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ORIGIN OF THE WHITE SHARK CARCHARODON (LAMNIFORMES: LAMNIDAE) BASED ON RECALIBRATION OF THE UPPER NEOGENE PISCO FORMATION OF PERU by DANA J. EHRET 1 * , BRUCE J. MACFADDEN 2 , DOUGLAS S. JONES 2 , THOMAS J. D E VRIES 3 , DAVID A. FOSTER 4 and RODOLFO SALAS-GISMONDI 5 1 Monmouth University, West Long Branch, NJ, 07764, USA; e-mail: [email protected] 2 Florida Museum of Natural History, University of Florida, Gainesville, FL 32611, USA; e-mails: [email protected]flmnh.ufl.edu, [email protected]flmnh.ufl.edu 3 Burke Museum of Natural History and Culture, University of Washington, Seattle, WA 98195, USA; e-mail: [email protected] 4 Department of Geological Sciences, University of Florida, Gainesville, FL 32611, USA; e-mail: [email protected]fl.edu 5 Departmento de Paleontologia de Vertebrados, Museo de Historia Natural Javier Prado, Universidad Nacional Mayor de San Marcos, Lima 11, Peru; e-mail: [email protected] *Corresponding author. Typescript received 21 October 2009; accepted in revised form 22 August 2012 Abstract: The taxonomic origin of the white shark, Car- charodon, is a highly debated subject. New fossil evidence presented in this study suggests that the genus is derived from the broad-toothed ‘mako’, Carcharodon (Cosmopolito- dus) 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. has- talis. Characters diagnostic to C. carcharias include the pres- ence tooth serrations and a symmetrical first upper anterior tooth that is the largest in the tooth row, while those indic- ative 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 anal- ysis. 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 evo- lution based on the calibration of the Neogene Pisco For- mation. Key words: Carcharocles, Cosmopolitodus, geochronology, Miocene, Isurus, strontium. Neoselachians are well represented in the fossil record worldwide during the Neogene and most of the fos- sil material found consists of isolated teeth. Shark teeth are shed by the thousands over an individual’s lifetime and have an enameloid crown that acts as a protective layer during fossilization. The cartilaginous skeleton of chondri- chthyans does not typically preserve except in rare instances where calcified vertebral centra, portions of the neurocrani- um and fin rays have been described (Uyeno et al. 1990; Shimada 1997; Siverson 1999; Gottfried and Fordyce 2001; Shimada 2007; Ehret et al. 2009a). The lack of more com- plete specimens of most fossil taxa has led to conflicting interpretations about the taxonomy and anatomy of many species. Such problems have caused much confusion in the nomenclature (including generic and specific names) and terminology (i.e. dental homologies) of fossil neosela- chians. One of the most debated enigmas within the neosela- chians focuses on the evolution and taxonomic placement of the white shark, Carcharodon carcharias (Linnaeus, 1758), within the Lamniformes. There are two distinct hypotheses regarding the evolution of C. carcharias that have been pro- posed in the literature. The first hypothesis places all large, serrated megatoothed sharks within the genus Carcharodon, including C. carcharias as well as those species referred to as Carcharocles, for example, Carcharocles megalodon (Jordan and Hannibal, 1923) and its related taxa. Based on this tax- onomy, the lineage of C. carcharias branched off as smaller forms of the megatoothed sharks and co-evolved alongside the truly large taxa, such as C. megalodon (Applegate and Espinosa-Arrubarrena 1996; Gottfried et al. 1996; Purdy 1996; Gottfried and Fordyce 2001; Purdy et al. 2001). The second hypothesis proposes that C. carcharias evolved from the broad-toothed Oxyrhina(Cosmopolitodus) [Palaeontology, Vol. 55, Part 6, 2012, pp. 1139–1153] ª The Palaeontological Association doi: 10.1111/j.1475-4983.2012.01201.x 1139

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  • ORIGIN OF THE WHITE SHARK CARCHARODON

