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Home , Anacoracidae, Cretalamna, Cretoxyrhina, Kristianstad Basin, Mitsukurinidae, Pseudocorax

Lucas, S. G. and Sullivan, R.M., eds., 2006, Late from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 35. 185 CAUDAL FIN SKELETON OF THE LAMNIFORM , MANTELLI, FROM THE NIOBRARA CHALK OF

KENSHU SHIMADA1, STEPHEN L. CUMBAA2, AND DEANNE VAN ROOYEN3

1Environmental Science Program and Department of Biological Sciences, DePaul University, 2325 North Clifton Avenue, Chicago, Illinois 60614; and Sternberg Museum of Natural History, Fort Hays State University, 3000 Sternberg Drive, Hays, Kansas 67601; 2Paleobiology, Canadian Museum of Nature, P.O. Box 3443, Station D, Ottawa, Ontario K1P 6P4, Canada; 3Department of Earth Sciences, Carleton University, 2240 Herzberg Laboratories, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada.

Abstract—The caudal fin morphology of the Late Cretaceous lamniform shark, Cretoxyrhina mantelli (Agassiz), was previously inferred from scale morphology, which suggested that it was capable of fast swimming. A specimen from the Niobrara Chalk of western Kansas is described here and offers new insights into the morphology of the caudal fin of the taxon. The specimen preserves the posterior half of the vertebral column and a series of hypochordal rays. These skeletal elements exhibit features suggesting that C. mantelli had a lunate tail and a caudal peduncle with a lateral fluke. The specimen also supports the idea that the body form of C. mantelli resembled that of the extant white shark, (Linneaus). Given a total vertebral count in Cretoxyrhina mantelli of about 230, this specimen suggests that the transition between precaudal and caudal vertebrae was somewhere between the 140th and 160th vertebrae. The estimated total body length of the specimen described here ranges from 640 cm to 700 cm, marking the largest C. mantelli individual estimated to date. New skeletal data from the specimen further supports the view that C. mantelli was an active shark capable of fast swimming.

