomplete and do not extend to the focus ( Fig. 9B 1 ; LACM I-35593-1). No radial lamellae were present in any of the centra of Squalicorax spp. examined KUVP 55190; SDSM 34975, 82067; UWGM NS.1509.07, 1509.34), and all Squalicorax centra, included in this study, were associated with teeth.

The intermedialia, the region between the corpora calcarea, is open (not solid). There are no concentric lamellae in the intermedialia of centra of Cardabiodon ricki (WAM 96.3.175.1, 96.4.45.128), unlike those thin concentric lamellae present in Cretoxyrhina mantelli , figured by Shimada 2008: fig. 7B). The expanded bases of the concentric lamellae can be seen in hemisected view of fig. 7b of Shimada 2008). The radial lamellae of Cretoxyrhina mantelli have densely-spaced, low, longitudinal ridges (?bases of concentric lamellae) on both sides of the lamella (FHSM VP-2184); the radial lamellae of Cardabiodon ricki are smooth. Concentric lamellae are also absent in Ar. kopingensis (LACM P-128125), Cretalamna hattini (LACM P-128126; Siversson et al. 2015), Isurus paucus (LACM I-57284-1, I-57285-1), and I. oxyrinchus (LACM I-39470-2). Concentric lamellae are not visible in Carcharodon carcharias (LACM I-35875- 1, I-42094-1, I-57280-1, I-57281-1, I-57282-1, I-57283-1). Concentric lamellae are present in Ce. maximus (LACM I-35593-1).

No diagonal septa are present around the dorsal and ventral foramina in Cardabiodon ricki , Cretoxyrhina mantelli Figs. 5 , 7 , 8 ), or Cretalamna hattini (LACM P-128126; Siversson et al. 2015). The diagonal septa create an appearance of a network of irregularly situated septa, which can be seen in centra of Ce. maximus ( Fig. 9C 1 ; LACM I-35593-1).

The biconcave surface of the corpus calcareum shows numerous concentric ridges with papillose texture and grooves Fig. 5A 1 , A 2 ). The rim of the corpus calcareum is wide in lateral view. In hemisected view, the rim of the corpus calcareum is overall flat on the lateral side and not greatly curved as seen in Cretalamna hattini (LACM P-128126), Cretoxyrhina mantelli (FHSM VP-2187), Carcharodon carcharias (LACM I-35875-1), but unlike the rounded rim of Ce. maximus (LACM I-35593-1) ( Figs. 7–9 ). In Ce. maximus LACM I-35593-1) the rim curvature is antero- or posteromedial ( Fig. 9B 4 , C 3 ). The corpus calcareum is thick and greatly thickens laterally towards the margin ( Fig. 5B 6 ). In contrast, Ce. maximus has a very thin corpus calcareum at small centrum diameters, but the distal end of the arm of the corpus calcareum thickens in larger sizes ( Fig. 9C 3 ; LACM I-35593-1; Natanson et al. 2008). At the margin of centra of Cardabiodon ricki the corpus calcareum is 8–11% the thickness of the centrum diameter as is that of Ce. maximus 9%; LACM I-35593-1). In contrast, the corpus calcareum has a relatively uniform thickness in centra of Cretoxyrhina mantelli at ~7–8% ( Figs. 7 , 8A–C, E ; FSHM VP-2184, VP-2187; Shimada 2008: fig. 7A), Ar. kopingensis (8%; Cook et al. 2011: fig. 5D), Cretalamna hattini (7%; LACM P-128126; Siversson et al. 2015), Squalicorax spp. (3–5%; KUVP 55190; SDSM 34975, 82067; UWGM NS.1509.07,

1509.34), and Carcharodon carcharias (4–7%; LACM I-35875-1; Kozuch and Fitzgerald 1989: fig. 7).