    (LAMNIFORMES: LAMNIDAE) BASED ON

    RECALIBRATION OF THE UPPER NEOGENE PISCO

    FORMATION OF PERU

    by DANA J. EHRET1* , BRUCE J. MACFADDEN2 , DOUGLAS S. JONES2 ,

    THOMAS J. DEVRIES3 , DAVID A. FOSTER4 and RODOLFO SALAS-GISMONDI51Monmouth University, West Long Branch, NJ, 07764, USA; e-mail: [email protected] Museum of Natural History, University of Florida, Gainesville, FL 32611, USA; e-mails: [email protected], [email protected] Museum of Natural History and Culture, University of Washington, Seattle, WA 98195, USA; e-mail: [email protected] of Geological Sciences, University of Florida, Gainesville, FL 32611, USA; e-mail: [email protected] de Paleontologia de Vertebrados, Museo de Historia Natural Javier Prado, Universidad Nacional Mayor de San Marcos, Lima 11, Peru;

    e-mail: [email protected]

    *Corresponding author.

    Typescript received 21 October 2009; accepted in revised form 22 August 2012

    Abstract: The taxonomic origin of the white shark, Car-

    charodon, is a highly debated subject. New fossil evidence

    presented in this study suggests that the genus is derived

    from the broad-toothed mako, Carcharodon (Cosmopolito-

    dus) 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. has-

    talis. Characters diagnostic to C. carcharias include the pres-

    ence tooth serrations and a symmetrical first upper anterior

    tooth that is the largest in the tooth row, while those indic-

    ative 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 anal-

    ysis. The recalibration of the absolute dates suggests that

    Carcharodon hubbelli sp. nov. is Late Miocene (68 Ma) in

    age. This research revises and elucidates lamnid shark evo-

    lution based on the calibration of the Neogene Pisco For-

    mation.

    Key words: Carcharocles, Cosmopolitodus, geochronology,

    Miocene, Isurus, strontium.

    Neoselachians are well represented in the fossilrecord worldwide during the Neogene and most of the fos-

    sil material found consists of isolated teeth. Shark teeth are

    shed by the thousands over an individuals lifetime and

    have an enameloid crown that acts as a protective layer

    during fossilization. The cartilaginous skeleton of chondri-

    chthyans does not typically preserve except in rare instances

    where calcified vertebral centra, portions of the neurocrani-

    um and fin rays have been described (Uyeno et al. 1990;

    Shimada 1997; Siverson 1999; Gottfried and Fordyce 2001;

    Shimada 2007; Ehret et al. 2009a). The lack of more com-

    plete specimens of most fossil taxa has led to conflicting

    interpretations about the taxonomy and anatomy of many

    species. Such problems have caused much confusion in the

    nomenclature (including generic and specific names) and

    terminology (i.e. dental homologies) of fossil neosela-

    chians.

    One of the most debated enigmas within the neosela-

    chians focuses on the evolution and taxonomic placement of

    the white shark, Carcharodon carcharias (Linnaeus, 1758),

    within the Lamniformes. There are two distinct hypotheses

    regarding the evolution of C. carcharias that have been pro-

    posed in the literature. The first hypothesis places all large,

    serrated megatoothed sharks within the genus Carcharodon,

    including C. carcharias as well as those species referred to as

    Carcharocles, for example, Carcharocles megalodon (Jordan

    and Hannibal, 1923) and its related taxa. Based on this tax-

    onomy, the lineage of C. carcharias branched off as smaller

    forms of the megatoothed sharks and co-evolved alongside

    the truly large taxa, such as C. megalodon (Applegate and

    Espinosa-Arrubarrena 1996; Gottfried et al. 1996; Purdy

    1996; Gottfried and Fordyce 2001; Purdy et al. 2001).