INTRODUCTION insights into the shape of the shark’s tail. The purpose of this paper is 1) to describe the morphology of the specimen, and 2) to discuss the caudal fin Cretoxyrhina mantelli (Agassiz) was a Late Cretaceous lamniform morphology of C. mantelli and its paleoecological significance. For com- shark that lived in – seas worldwide, including the parative purposes, specimens in the following institutions are referred of North America (e.g., Cappetta, 1987; Siverson, to in this paper: Sternberg Museum of Natural History, Fort Hays State 1992, 1996; Shimada, 1997d). The is represented chiefly by its University (FHSM), Hays, Kansas; and the paleontology collec- teeth, but some reasonably complete skeletons of the species are known tion of the University of Kansas Museum of Natural History (KUVP), from the late – portion of the Smoky Hill Chalk Mem- Lawrence. ber of the Niobrara Chalk in western Kansas (Shimada, 1997b). Those skeletal remains suggest that large individuals of C. mantelli measured about SYSTEMATIC PALEONTOLOGY 5 to 6 m in total length and possibly had a body form similar to the modern great shark, Carcharodon carcharias (Linnaeus) (Shimada, 1997b). The Class fossil record demonstrates that Cretoxyrhina mantelli fed on large marine Subclass vertebrates (e.g., , sea , , and plesiosaurs: Shimada, Order Berg, 1958 1997c; Shimada and Everhart, 2004; Shimada and Hooks, 2004; Everhart, Family Cretoxyrhinidae Glikman, 1958 2004, 2005a) and possibly scavenged “bloat-and-float” carcasses of fully terrestrial vertebrates (e.g., nodosaurid : Everhart and Hamm, Cretoxyrhina Glikman, 1958 2005). Cretoxyrhina mantelli (Agassiz, 1843) Despite the wealth of information about the paleobiology of Cretoxyrhina mantelli (e.g., Shimada, 1997a, 1997b, 1997c), there are Material—CMN 40906 (Figs. 1–5), a string of caudal and poste- rior precaudal vertebrae with hypochordal rays and placoid scales. still many unresolved questions. The morphology of its caudal fin is one such gap in our knowledge. The previously suggested morphology, and the Horizon and locality—The specimen was collected by G. F. Sternberg from the Niobrara Chalk (Upper Cretaceous: see Hattin, 1982) estimated starting point of the caudal fin in C. mantelli (Shimada, 1997b), were based on a series of assumptions. Shimada (1997b) demonstrated in western Kansas. It was sold to the Geological Survey of Canada, from which the museum originated, in 1912. that C. mantelli had keeled placoid scales with an average interkeel dis- tance of approximately 45 microns. Because this interkeel distance is com- Because exact biostratigraphic data were not available to constrain the age of the specimen within the Niobrara Chalk, chalk samples were parable to that in scales of some extant fast-swimming , Shimada (1997b) inferred that C. mantelli was also capable of fast swimming. This taken from the matrix for stratigraphically diagnostic foraminiferans. Our result shows that four taxa dominate the assemblage. Heterohelix globulosa evidence, combined with the fact that C. mantelli had a conical head, led Shimada (1997b) to consider that the species had a stout fusiform body (Ehrenberg), with a Campanian – range, is the most abun- dant. The other key taxa are: Archeoglobigerina cretacea (d’Orbigny), with a lunate caudal fin for efficient hydrodynamic propulsion. Given that the fossil species had a total vertebral count of approximately 230, Shimada with a range from middle Coniacian–early Maastrichtian; Rugoglobigerina rugosa (Plummer), known from the early Campanian; and Whiteinella (1997b) suggested that the caudal fin of C. mantelli could have begun at about 133rd vertebra, on the basis of comparisons with some extant fast- centennialensis Frerichs, which occurs in late Santonian–early Campanian strata (Pessagno, 1967; Frerichs et al., 1975; Frerichs, 1979). The pres- swimming lamniform sharks with lunate tail fins (e.g., lamnids: Cuvier, Rafinesque, and Carcharodon Smith). ence of R. rugosa, which makes up about 10% of the individuals in our sample, strongly suggests that the Cretoxyrhina specimen came to rest on The Canadian Museum of Nature (CMN) in Ottawa, Ontario, houses a putative Cretoxyrhina mantelli specimen, CMN 40906, which consists the chalky ocean bottom in the early Campanian. The shark specimen is thus from the upper part of the Smoky Hill Chalk. If so, whereas C. mantelli of a vertebral column and some additional skeletal elements (Fig. 1). CMN 40906 is noteworthy because of its large size and features that provide new is known from early Campanian deposits (e.g., Siverson, 1992), CMN 186

FIGURE 1. Photograph of CMN 40906, string of vertebrae with hypochordal rays of Cretoxyrhina mantelli (Agassiz) (anterior to the left; scale bar = 30 cm).

FIGURE 2. Line drawing of CMN 40906 (cf. Fig. 1), string of vertebrae (“v”) with hypochordal rays (hcr) of Cretoxyrhina mantelli (Agassiz) (anterior to the left; scale bar = 30 cm).