The thickness of the corpus calcareum in Cardabiodon ricki is especially evident with regard to the length of the centrum. Cardabiodon ricki has a corpus calcareum thickness that is 28% the length of the mid-trunk centrum (WAM 96.3.175.1, 96.4.45.128). When compared to Cardabiodon ricki , the corpus calcareum is much thinner in anterior and mid-trunk precaudal centra of Cretoxyrhina mantelli (10– 16%; anterior precaudal centra AMNH FF 7210; FHSM VP-233, VP-2187; but 23% in posterior precaudal centra FHSM VP-2184), Ar. kopingensis (14%; LACM P-128125), Cretalamna hattini (14%; LACM P-128126; Siversson et al. 2015), Carcharodon carcharias (9–14%; LACM I-35875-1; Kozuch and Fitzgerald 1989: fig. 7), and Lamna nasus (22%, n = 1; Natanson et al. 2002: fig. 3, n = 3) ( Figs. 5 , 7 , 8 ).

Pores (1–2 mm oval foramina) are found on the sides of the centra adjacent to the anterior and posterior corpus calcareum near the dorsal and ventral articular foramina of Cardabiodon ricki (WAM 96.3.175.1, 96.4.45.128; Siverson 1999: fig. 11.2B). Archaeolamna kopingensis (LACM P-128125; Cook et al. 2011: fig. 5B) has round to elongate, subovate pores adjacent to the anterior and posterior corpus calcarea in a continuous pattern. Pores are present on Cretoxyrhina mantelli adjacent to the corpus calcareum but only situated next to the dorsal and ventral articular foramina ( Fig. 8A–C ; FHSM VP-2184). No pores were visible on Cretalamna hattini (LACM P-128126; Siversson et al. 2015), Hypotodus verticalis (NHMUK OR.12377, 38867), or Squalicorax spp. (KUVP 55190; SDSM 34975, 82067; UWGM NS.1509.07, 1509.34; USNM 425665). Very small pores are scattered across the lateral faces of Carcharodon carcharias (LACM I-35875-1) and Ce. maximus (LACM I-35593-1) ( Fig. 9 ). No fine radial canals are visible on the inner surface of the corpus calcareum of centra of Cardabiodon ricki .

The centra of Cardabiodon ricki can be distinguished from those of other lamniforms by a combination of the following characteristics; medium length, round centrum with a very thick corpus calcareum, a corpus calcareum with a flat rim, very robust radial lamellae, radial lamellae that occur in low density, concentric lamellae absent, and small circular or subovate pores concentrated next to each corpus calcareum.

Bands and growth characteristics. — The birth ring may be associated with an angle change on the interior surface of the corpus calcareum of Cardabiodon ricki ( Fig. 5A 2 , B 6 ). There is a crack running through this region but a change in thickness also occurs across the crack to suggest an angle change might be present, but further observations are needed. Cracks often follow the angle change as there is a change in thickness (MGN personal observation). Post birth, the surface of the corpus calcareum has more numerous fine concentric ridges but only robust, papillose ridges are associated with annual rings. In hemisected view, the birth ring consists of a broad darker ring that extends into the intermedialia ( Fig. 5A 2 ).

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The birth ring of Cretoxyrhina mantelli is associated with an angle change on the inner surface of the corpus calcareum, but the outer surface of the corpora calcarea show little difference in surface relief on some centra (FHSM VP-2187; Shimada 2008). In Ar. kopingensis the birth ring is not associated with an angle change in the corpus calcareum and no surface features on the corpus calcareum can be seen due to poor preservation (LACM P-128125).

After birth, the banding pattern in Cardabiodon ricki (WAM 96.4.45.128) usually consists of a light, wide ring, and four dark rings separated by light rings in each band cycle. Three of the dark rings are very thin and occur following a broad light ring. The fourth dark ring is also broad and extends into the region of the intermedialia on the radial plates. The ring starts in a concentric groove, but ends concurrently with a papillose ridge and on the surface of the corpus calcareum ( Fig. 5A 2, B 2 ). The fourth ring is assumed to be an annual mark. Occasionally a second, low papillose

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ridge falls on the white rings between the dark rings. The banding pattern can be seen on both arms of the corpora calcarea. Bands crowd toward the distal part of the arm of the corpus calcareum.