    The second hypothesis proposes that C. carcharias evolved

    from the broad-toothed Oxyrhina (Cosmopolitodus)

    [Palaeontology, Vol. 55, Part 6, 2012, pp. 11391153]

    The Palaeontological Association doi: 10.1111/j.1475-4983.2012.01201.x 1139

  • hastalis (Agassiz, 18431844) while the megatoothed sharks

    belong to a separate family, the Otodontidae, within the

    Lamniformes (Casier 1960; Glikman 1964; Cappetta 1987;

    Ward and Bonavia 2001; Nyberg et al. 2006; Ehret et al.

    2009a). C. hastalis was originally assigned to the genus

    Oxyrhina and later to Isurus. However, based on affinities

    with C. carcharias, Glikman (1964) suggested the reassign-

    ment of all unserrated forms within the Carcharodon line-

    age to the genus Cosmopolitodus to reflect this relationship

    (Siverson 1999; Ward and Bonavia 2001). Under this

    hypothesis C. hastalis and C. carcharias represent chrono-

    species as C. hastalis is replaced by C. hubbelli and finally

    C. carcharias in geological time through a gradation. Fur-

    thermore, the teeth of C. hastalis do not share all characters

    with Isurus but instead are more similar to C. carcharias

    exhibiting triangular crowns that are labiolingually flat-

    tened, a flat labial face, a lingual face that is slightly convex

    and a root that is flat and quite high (Cappetta 1987). As

    such, the genus Carcharodon (Smith in Muller and Henle,

    1838) is the senior synonym of Cosmopolitodus (Glikman,

    1964) the proper genus name for C. hastalis. Fossil material

    collected from the Late Miocene and Early Pliocene of the

    Pacific Basin including Peru (specifically the Pisco Forma-

    tion), Chile, CA, USA, and Japan provide further evidence

    of this relationship (Muizon and DeVries 1985; Long 1993;

    Tanaka and Mori 1996; Stewart 1999, 2002; Yabe 2000;

    Suarez et al. 2006; Nyberg et al. 2006; Ehret et al. 2009a).

    The recent description of an articulated specimen of

    this intermediate form of Carcharodon recorded from the

    Pisco Formation presents important new insights into the

    evolutionary history and taxonomy of the genus (Ehret

    et al. 2009a). The described specimen was collected from

    Sud Sacaco (West), a locality referred to the Pliocene

    (c. 4.5 Ma) by Muizon and DeVries (1985). However, iso-

    topic calibration of fossil horizons exposed at Sud Sacaco

    (West), using strontium and zircon dating, allows us to

    reassess the age of the Carcharodon specimen. Based on

    the calibration of these horizons, it is our conclusion that

    the specimen should be referred to the Late Miocene

    rather than the Early Pliocene.

    The purpose of this paper is to present (1) a reassess-

    ment of the ages of some horizons within the Pisco For-

    mation, (2) formally describe a new species of the white

    shark and (3) relate changes in age and taxonomy to the

    evolution of the white shark within the Pacific Basin.

    METHODS AND MATERIALS

    Numerous studies indicate the Miocene Epoch was char-

    acterized by rapidly increasing 87Sr 86Sr in the globalocean; 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 of87Sr 86Sr in the shell calcium carbonate. When comparedwith the global seawater reference curve, these data allow

    us to estimate the age of the fossil molluscs for each

    locality (Table 1).

    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 ll of 3.5 N HNO3 and then loadedonto 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 spectrome-

    ter equipped with seven Faraday collectors and one Daly

    detector in the Department of Geological Sciences, Uni-

    versity 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 for88Sr, with corrections for instrumental discrimination

    made assuming 86Sr 88Sr = 0.1194. Errors in measured87Sr 86Sr are better than 0.00002 (2r), 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 thestrontium 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

    TABLE 1 . Strontium chemostratigraphic analyses of fossil mar-

    ine mollusc shells from the Pisco Formation.

