Abstract: The taxonomic origin of the white shark, Carcharodon , is a highly debated subject. New fossil evidence presented in this study suggests that the genus is derived from the broad‐toothed ‘mako’, Carcharodon ( Cosmopolitodus ) hastalis , and includes the new species C . hubbelli sp. nov. – a taxon that demonstrates a transition between C . hastalis and Carcharodon carcharias . Specimens from the Pisco Formation clearly demonstrate an evolutionary mosaic of characters of both recent C. carcharias and fossil C. hastalis . Characters diagnostic to C. carcharias include the presence tooth serrations and a symmetrical first upper anterior tooth that is the largest in the tooth row, while those indicative of C. hastalis include a mesially slanted third anterior (intermediate) tooth. We also provide a recalibration of critical fossil horizons within the Pisco Formation, Peru using zircon U‐Pb dating and strontium‐ratio isotopic analysis. The recalibration of the absolute dates suggests that Carcharodon hubbelli sp. nov. is Late Miocene (6–8 Ma) in age. This research revises and elucidates lamnid shark evolution based on the calibration of the Neogene Pisco Formation.

Methods and materials Numerous studies indicate the Miocene Epoch was characterized by rapidly increasing 87Sr/86Sr in the global ocean; therefore, it is especially amenable to dating and correlating marine sediments using strontium isotope chemostratigraphy (Hodell et al. 1991; Miller et al. 1991, Hodell and Woodruff 1994, Oslick et al. 1994, Miller and Sugarman 1995, Martin et al. 1999, McArthur et al. 2001). We analysed three fossil marine mollusc shells from each of five localities to determine the ratio of 87Sr/86Sr in the shell calcium carbonate. When compared with the global seawater reference curve, these data allow us to estimate the age of the fossil molluscs for each locality (Table 1). Table 1. Strontium chemostratigraphic analyses of fossil marine mollusc shells from the Pisco Formation. Fossil Horizon Mean 87Sr/86Sr Age estimate (Ma) 95% CI (Ma) El Jahuay 0.7089424 7.46 9.03–6.51 Montemar 0.7089468 7.30 8.70–6.45 Sud Sacaco (West) 0.7089659 6.59 10.77–2.50 Sud Sacaco (West) 0.7089978 5.93 6.35–5.47 Sacaco 0.7090005 5.89 6.76–4.86 For isotopic analyses, we first ground off a portion of the surface layer of each shell specimen to reduce possible contamination. Areas showing chalkiness or other signs of diagenetic alteration were avoided. Approximately 0.01–0.03 g of aragonite or low‐magnesium calcite powder was recovered from each fossil sample. The powdered samples were dissolved in 100 μl of 3.5 N HNO 3 and then loaded onto cation exchange columns packed with strontium‐selective crown ether resin (Eichrom Technologies, Inc., Lisle, IL, USA) to separate Sr from other ions (Pin and Bassin 1992). Sr isotope analyses were performed on a Micromass Sector 54 thermal ionization mass spectrometer equipped with seven Faraday collectors and one Daly detector in the Department of Geological Sciences, University of Florida. Sr was loaded onto oxidized tungsten single filaments and run in triple collector dynamic mode. Data were acquired at a beam intensity of about 1.5 V for 88Sr, with corrections for instrumental discrimination made assuming 86Sr/88Sr = 0.1194. Errors in measured 87Sr/86Sr are better than ±0.00002 (2σ), based on long‐term reproducibility of NIST 987 (87Sr/86Sr = 0.71024). Age estimates were determined using the Miocene portion of Look‐Up Table Version 4:08/03 associated with the strontium isotopic age model of McArthur et al. (2001). Zircons were extracted from samples using standard crushing, density separation and magnetic separation techniques. The zircons were hand picked, mounted in epoxy plugs along with the reference zircon FC‐1 (Paces and Miller 1993) and analysed using laser ablation multi‐collector inductively coupled plasma mass spectrometry (LA‐MC‐ICP‐MS). We used a Nu Plasma mass spectrometer fitted with a U‐Pb collector array at the Department of Geological Sciences, University of Florida. 238U and 235U abundances were measured on Faraday collectors and 207Pb, 206Pb and 204Pb abundances on ion counters. The Nu Plasma mass spectrometer is coupled with a New Wave 213 nm ultraviolet laser for ablating 30–60 μm spots within zircon grains. Laser ablation was carried out in the presence of a helium carrier gas, which was mixed with argon gas just prior to introduction to the plasma torch. Isotopic data were acquired during the analyses using Time Resolved Analysis software from Nu Instruments. Before the ablation of each zircon, a 30 s peak zero was determined on the blank He and Ar gases with closed laser shutter. This zero was used for online correction for isobaric interferences, particularly from 204Hg. Following blank acquisitions, individual zircons underwent ablation and analysis for c. 30–60 s. The analyses of unknown zircons were bracketed by analysing an FC‐1 standard zircon.