40906 represents the youngest Cretoxyrhina specimen documented thus far from the Smoky Hill Chalk of Kansas (see Stewart, 1990; Everhart, 2005b, table 13.1). It should be noted that museum records indicate that the specimen was found in Gove County, Kansas, but strata from the lower Campanian (the uppermost Niobrara Chalk) are not known to occur there. Other fossil specimens purchased by the museum from the Sternberg family at the same time list G. F. Sternberg as the collector, and Logan County as the source. Because outcrops with lower Campanian strata do occur just west of Gove County in Logan County (Hattin, 1982), perhaps the collection data are incorrect. Description—A total of 109 vertebral centra are physically preserved in the specimen (Fig. 1). The anteriormost ninety-five of these are clearly in anatomical sequence and are in a good state of preservation. We refer to these as “v1” through “v95”, counting sequentially from the anteriormost centrum in the specimen (Fig. 2). The v-numbers are placed in quotations to highlight the fact that they are artificial assignments. There are impres- sions of four vertebrae near “v95” which are otherwise missing. Fourteen smaller vertebrae, generally in poor condition, are on the slab, but are largely FIGURE 3. Close-up view of vertebral centra (“v23”-“v25”: see Fig. 2) in CMN disarticulated, and have not been assigned v-numbers. If the four missing 40906 (scale bar = 2 cm). vertebrae and the 14 smaller vertebrae are counted, CMN 40906 consists 187

FIGURE 4. Close-up view of putative caudal fin base, showing connection between vertebral column and hypochordal rays in CMN 40906 (scale bar = 10 cm; cf. Figs. 1, 2).

FIGURE 5. Placoid scales (four examples) of Cretoxyrhina mantelli (Agassiz) from CMN 40906 (scale bar = 50 micronsm). Sample locations are relative to vertebral positions in Figure 2. A, Scale from dorsal to “v24”: top, apical view (anterior to the top); bottom, anterior view. B, Scale from above, or ventral to “v66”: left, oblique view (anterior to the top left); right ,anterior view. C, Scale location same as A: lateral view (anterior to the left). D, Scale location same as B: apical view (anterior to the right). 188