    Fossil Horizon Mean87Sr 86Sr

    Age

    estimate (Ma)

    95% CI (Ma)

    El Jahuay 0.7089424 7.46 9.036.51

    Montemar 0.7089468 7.30 8.706.45

    Sud Sacaco

    (West)

    0.7089659 6.59 10.772.50

    Sud Sacaco

    (West)

    0.7089978 5.93 6.355.47

    Sacaco 0.7090005 5.89 6.764.86

    Ages and confidence intervals (CI) determined from McArthur

    et al. (2001).

    1140 P A L A E O N T O L O G Y , V O L U M E 5 5

  • (LA-MC-ICP-MS). We used a Nu Plasma mass spectrom-

    eter fitted with a U-Pb collector array at the Department

    of Geological Sciences, University of Florida. 238U and235U 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 3060 lmspots 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 Instru-

    ments. 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 correc-

    tion for isobaric interferences, particularly from 204Hg.

    Following blank acquisitions, individual zircons under-

    went ablation and analysis for c. 3060 s. The analyses of

    unknown zircons were bracketed by analysing an FC-1

    standard zircon.

    GEOLOGICAL SETTING

    The shallow-water, marine Pisco Formation of southwest-

    ern Peru consists of materials that accumulated during

    Late Miocene to Early Pliocene (c. 11.63.6 Ma); it is well

    known for its wealth of vertebrate fossils including elas-

    mobranchs, teleosts, chelonians, shore birds, seals, dol-

    phins, whales and aquatic sloths (Hoffstetter 1968;

    Muizon and DeVries 1985; Muizon and McDonald 1995;

    Muizon et al. 2002; Amiot et al. 2008; Ehret et al. 2009a).

    In addition to the presence of complete vertebrate skele-

    tons, the area also contains the partial remains of fossil

    sharks including associated tooth sets, vertebral centra

    and preserved cartilage of the jaws and neurocrania. The

    Pisco Formation also preserves the transition from Car-

    charodon hastalis to C. carcharias as demonstrated in the

    shark fossils recovered from localities within the forma-

    tion. Another taxon that exhibits intermediate characters

    between the two species, previously referred to as Car-

    charodon sp., is also abundant at some localities (particu-

    larly Sud Sacaco West and Sacaco) of the region (Muizon

    and DeVries 1985; Ehret et al. 2009a, b).

    The Pisco Formation crops out on the coastal plain of

    southern Peru from the town of Pisco south to Yauca

    (Fig. 1). The sediments include tuffaceous and diatoma-

    ceous sandstone and siltstone, ash horizons, bioclastic

    conglomerate (including the marine mollusc beds sampled

    in this study) and phosphorite, representing shallow mar-

    ine environments. These preserve cyclic marine transgres-

    sive and regressive events spanning the Middle Miocene

    (c. 13 Ma) through the Late Pliocene (c. 4 Ma; Muizon

    and DeVries 1985; DeVries 1998; Amiot et al. 2008).

    Around the region of Sacaco, Muizon and DeVries

    (1985) identified a composite section for the Pisco For-

    mation in the Sacaco area (which is not fully exposed in

    the region) consisting of five localities: El Jahuay (also

    known as Alto Grande), Aguada de Lomas, Montemar,

    Sud Sacaco (West) and Sacaco (Fig. 2). In addition to the

    exposed stratigraphy, these localities are also distinguished

    by a high diversity of fossilized vertebrate and inverte-

    brate species that found in numerous horizons (Marocco

    and Muizon 1988).

    El Jahuay is designated as the lowermost section of the

    Pisco Formation in the Sacaco area (Muizon and DeVries

    1985). The lowest tuff bed at El Jahuay is also the oldest

    in the Sacaco Basin and has been dated to 9.5 Ma (K-Ar

    dating, late Miocene; Muizon and DeVries 1985; Muizon

    and Bellon 1986). Below this bed, sediments are com-

    prised of a rounded boulder conglomerate (Muizon and

    DeVries 1985). In the 15 m exposed above this tuff, the

    section contains two shelly sandstone beds that are mixed

    with a bioturbated fossiliferous sandstone (Muizon and

    DeVries 1985). This layer had been designated as the El

    Jahuay vertebrate level (Fig. 2). Fossil selachians of inter-

    est to this study within the El Jahuay fossil level are iden-

    tified as C. hastalis and C. megalodon.