Systematic palaeontology Class CHONDRICHTHYES Huxley, 1880 Subclass ELASMOBRANCHII Order LAMNIFORMES Family LAMNIDAE Genus CARCHARODON Smith in Remarks. Glikman (1964, p. 104) placed the genera Carcharodon and Cosmopolitodus within the Carcharodontidae (Gill, 1893; mis‐cited as 1892 in Glikman) based on the following characters: teeth broad and blade‐like, crowns of upper lateral teeth dorsoventrally flattened, neck very small, roots short, base of the tail with keels. The idea of the Carcharodontidae was also raised separately by Whitley (1940) and supported by Applegate and Espinosa‐Arrubarrena (1996), who cited anatomical evidence including fin positions (but did not explicitly list the characters) and the presence of serrations and lateral denticles as synapomorphies. However, the characters of the Carcharodontidae listed by Glikman (1964) are not synapomorphies specific to Carcharodon. Furthermore, the separation of the Otodontidae from the Lamnidae and the presence of a weakly crenulated I. escheri do not restrict serrations and lateral cusplets to the Carcharodontidae, and therefore, the family is not supported. Glikman (1964) also differentiated the genus Cosmopolitodus from Carcharodon based on the absence of serrations and lateral cusplets. Carcharodon hubbelli sp. nov. Figure 6 Open in figure viewer PowerPoint Carcharodon hubbelli, UF 226255 (holotype). Scale bar represents 10 cm. Derivation of name. Named in honour of Dr. Gordon Hubbell of Gainesville, Florida, in recognition of the substantial contribution he has made to the field of shark palaeontology. Holotype. UF 226255 (Fig. 6), an articulated dentition including 222 teeth, 45 vertebral centra, portions of the left and right Meckel’s cartilages and palatoquadrates, and neurocranium. Type locality. Sud Sacaco (West) (15°33′S, 74°46′W), 5 km east of Lomas, Arequipa Region, Peru. Nearly 20–40 cm above the vertebrate‐bearing tuff bed, Pisco Formation; Upper Miocene. Referred specimens. Upper teeth (UF 245052–245057; Fig. 9). These teeth were recovered from the type locality (Sud Sacaco West), above the vertebrate‐bearing tuff bed. Diagnosis. A lamnid shark that differs from all other lamnids by the following unique combination of dental characteristics: (1) An A3 tooth distally inclined; (2) an A1 tooth that is the largest tooth in the dentition and is symmetrical; (3) an A2 tooth that is slightly larger than the a2 tooth; (4) serrations present but not fully developed. Description. The mandibular arch of UF 226255 is partially preserved, making it not possible to distinguish some features of the jaws. The left and right palatoquadrates are preserved anteriorly along with the symphysis. The symphysis of both palatoquadrates is square and deep. The upper dental bullae are also preserved in both palaquadrates. Within these bullae, the upper anterior teeth are found within a hollow, with an intermediate bar, or a labiolingual constriction of the cartilage, present between the third anterior tooth and the first lateral tooth. The distal portions of both palatoquadrates are not preserved, and the medial and lateral quadratomandibular joints are not discernable due to the dorsoventral flattening of the specimen. The Meckel’s cartilages are much deeper than the palatoquadrates. The posterior portions of both are highly fragmented, making the original shape impossible to discern. The lower symphysis is preserved; however, it is less deep than the symphysis of the palatoquadrates. The Meckel’s cartilages are situated much lower than the palatoquadrates, suggesting a subterminal mouth. Portions of the neurocranium are preserved; however, the structure is not discernable due to the dorsoventral flattening of the specimen. The occipital hemicentrum consists of the posterior half of a calcified double‐cone centrum, which articulates with the anteriormost centrum of the vertebral column. Other portions of sheet‐like cartilage are preserved within the gape of the jaws; however, it is not identifiable. Based on the position and preservation, they most likely represent the basal plate of the neurocranium. Other openings within these fragments of cartilage could represent foramina; however, due to the preservation, they probably represent areas of weathering. The dentition of C. hubbelli is represented by 222 teeth located on the palatoquadrates and Meckel’s cartilages. The teeth are flattened labiolingually, and triangular in shape (Fig. 7). The crowns have a slight convex curve lingually. There are five to six tooth series present for each tooth position. The teeth are weakly serrated, with anterior teeth averaging more than 30 serrations per side for anterior to no serrations for the distal‐most laterals. Of the teeth that do have serrations, there is an average of 8–12 serrations per centimetre on both edges of each tooth. Basal serrations on the teeth are larger than the other serrations on the edges. Figure 7 Open in figure viewer PowerPoint Functional tooth series of Carcharodon hubbelli, UF 226255 (holotype). Scale bar represents 5 cm. There are three anterior teeth present in each palatoquadrate. The A1 is symmetrical, and it is the largest in the tooth in the dentition. The A2 is also symmetrical and is slightly larger than the a2, while the A3 is distally inclined. The upper lateral teeth are also inclined distally (with L1 having the greatest inclination) and