Following birth in Cretoxyrhina mantelli , the banding pattern is relatively simple with broad, dark rings interspersed with lighter coloured rings (FHSM VP-2187, VP-2184; Shimada 2008). Sometimes lighter rings in the banding cycle contain thin or incomplete darker rings but these are considered artefact of some banding cycles ( Shimada 2008). In Ar. kopingensis the banding cycle contains broad dark rings that extend onto the radial plate and are assumed to be annual marks (LACM P-128125; Cook et al. 2011). These dark, annual rings are interspersed with lighter, broad rings to form the complete band.

Age and growth. — The birth rings of Cardabiodon ricki occur at sizes of 5 and 6.6 mm RD, which overlap in RD with those of Cretoxyrhina mantelli (6–11.6 mm RD) ( Figs. 7 , 8 , 10 , 11). The birth ring of Carcharodon carcharias is 9.5 mm RD (LACM I-35875-1). The birth ring RD for Ar. kopingensis (LACM P-128125) is 5.4 mm and is comparable in size to those of Cardabiodon ricki ( Fig. 10 ).

Both specimens of Cardabiodon ricki (WAM 96.4.45.128, 96.3.175.1) have 13 bands, which are assumed to represent years ( Fig. 10 ); other studies have reported bands to represent years ( Natanson et al. 2002, 2006). In contrast, Cretoxyrhina mantelli lived to at least 21 years (bands; FHSM VP-14010). To determine if there was consistency in age along the vertebral column, two centra were aged from the holotype of Cardabiodon ricki and both produced the same age estimates; a precaudal centrum (WAM 96.4.45.128) and a relatively small caudal centrum (WAM 96.4.45.129; Fig. 5C ). The maximum RD of both Cardabiodon ricki precaudal centra ranges from 33–42 mm RD and up to 45 mm RD ( Siverson 1999), which fall within the range of those radial distances of Cretoxyrhina mantelli at the same age (32–47 mm RD) ( Fig. 10 ). Growth tapers off after age 5 in WAM 96.3.175.1 with 86% of its total size attained by age 5. In the holotype (WAM 96.4.45.128), an inflection in growth is not apparent. In both precaudal specimens of Cardabiodon ricki , the growth profile is somewhat to strongly curvilinear ( Fig. 10 ). The inflections in growth of Cretoxyrhina mantelli start to occur at age 4 (58% of total RD) but range up to age 9 (83% of total RD) ( Fig. 10 ). The inflection in growth for Ar. kopingensis (LACM P-128125) occurs at age 5 (69% of total RD).

Confirmation of birth ring size. — An isolated tooth (WAM 13.6.1) from a very young, possibly neonate was used to determine whether the proper ring was identified as the birth ring in Cardabiodon ricki . Lower lateroposterior teeth from three consecutive positions, estimated to include the tooth position of WAM 13.6.1, were plotted with back-calculat- ed sizes from Cardabiodon ricki (WAM 96.4.45.62: lp7?, WAM 96.4.45.88: lp8?, WAM 94.4.45.89: lp9?) ( Fig. 11A). The back-calculated tooth TW for lower lateroposteriors assigned to lp7–9 range from 3.8–4.9 mm TW ( Fig. 11A). This corresponds closely with the estimated 4 mm original TW (3.6 mm as preserved) of WAM 13.6.1.