    14

    F IG . 1 . Map of Peru with localities within the Southern

    section of the Pisco Formation.

    E H R E T E T A L . : W H I T E S H A R K E V O L U T I O N 1141

  • At Aguada de Lomas, two tuffs were analysed using K-

    Ar isotopes and dated to 8 and 8.8 Ma, respectively

    (Fig. 2; Muizon and DeVries 1985; Muizon and Bellon

    1986). The sequence of these tuff layers and rounded

    boulder conglomerates at Aguada de Lomas led Muizon

    and Bellon (1986) to conclude that the lower section of

    this locality might have been produced by similar pro-

    cesses or even contemporaneous with the El Jahuay sec-

    tion (Muizon and DeVries 1985). Above these tuff beds,

    fine sandstone is the dominant lithology for the next

    80 m of the section (Muizon and Devries 1985). The fos-

    sil horizon presents at Aguada de Lomas caps these sand-

    stone layers and is comprised of cross-bedded sandstone,

    Skolithos burrows, and well-preserved vertebrate remains

    (Fig. 2; Muizon and DeVries 1985).

    The third exposed section of the Pisco Formation in

    the southern Pisco Basin can be found at Montemar

    (Fig. 2; Muizon and DeVries 1985). Sediments are com-

    prised of coarse and fine sandstone, siltstone and gypsum,

    along with mixed vertebrate and invertebrate fossils. The

    fossil horizon is considered to be uppermost Miocene

    (7.37.0 Ma) based on the co-occurrence of transitional

    Carcharodon teeth (Carcharodon hubbelli n. sp. of this

    study) and several molluscan species (Muizon and DeV-

    ries 1985). This fossil horizon is also noted for the pres-

    ence of articulated skeletons of baleen whales, penguins

    and sloths (Muizon and DeVries 1985).

    At Sud Sacaco (West), the Pisco Formation is repre-

    sented by a fossil horizon that is identified by the pres-

    ence of fossilized barnacle debris and shell beds that

    contain a diverse assemblage of molluscs (e.g. Dosinia

    (Scopoli, 1777)) and vertebrates (Fig. 2). These shell beds

    are capped by thick vertebrate-bearing tuffs, fining

    upward cycles of brachiopod-bearing sandstone, which

    contain serrated C. carcharias-like teeth (Muizon and

    DeVries 1985). Based on the stratigraphy and palaeontol-

    ogy, Muizon and Bellon (1980) concluded that the shell

    beds of the Sud Sacaco (West) fossil horizon were situ-

    ated stratigraphically below the vertebrate-bearing tuff

    bed dated at 3.9 Ma (i.e. Pliocene), and younger than the

    Miocene horizons present at El Jahuay and Montemar

    (Muizon and DeVries 1985).

    Finally, the youngest section within the southern

    Sacaco Basin is exposed at Sacaco. Sediments are mainly

    comprised of fine sandstone interbedded with a pebbly

    sandstone layer and two mollusc layers. The horizon also

    contains interbedded tuffs and cross-bedding is common.

    This horizon is considered to be above the vertebrate-

    bearing tough bed (3.9 Ma), which is exposed at Sud Sac-

    aco (West), and would indicate an Early Pliocene age

    (Fig. 2; Muizon and Bellon 1980; Muizon and DeVries

    1985). Additional sampling of invertebrate fossils and the

    tuff beds taken from El Jahuay (Alto Grande), Montemar,

    Sud Sacaco (West) and Sacaco during the summer of

    2007 were analysed for 87Sr 86Sr isotopes and zirconU-Pb and will be discussed below.