FIGURE 6. Example of articulated vertebrae of Cretoxyrhina mantelli (Agassiz) (anterior to the left; scale bar = 10 cm; v 73–v82 in FHSM VP-2187: see Shimada, 1997b). A, vertebrae in right(?) lateral view (note that this surface was against ocean floor when the shark skeleton was buried); B, vertebrae in dorsal(?) view (note post- burial distortion that resulted in lateral flattening of vertebrae). of a total of 113 vertebrae. the tail. The centra (Fig. 3) are amphicoelous and asterospondylic with nu- A few patches of articulated placoid scales and many disarticulated merous concentric lamellae around the primary double-cone calcification scales were found in the chalk matrix surrounding the specimen (Fig. 5). (see Welton and Farish, 1993). The centra are well calcified, and the “double- The scales are of two types. The most common (Figs. 5A, 5C) mea- cones” are thick and are supported by many radial plates. A pair of sures approximately 150–200 microns in maximum dimension, and con- circular pits for the basidorsal and basiventral is observed on op- sists of a large, keeled and fluted crown and a somewhat smaller root. The posite sides of the periphery of each centrum. The pair with a narrower crown has an oval apical surface and generally shows six to eight parallel, inter-pit distance in each centrum is assumed to be the side of basidorsal U-shaped grooves oriented longitudinally, which emerge from the rounded cartilages (see Shimada, 1997b), and thus representing the dorsal side of anterior margin. The posterior crown margin is thin and overlaps with pos- the shark. teriorly located scales. The grooves are bounded on each side by a keel, Most vertebrae are articulated, and the vertebral column shows a with an average interkeel distance of 25–30 microns. The junction be- dorsal bend at about “v42” at an angle of approximately 45o (Fig. 2). The tween the crown and root is constricted. The root base is flat and diamond- anteriormost centra in the specimen are circular and measure approximately shaped with one foramen at its center. 88 mm in diameter and 18 mm in anteroposterior length (note that “v1” The second type was represented by only two scales in our samples and “v2” are heavily damaged: Appendix 1). Centra towards the posterior (Figs. 5B, 5D). These scales are more massive, with a prominent, rounded, end of the specimen are slightly elongated dorsoventrally. Many vertebrae bulbous root perforated around the top by several foramina. Root to crown suffer post-burial distortion (see below for further discussion), but they length exceeds 400 microns. The crown is relatively flat, and sub-circular generally decrease in their diameter gradually at a rate of 0–6 mm per five to rounded quadrilateral in shape, with a greatest dimension of approxi- vertebrae from “v3” to “v35” and from “v40” to “v95”, except between mately 325 microns in the larger specimen. The crown ornamentation con- “v35” and “v40” with a decreasing rate of 15 mm. The last “articulated” sists of sinuous grooves and ridges in one specimen; the other, more worn vertebral centrum has a diameter of approximately 19 mm. Some verte- on top, appears more similar to the scales described above. The crown brae may be missing from the tip of the tail. The exact number of vertebrae edges appear somewhat worn and rounded in both specimens. missing from the caudal tip is unknown, but it cannot be more than a very Taphonomic and taxonomic remarks—A number of vertebrate few as the smallest of the disarticulated vertebrae has a centrum diameter specimens from the Smoky Hill Chalk of Kansas in various museum col- of about 6 mm. lections consist of multiple individuals that were artificially assembled for A tabular piece of calcified cartilage extends ventrally from nearly aesthetic value (e.g., Bardack, 1965). In CMN 40906 described here, some each vertebral centrum from “v42” to “v65” (i.e., a total of 23–24 pieces: vertebrae are disarticulated and slightly displaced. However, we are confi- Figs. 2, 4). These are interpreted to be hypochordal rays (see Compagno, dent that all skeletal components in CMN 40906 belong to one shark indi- 1999). The anteriormost ray measures 29 mm in length and 10 mm in vidual, because 1) each pair of adjacent vertebrae are either articulated or width. The length gradually increases posteriorly at about “v51”, where nearly identical in their vertebral diameter, and 2) the entire vertebral col- the piece measures 150 mm in length and 15 mm in width (although the umn along with the hypochordal rays is partially to completely embedded widest is 25 mm at “v49”), and then gradually decreases towards the tip of in the original chalk matrix. The entire ventral surface of the specimen