get progressively smaller towards the distal edge of the jaw. The roots of the teeth are relatively flat and rectangular in shape. In the Meckel’s cartilages, there are three anterior teeth present. Overall, the lower teeth have crowns that are more slender than those of the uppers. There is very little inclination seen in any of the lower teeth. As in the uppers, the teeth of the Meckel’s cartilages are progressively reduced distally. The roots of the lower teeth have a deep basal concavity and are thicker than those of the upper teeth, being somewhat lobate. There are 45 vertebral centra of UF 226255 preserved in the holotype. These centra are laterally compressed and are composed of two calcified cones connected by radiating calcified lamellae within the intermedalia (Fig. 8). These centra are asterospondylic. The articular surfaces are concave and show clear, calcified lamellae as well as pits in the centre that represent the notochordal constricture (Ridewood 1921; Gottfried and Fordyce 2001). In UF 226255, the occipital hemicentrum followed by the first 45 centra, which get larger in size in ascending order. Figure 8 Open in figure viewer PowerPoint Vertebral centrum of Carcharodon hubbelli, UF 226255 (holotype). Scale bar represents 10 mm. Remarks. Carcharodon hubbelli is an intermediate form between Carcharodon hastalis and Carcharodon carcharias and demonstrates a mosaic of characters from both species. Tooth crowns of C. hubbelli are convex and curve lingually similar to the crowns of C. hastalis. The serrations of C. hubbelli are enlarged basally but weaker overall than those of C. carcharias (but stronger than those seen in I. escheri) and appear to be intermediate between the unserrated C. hastalis and the coarsely serrated C. carcharias (Fig. 4). The A2 is symmetrical and is slightly larger than the a2, which are characters also seen in C. carcharias (Compagno 2001). Whereas the A3 is distally inclined, a character is found in C. hastalis. Therefore, the taxa may be useful as chronospecies, because they are diagnostically distinguishable by dental characteristics and are beneficial for biostratigraphy. Specimens collected in Upper Miocene deposits throughout the Pacific basin exhibit morphological gradation of dental characteristics from Carcharodon hastalis to C. hubbelli, and finally C. carcharias in the Early Pliocene. The observable transition of species through geologic time is denoted here by the designation of C. hastalis and C. hubbelli to the genus Carcharodon (Smith inMüller and Henle, 1838), which is given precedence over Cosmopolitodus (Glikman 1964). Furthermore, the diagnosis of Cosmopolitodus by Glikman is misleading since some Late Miocene C. hastalis teeth may have basal serrations.

Conclusions The recalibration of fossil horizons within the Pisco Formation finds ages are older than previously published (Muizon and Bellon 1980; Muizon and DeVries 1985; Muizon and Bellon 1986). While these changes are not exceptionally large, it does directly relate to the evolutionary history of the genus Carcharodon. The discovery and description of an outstanding specimen from the Pisco Formation further elucidate the taxonomy and palaeobiology of the white sharks. The hypothesis that I. escheri is a sister taxon of C. carcharias is refuted based on the Miocene and Pliocene distribution of Carcharodon fossils from the Pacific Basin and tooth morphology. The genus name Carcharodon is proposed for the species hastalis, hubbelli and carcharias based on dental characters shared between the taxa discussed above, and our interpretation of the C. hastalis‐hubbelli‐carcharias transition as an example of chronospecies. Palaeobiological information from UF 226255 reveals that this specimen grew at a rate comparatively slower than modern white sharks. MUSM 1470 confirms that the diet of C. hubbelli was at least partially comprised of marine mammals as early as the Late Miocene. Continued research of these specimens and newly discovered materials from the Pisco Formation and other fossil localities will only further advance our knowledge of the fossil lamnid sharks.

Acknowledgments Acknowledgements. This research is supported by National Science Foundation grants EAR 0418042 and 0735554. We especially thank Gordon Hubbell from Jaws International, Gainesville, Florida, for donating UF 226255 to the Florida Museum of Natural History as well as access to his collection and his wealth of knowledge of fossil sharks. We thank M. Stucchi from the Museo de Historia Natural of Lima, Peru, who provided assistance in the field in 2007. We also thank M. Siverson from the Western Australian Museum, Welshpool, Western Australia, and J. Bourdon of http://www.elasmo.com for discussions and constructive suggestions for the improvement of this manuscript. Thanks to E. Mavrodiev from the Florida Museum of Natural History for assistance with Russian translations. We also appreciate the comments from J. Bloch, R. Hulbert and J. Bourque from the Florida Museum of Natural History and two anonymous reviewers towards the improvement of this manuscript. This is University of Florida Contribution to Paleobiology 627. Any opinions, findings, conclusions or recommendations expressed in this paper are those of the author and do not necessarily reflect the views of the National Science Foundation. Editor. Adriana López‐Arbarello