    OVERVIEW OF TAXONOMY ANDFOSSIL RECORD OF CARCHARODON

    As previously discussed, the evolutionary history of Car-

    charodon has been a contentious subject. To elucidate our

    current knowledge of the subject, it is important to

    review the hypotheses that have been previously pro-

    posed. We will then compare and incorporate the mate-

    rial from Peru into these paradigms. The taxonomy of

    F IG . 2 . Stratigraphic log of the Pisco Formation (based on

    Muizon and DeVries 1985). Abbreviations: AGL, Aguada de

    Lomas vertebrate horizon; ELJ, El Jahuay vertebrate horizon;

    MTM, Montemar vertebrate horizon; SAS, Sud Sacaco (West)

    vertebrate horizon; SAO, Sacaco vertebrate horizon.

    1142 P A L A E O N T O L O G Y , V O L U M E 5 5

  • the megatoothed sharks (including Otodus and Carcharo-

    cles) beyond their relationship to C. carcharias is not

    within the scope of this paper and will only be addressed

    to the extent necessary.

    The first hypothesis places the megatoothed sharks (Oto-

    dus and Carcharocles) and C. carcharias within the Lamni-

    dae. The serrated-toothed forms of the megatoothed sharks

    are assigned to the genus Carcharodon (referred to as Car-

    charocles here), while the unserrated form is recognized as

    being related and has been given a separate generic name,

    Otodus (Agassiz, 18331844; Applegate and Espinosa-Arru-

    barrena 1996; Gottfried et al. 1996; Purdy 1996; Purdy

    et al. 2001). It should be noted that a recent shift in para-

    digm recognizes Otodus as a chronospecies, thereby placing

    all species of Carcharocles into the genus Otodus, with the

    exception of megalodon, which has been referred to the

    genus Megaselachus (Glikman, 1964) (Casier 1960; Zhe-

    lezko and Kozlov 1999; Ward and Bonavia 2001). For the

    purpose of this discussion, however, we refer all serrated

    megatoothed sharks to Carcharocles based on the accepted

    taxonomy in the literature at the present time.

    The grouping of megatoothed sharks with Carcharodon

    carcharias was based on a number of dental characters

    including: (1) a symmetrical second anterior tooth; (2)

    large third anterior (intermediate) tooth that is inclined

    mesially; (3) upper anterior teeth that have a chevron-

    shaped neck on the lingual surface; (4) an ontogenetic

    gradation whereby the coarse serrations of a juvenile

    C. carcharias shift to fine serrations in the adult, the latter

    serrations resembling those of C. megalodon; (5) morpho-

    logical similarity between the teeth of young C. megalodon

    and adult C. carcharias (Gottfried et al. 1996; Gottfried

    and Fordyce 2001; Purdy et al. 2001; Ehret et al. 2009a).

    Following this hypothesis, C. carcharias is either the result

    of dwarfism from a larger megatoothed taxon or evolved

    via cladogenesis from a large megatoothed shark species

    sometime during the Palaeocene and coevolved alongside

    the other species (Gottfried et al. 1996; Martin 1996; Pur-

    dy 1996; Purdy et al. 2001).

    This taxonomy, however, does not truly reflect the fos-

    sil record. The characters listed above as diagnostic, unit-

    ing the megatoothed sharks and C. carcharias, are a result

    of individual variation, interpretation and homoplasy

    (Hubbell 1996; Shimada 2005). Variation and pathologic

    abnormalities within individual teeth can lead to the

    incorrect interpretation and identification of specimens.

    As an example, USNM 336204 has been described as lat-

    eral tooth of Carcharodon sp. (Purdy 1996) or C. carcha-

    rias (Gottfried and Fordyce 2001) from the Middle

    Miocene of the Calvert Formation of Maryland (Fig. 3).