is 189 embedded in original matrix, as are “v31-35” and “v51-97.” There is plas- ter fill along the dorsal edge of “v1-30” and “v36-50”, but as these verte- brae remain anchored in chalk (except for two or three between “v20” and “v25” which are loose, but have impressions in the chalk), there is no indi- cation that the fill involved any artificial movement or substitution of verte- brae by the preparators of the specimen. Whereas the vertebral diameter generally decreases from the anteri- orly located vertebrae towards the posteriorly located vertebrae, we note that certain sections of the vertebral column, such as “v4”–“v8”, “v46”– “v62”, and “v70”–“v83”, show some irregularities in the maximum verte- bral diameters (note that such measurements were excluded: see Appendix 1). The irregularities are not due to artificial causes (e.g., artificial arrange- ment of vertebrae) but are due to post-burial distortion of vertebrae through fossilization. Figure 6 shows a typical example of taphonomically flattened articulated Cretoxyrhina vertebrae from the Smoky Hill Chalk of Kansas. The effect of flattening of vertebrae is that the vertebral diameter of one axis tends to extend, whereas the vertebral diameter of the other axis per- pendicular to it tends to shorten (e.g., see middle section of vertebral string in Fig. 6). Therefore, except for some slightly displaced vertebrae, the ar- rangement of vertebrae in CMN 40906 is determined to reflect the original sequence in the shark individual. The of extinct sharks generally depends on their dental morphology. Thus, the identification of fossil shark specimens not found in association with teeth is generally difficult. Nevertheless, the calcifica- tion pattern characterized by many radial cartilage plates (i.e., platy pri- mary exochordal radii: Compagno, 1990) is a strong indication that CMN 40906 belongs to the order Lamniformes. From the Smoky Hill Chalk of Kansas, the following lamniform taxa are known to date: raphiodon (Agassiz), Johnlongia sp., laevis (Leriche), falcatus (Agassiz), S. kaupi (Agassiz), S. pristodontus (Agassiz), S. volgensis (Glikman in Glikman and Shvazhaite), appendiculata (Agassiz), and Cretoxyrhina mantelli (e.g., Hamm and Shimada, 2002; Hamm et al., 2003; Beeson and Shimada, 2004; Shimada et al., 2004; Shimada, 2005b, Shimada and Cicimurri, 2005). Where col- lecting bias towards large vertebrates appears to exist in the fossil record of the Niobrara vertebrates (Hamm and Shimada, 2002), the largest lamniform shark known from the Smoky Hill Chalk is C. mantelli (see Hamm et al., 2003). Based on comparisons with other C. mantelli specimens from the Smoky Hill Chalk of Kansas (e.g., FHSM VP-323, FHSM VP-2184, FHSM VP-2187, KUVP 247, and KUVP 69102), we note that the morphology (e.g., the thickness of “double-cone” calcification and the organization of radial cartilage plates) and general size of the vertebrae in CMN 40906 described here (e.g., Figs. 1, 3, 4) are identical to centra in those C. mantelli specimens that are associated with teeth (e.g., Fig. 6). Therefore, we are confident that, although CMN 40906 lacks teeth, it is a specimen of Cretoxyrhina mantelli. Shimada (1997b) noted that the average interkeel distance on the crown of scales taken at the caudal region in another Cretoxyrhina mantelli specimen (FHSM VP-2187) from the Smoky Hill Chalk of Kansas was 50.5 microns (note that, at other parts in the specimen, the smallest mean interkeel distance recorded was 30 microns: Shimada, 1994, table 9). This value is much higher than the average interkeel distance in CMN 40906 (i.e., 25–30 ì m), but we note that the scale morphology in CMN 40906 is consistent overall with “Type A” scales in FHSM VP-2187 (see Shimada, 1997b). Where sharks generally show large intraindividual variation in scale morphology (e.g., Welton and Farish, 1993, fig. 20), the discrepancy in interkeel distance values may be due to the fact that the sample size of scales taken from FHSM VP-2187 (particularly at the caudal region) and CMN 40906 was too small to see the possible overlap in interval ranges. DISCUSSION FIGURE 7. Examples of caudal fin (outline and skeleton) in selected extant sharks (anterior to the left; not to scale). A, Isurus Rafinesque (Lamniformes: after Garman, The outline of the caudal fin is not preserved in CMN 40906. How- 1913, pl. 63, fig. 5); B, Mustelus Link (: after Mivart, 1879, pl. ever, the organization of preserved hypochordal rays with respect to the LXXIV, fig. 6); C, Squalus Linnaeus (: after Mivart, 1879, pl. LXXVII, preserved vertebral column (Fig. 4) offers insights into the tail morphology fig. 3). of Cretoxyrhina mantelli. CMN 40906 shows that the anteriormost and 190