In comparison, the birth rings of two specimens of Cretoxyrhina mantelli are 4.8:1 (i.e., 21%; FHSM VP-14010) and 4.7:1 (i.e., 21%; FHSM VP-2187) of maximum size at oldest age ( Fig. 10 ). A specimen likely belonging to Cretoxyrhina agassizensis (because of its late Cenomanian age) is 4.4:1 (i.e., 22%; DMNH 746C). The juvenile a2 tooth of Cretoxyrhina agassizensis (WAM 13.6.2) from the basal Haycock Marl is 6.2 mm TW and the largest anterior tooth of this taxon from the same stratum is an incomplete A2 with an estimated TW of 22 mm. This produces a 4:1 ratio for comparable teeth if we use data from Smoky Hill Chalk Cretoxyrhina mantelli (a2’s approximately 15% wider than A2’s) and a 3:1 ratio if we use Cr. vraconensis as template (the A2’s appears to be wider than the a2’s in this taxon; Siverson et al. 2013). Given that the 3–4:1 ratio for isolated teeth is based on no more than a dozen teeth, the ratio between vertebral diameter and the birth ring in large centra should exceed at least 3:1 by some margin, assuming an isometric relationship between anterior tooth width and centrum growth as measured by the diameter.

The sizes of birth rings of Cardabiodon ricki , Cretoxyrhina mantelli , and Ar. kopingensis overlap in diameter with birth rings of six extant lamniforms ( Fig. 11B). In general, birth rings can vary in size by 36% (6.4–10.0 mm RD) in Carcharodon carcharias and up to 45% (3.0– 5.5 mm RD) in L. nasus ( Fig. 11B).

Figures

Fig. 4. Reconstructed lower dentition of Cardabiodon ricki Siverson, 1999 (WAM 96.4.45) from uppermost 10 cm of the Gearle Siltstone (middle Cenomanian), CY Creek, Giralia Range, Western Australia, depicting mirror images of left anterior teeth on the right side.

Fig. 5. Centra of Cardabiodon ricki Siverson, 1999 from uppermost 10 cm of the Gearle Siltstone (middle Cenomanian), CY Creek, Giralia Range, Western Australia. A. Precaudal centrum, WAM 96.4.45.128. Face of the corpus calcareum (A1) showing line of section (black line) and transect with points of measurement (white line and circles), large filled circle represents focus, left half of the section centrum correseponds to A2, right half of the centrum corresponds to A3. “Hemisected” view of centrum (A2) showing the number of bands, angle of the section does not intersect the focus as it was missing from the originally incomplete centrum, the point of the focus occurs in -z space (behind the plain of the page). Opposing view showing focus (A3). B. Precaudal centrum, WAM 96.3.175.1. Anterior view of corpus calcareum with surface removed to show bands (B1); centrum (B2); dorsal view of centrum B3), ovals show outline and position of articular foramina for the neural arch (anterior to left); lateral view of centrum (B4) oval outlines rib articular foramen (anterior to left); hemisected section of centrum (B5) (anterior to left); enlarged, hemisected view (B6) showing bands. C. Caudal centrum, WAM 96.4.45.110 (oblique angle), anterior view showing birth ring.

Fig. 6. Centrum size profiles of Cardabiodon ricki, Cretoxyrhina mantelli, Cretalamna hattini, Archaeolamna kopingensis, and Squalicorax sp. Centrum diameter of Cardabiodon ricki (WAM 96.4.45.108) compared to those of other lamniforms: Ar. kopingensis (LACM P-128125), Cretoxyrhina mantelli (FHSM VP-323, VP-2187), Cretalamna hattini (LACM P-128126), and Squalicorax (LACM P-120090; USNM 425665). Centrum sizes for Ar. kopingensis, Cretoxyrhina mantelli, and Squalicorax spp. are taken from Cook et al. (2011).

Fig. 3. Isolated, small juvenile teeth of Cardabiodon ricki Siverson, 1999 (WAM 13.6.1: lp7–9?) (A) and Cretoxyrhina agassizensis (Underwood and Cumbaa, 2010) (WAM 13.6.2: a2?) (B) from the basal (0.1 m) of the Haycock Marl, Pillawarra Plateau, Western Australia, late Cenomanian or early Turonian. In labial (A1, A2) and lingual (B1, B2) views.