    However, re-analysis of this specimen reveals that it is a

    small C. megalodon, based on the presence of a chevron-

    shaped neck, the thickness of the crown and the serration

    type. While the serrations are somewhat coarse for

    C. megalodon and could be misleading, the presence of

    the other characters listed above make this identification

    more plausible. Furthermore, the reconstruction of dental

    patterns of extinct sharks based on isolated teeth or disar-

    ticulated tooth sets is misleading when extant taxa are

    used as a template for interpretations (Shimada 2006,

    2007). Finally, the presence of serrations in both the

    megatoothed and white sharks is a result of homoplasy

    rather than a diagnostic character uniting the two taxa. A

    comparison of the serrations shows that they are in fact

    very different, with the Carcharocles exhibiting very fine

    and regular serrations while those of Carcharodon are

    coarse and irregular (Fig. 4).

    The second hypothesis keeps C. carcharias and the

    broad-toothed makos within the Lamnidae while the

    megatoothed sharks are reclassified into their own family,

    the Otodontidae within the Lamniformes. This hypothesis

    proposes that Carcharodon hastalis gave rise to the ser-

    rated-toothed Carcharodon carcharias during the Late

    Miocene or Early Pliocene (Casier 1960; Glikman 1964;

    Muizon and DeVries 1985; Cappetta 1987; Ward and Bo-

    navia 2001; Nyberg et al. 2006; Ehret et al. 2009a). This

    hypothesis would suggest that the lamnid and otodontid

    sharks last shared a common taxon in the Cretaceous

    (Casier 1960). Casier (1960) proposed that C. hastalis is

    ancestral to Carcharodon citing characters of dentition

    (although he did not list these characters) and offering

    as a possible transition between the taxa, Isurus escheri

    (Agassiz 18331843), which exhibits weak, fine crenula-

    tions (not true serrations) on the cutting edges of its teeth.

    It should be noted that Agassiz (18331844) separated

    the broad-toothed makos into numerous separate

    F IG . 3 . Carcharocles megalodon tooth, USNM 336204. Scale

    bar represents 10 mm.

    E H R E T E T A L . : W H I T E S H A R K E V O L U T I O N 1143

  • morphotypes, two of the most prominent were originally

    referred to Carcharodon (Oxyrhina) hastalis and Isurus

    (Oxyrhina) xiphodon (Agassiz, 18331844). His differenti-

    ation of the two taxa was based on C. hastalis having a

    noticeable flattening of the lingual crown foot and nar-

    rower tooth crowns compared to I. xiphodon but admit-

    ted that the latter was too weak of a character for

    identification (Agassiz 18331844; Purdy et al. 2001). Ler-

    iche (1926) included I. xiphodon in the synonymy of

    C. hastalis and noted the uncertainty of the origin of the

    types, which have since been lost (Ward and Bonavia

    2001). The species was recognized by Glikman (1964) and

    Purdy et al. (2001), who attributed specimens of C. has-

    talis from Peru, North Carolina and Belgium; the new

    species from Peru described herein; and I. escheri from

    Belgium to I. xiphodon based solely on the broadness of

    their crowns. Ward and Bonavia (2001) regarded I. xiph-

    odon as a nomen dubium based on the arguments of Leri-

    che (1926), the absence of any type specimens, and an

    unlikely provenance. Recent morphometric analysis of

    broad-toothed mako specimens by Whitenack and Gott-

    fried (2010) supports a morphological difference based on

    the broadness of the crown in broad-toothed makos.

    While this study might accurately separate these species,

    this could also represent sexual dimorphism or ontoge-

    netic changes in tooth morphology in one taxon. There

    may be a true delineation between broad- and narrow-

    crowned broad-toothed makos; however, based on the

    arguments of Leriche (1926) and Ward and Bonavia

    (2001), we agree that the name I. xiphodon is inappropri-

    ate and use C. hastalis for all forms of broad-toothed

    makos at the present time.