FIGURE 8. Tentative skeletal reconstruction of 6-m-long Cretoxyrhina mantelli (Agassiz) based on available fossil record (Shimada, 1997b; this study). Solid lines = known parts; broken lines = inferential parts. preserved posteriormost hypochordal rays are short, whereas the rays be- maximum possible angle observed in extant sharks (see Thomson, 1976). tween them are markedly elongate. In addition, the base of the anteriormost Therefore, CMN 40906 further strengthens the idea (Shimada, 1997b) hypochordal rays in the specimen occurs immediately anterior to the sharp that the body form of Cretoxyrhina mantelli (Fig. 8) resembled that of bend (at an angle of ca. 45Њ) that is observed in the vertebral column. If one extant lamnids, including the white shark, Carcharodon carcharias. We considers the sharp bend at face value as a dorsally directed bend of the assume that Cretoxyrhina mantelli also had a caudal peduncle with a lat- vertebral column that constitutes the axis of a tail, this skeletal organization eral fluke. is remarkably similar to that of extant sharks with a high aspect ratio: i.e., a Quantitative studies of vertebral dimensions in modern sharks are lunate (symmetrical) tail with large dorsal and ventral lobes (Fig. 7A). rare. However, inspection of published illustrations of caudal fins of extant Thomson and Simanek (1977, table 3) listed Rhincodon Smith fast swimming lamniform sharks with lunate tails (e.g., Lamna in Mivart, (Orectolobiformes), Cetorhinus Blainville, Lamna, Isurus, and 1879, pl. LXXV, fig. 1; Isurus in Garman, 1913, pl. 63, fig. 5: e.g., Fig. Carcharodon (Lamniformes) as best representatives of this type of shark, 7A) shows that a marked reduction in vertebral size is present at the with the caudal portion of the vertebral column bent at an angle of ca. precaudal-caudal transition. There are two specimens of Cretoxyrhina =30Њ. The caudal fin of other extant sharks is strongly heterocercal: i.e., an mantelli that preserve a series of vertebrae extending near the terminal asymmetrical tail with a much smaller ventral lobe compared to the dorsal end: FHSM VP-2187 and KUVP 69102. A re-examination of “vertebral one (Thomson and Simanek, 1977). In these sharks, the vertebral column diameters” in the posterior half of the vertebral column in these specimens shows a weak bend or virtually no bend, and the length of the hypochordal (i.e., post-v110: Appendix 2) reveals that a marked decrease in the diam- rays is more or less uniform across the tail (Figs. 7B, 7C). Therefore, CMN eter between v140 and v145 in FHSM VP-2187 (i.e., 6 mm drop in that 40906 supports the hypothesis that Cretoxyrhina mantelli had a lunate tail interval as opposed to 0–4 mm per drop every six vertebrae) and between (Fig. 8). It is noteworthy that, because Rhincodon is not a lamniform (Shirai, v155 and v160 in KUVP 69102 (i.e., 8 mm drop in that interval as op- 1996), and because C. mantelli does not share an immediate common an- posed to 0–4 mm drop per every six vertebrae where distortion is mini- cestry with Cetorhinus, Lamna, Isurus, or Carcharodon (Shimada, 2005a), mal). Therefore, we here suggest that the caudal fin of C. mantelli possibly the similarity in caudal fin morphology between Cretoxyrhina mantelli occurred at an approximate range of v140–v160. and these extant sharks is interpreted to be a homoplasy due to convergent If one assumes that the range of v155–v160, which would give a evolution. However, we note that the caudal fin of C. mantelli possibly had conservative caudal fin size, is equivalent to that of “v35”–“v40” in CMN a wider angle between the upper and lower lobes and a slightly shorter 40906 (where a marked decrease in vertebral size is observed: see above), lower lobe (Fig. 8) compared to the caudal fin of those extant sharks (e.g., the total vertebral count of the shark individual (CMN 40906) was at least Fig. 7A), because the hypochordal rays in CMN 40906 are largely directed 216. The number, 216, corresponds remarkably well to the estimated total ventrally (Figs. 2, 4; as opposed to ventroposteriorly in those extant sharks). vertebral count of Cretoxyrhina mantelli, 230 (see Shimada, 1997b), by We also note that, because the posteriorly located hypochordal rays appear considering the probable number of missing terminal vertebrae (i.e., 10– to be thinner and shorter as compared to those in Rhincodon, Cetorhinus, 25 vertebrae: see above). Lamna, Isurus, or