Fig. 7. Centra of Cretoxyrhina spp. A, B. Cretoxyrhina mantelli (Agassiz, 1843), late Coniacian–middle Santonian, Smoky Hill Chalk, Niobrara Chalk, Gove County, Kansas, USA. A. FHSM VP-323. B. FHSM VP-2187, articulated centra from various positions in the vertebral column; v1–14 (B1), v1 = occipital centrum, order corresponds to Fig. 6; v62–66 (B2); v67–75 (B3); v86–93 (B4); v94–104 (B5); v129–139 (B6); v183–193 (B7); v194–208 (B8); v 209–227 (B9). C. Centrum in transverse section through about inner margin of the corpus calcareum of Cretoxyrhina mantelli, NHMUK OR.25939, White Chalk Formation (?), near Sussex, UK; arrows indicate articular foramina for neural and ribs or haemal arches (see also Woodward 1912: pl. 43: 14). D. Centrum of Cretoxyrhina sp. (probably Cretoxyrhina agassizensis), DMNH 746C, Eagle Ford Group, Cenomanian, Tarrent County, Texas, USA; view of face (D1) showing focus and 15 bands (black arrows) after the birth ring; tracing of left lateral view of centrum (D2). E. Centra of Cretoxyrhina sp. (probably Cretoxyrhina agassizensis), NHMUK OR.49015, Cenomanian–Turonian, near Kent (?), UK.

Fig. 8. Five posterior precaudal(?) centra of Cretoxyrhina mantelli Agassiz, 1843, late Coniacian–early Santonian, Smoky Hill Chalk of the Niobrara Chalk, Kansas, USA. A–C. Centra, FHSM VP-2184a (A), FHSM VP-2184b (B), and FHSM VP-2184c (C), in anterior or posterior (A 1 –C 1), left lateral (A 2 –C 2), dorsal (A 3 –C 3), and ventral (A 4 –C 4) views. D. Centrum, FHSM VP-2184d, in transverse section showing radial lamellae and dorsal and ventral articular foramina; in anterior and posterior (D , D ) views. E. Centrum, FHSM VP-2184e, in hemisected view showing 12 bands (arrows).

Fig. 9. Centra from extant Carcharodon carcharias Linnaeus, 1758 (A) and Cetorhinus maximus Gunnerus, 1765 (B, C). A. Centrum, LACM I-35875- 1, in anterior (A 1), left lateral (A 2), posterior (A 3), dorsal (A 4), and ventral (A 5) views. B. Partial centrum (LACM I-35593-1a) in transverse section (B 1) posterior (B 2), left lateral (B 3), and dorsal (B 4) views. C. Partial centrum (LACM I-35593-1b) in left lateral (C 1), ventral (C 2), and one-half hemi-section (C ) views.

Fig. 1. Early Late Cretaceous map (90 Ma; PLATES Program 2009) showing locations of fossil localities (late Cenomanian to middle Turonian) yielding Cardabiodon spp. (see Cook et al. 2010). UALVP 49430 from Canada is likely a transitional morphotype between Cardabiodon ricki and Cardabiodon venator.

Fig. 2. Schematic drawing of a hypothetical shark centrum in hemisected view showing potential criteria used for age determination.

Fig. 10. Centrum growth profiles and size profiles of Cardabiodon ricki ( blue lines), Cretoxyrhina mantelli, Cretoxyrhina agassizensis, and Archaeolamna kopingensis. Centrum radial distance is distance from focus toward the margin along a transverse plane at the anterior or posterior ends of the centrum (note: no line is figured between birth ring and band 1 in A. kopingensis because of damage in corpus calcareum where distance between them was extrapolated from size of retained fragments of corpus calcareum [see Cook et al. 2011]; filled symbols represent presumed annual rings); specimens depicted as “Cretoxyrhina spp.” are those centra not preserved with teeth but have a matching morphology to those found with teeth; the growth profile of WAM 96.4.45.128 was measured from the face of the corpus calcareum (Fig. 5A 1) and does not reflect the exact proportions of growth recorded in the “hemisected” view of the centrum in Fig. 5 A as the angle of the section does not intersect the focus.