Carcharodon, the lobes of the lunate tail in Cretoxyrhina The largest measurable vertebra in CMN 40906 is “v3”, which has mantelli could have been slightly narrower than the lobes in those extant a diameter of 88 mm. If “v35” is assumed to be v140 in life, “v3” would sharks. then represent v108. In FHSM VP-2187, which is conservatively estimated Thomson and Simanek (1977) found that extant sharks with a het- to be 500 cm TL, the diameter of v108 is 69 mm (Shimada, 1994, table 1). erocercal (Ն “vertebral bent”) angle of ca. Ն30Њ, not only have a well- If one assumes that the vertebral diameter in CMN 40906 has the same developed ventral hypochordal lobe, but also a deep fusiform body with a size relation to the TL as the relationships between the diameter and TL in conical head and a caudal peduncle bearing the lateral fluke. Thomson and FHSM VP-2187, CMN 40906 is 128% of FHSM VP-2187. This suggests Simanek (1977) characterized such sharks as “fast swimming pelagic that the shark individual represented by CMN 40906 was possibly 640 cm sharks,” typified by extant lamnids, such as the mako and white sharks. TL. Whereas this assumption of “v35” representing v140 gives a conser- The vertebral bend in CMN 40906 is about 45Њ, which approximates the vative TL estimate for CMN 40906, one may assume “v35” to be v155 for 191 a less conservative estimate, and in this case, “v3” would represent v123 in mosasaurs, is energetically costly and requires efficient swimming capabil- life. The diameter of v123 in FHSM VP-2187 is 63 mm (Shimada, 1994, ity. Thus, as suggested by Shimada (1997c), it is likely that C. mantelli was table 1). Therefore, CMN 40906 is 140% of FHSM VP-2187, suggesting an active shark capable of fast swimming. Such information is important in that the shark could have measured 700 cm TL. The range of 640–700 cm understanding the paleoecological dynamics of the Cretaceous seas. TL for CMN 40906 represents the largest Cretoxyrhina mantelli individual estimated to date (cf. Shimada, 1997b). ACKNOWLEDGMENTS The caudal fin is the primary locomotor structure in sharks. Al- We thank M. Feuerstack and C. Kennedy (CMN) for assistance with though functional analysis of caudal fins is far from complete even for the specimen, and co-op students H. Bernatchez and M. Brière from l’École living sharks (for review, see Lauder, 2000; Lingham-Soliar, 2005), ex- secondaire de Casselman for their help in locating isolated denticles and amination of caudal fin morphology in extinct sharks is important because scale patches for study. A. Murray (CMN) took the SEM and overall speci- it gives insights into their swimming capability, which in turn, as noted by men photos. We thank M. J. Everhart (FHSM) for his discussion on the Motani (2002), has implications to behavior, physiology, and other aspects Niobrara stratigraphy. The senior author thanks the following present and of their biology. The exact outline of the body and tail of Cretoxyrhina past FHSM and KUVP associates for allowing us access to comparative mantelli (Fig. 8) remains inferential at the present time. However, it is Cretoxyrhina specimens in their care: J. Chorn, C. Fielitz, D. Miao, H.-P. noteworthy that the notion of C. mantelli as a “fast-swimming shark,” Schultze (KUVP), and R. J. Zakrzewski (FHSM). Comments made on supported here, agrees well with the inferred feeding behavior of the taxon earlier drafts by D. J. Ward (Kent, United Kingdom) and M. D. Gottfried based on taphonomic evidence. In particular, a vertebra speci- (Michigan State University) as well as reviews by J. I. Kirkland (Utah Geo- men from Kansas shows signs of healing over an embedded logical Survey) and D. R. Schwimmer (Columbus State University) greatly Cretoxyrhina tooth, suggesting the post-bite survival of the mosasaur indi- improved the quality of this manuscript. vidual (Shimada, 1997c). Biting large, presumably active vertebrates, like

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APPENDIX 1.Approximate diameter (in millimeters) of vertebral centra in CMN APPENDIX 2.Approximate diameter (in millimeters) of vertebral centra in two nearly 40906. Dash = vertebral centrum with severe damage or distortion. complete skeletons of Cretoxyrhina mantelli (Agassiz) (data based on Shimada, 1994, table 1). Value in parentheses = estimated value from adjacent centra; value in brackets = unreliable measurements due to severe distortion of centra.