    The species I. escheri was originally placed in the genus

    Oxyrhina and later Isurus as a variant of C. hastalis (Agas-

    siz 18331844; Leriche 1926; Casier 1960). Specimens

    have been reported from the late Middle Miocene

    through the Early to Middle Pliocene (c. 144 Ma) of the

    northern Atlantic (including Germany, Belgium, the

    Netherlands and Denmark) with materials ranging from

    isolated teeth to an associated set of teeth and vertebrae

    from northern Germany (Agassiz 18331843; Leriche

    1926; Van den Bosch et al. 1975; Nolf 1988; Mewis and

    Klug 2006; Mewis 2008). The crenulations on the cutting

    edges of the teeth are much finer than the serrations of

    C. carcharias specimens found in the Pacific basin and

    tend to be along the entire cutting edge of the tooth (Ler-

    iche 1926; Van den Bosch et al. 1975; Nolf 1988). In

    addition to crenulations, some specimens may exhibit 13

    pairs of lateral cusplets, which are more pronounced in

    the lower teeth (Mewis 2008).

    The crown shape of I. escheri is less dorsoventrally flat-

    tened and thinner anterodorsally with a stronger distal

    inclination than either C. hastalis or Carcharodon (Fig. 5).

    This inclination is a result of a marked change in direction

    A B C

    D

    E

    F IG . 4 . Comparison of serration types. A, Carcharodon hastalis (UF 57267). B, Carcharodon hubbelli (UF 226255). C, Isurus escheri

    (UF 245058). D, Carcharocles megalodon (UF 217225). E, Carcharodon carcharias (G. Hubbell collection). Scale bar represents 10 mm.

    1144 P A L A E O N T O L O G Y , V O L U M E 5 5

  • of the distal cutting edge of the tooth crown and appears

    to be more pronounced in lateral teeth. The roots of the

    upper teeth also appear to be more lobate and angular

    than either C. hastalis or Carcharodon, which have very

    square, rectangular roots (Ehret et al. 2009a). The teeth of

    I. escheri appear to have stronger affinities with a more

    narrow-toothed form of C. hastalis, whereas the vertebral

    centra reported from Germany appear to have the typical

    amphicoelous lamniform morphology that is not diagnos-

    tic for refined taxonomic assessment above the ordinal

    level (Mewis and Klug 2006; Mewis 2008).

    While the latter hypothesis more accurately portrays

    the evolutionary history of Carcharodon, the designation

    of I. escheri as a sister taxon to C. carcharias based on cla-

    distic analysis of dental characters by Mewis (2008) could

    be misleading. Shimada (2005) has shown that cladistic

    analysis combining both dental and nondental characters

    of extant and fossil shark taxa generates considerable phy-

    logenetic noise. Comparisons of consensus trees using

    dental characters versus trees combining dental and all

    other morphological characters result in different topolo-

    gies. Tree statistics for the cladogram just using nondental

    characters were better than those combining dental and

    nondental characters (Shimada 2005). Shimada did

    acknowledge, however, that patterns indicated that dental

    characters are important for at least some phylogenetic

    signal. A review of the analysis by Mewis (2008) reveals

    that three of the synapomorphies uniting I. escheri and

    C. carcharias relate to the presence of serrations, which

    have evolved numerous times in the Lamniformes, while

    two others are dependent on correct tooth position

    assignment of disarticulated specimens. Additionally, the

    restricted fossil distribution of I. escheri to the Northern

    Atlantic and Mediterranean does not support the earliest

    Pliocene occurrences of C. carcharias in the Pacific, while

    appearances of the white shark are slightly later in the

    Atlantic.

    In contrast to I. escheri, the evolution of the white shark

    in the Pacific during the Late Miocene and Early Pliocene

    (c. 104 Ma) is well documented in the fossil records of

    Peru, Japan, California, Australia and Chile (Muizon and

    DeVries 1985; Kemp 1991; Long 1993; Tanaka and Mori

    1996; Stewart 1999, 2002; Yabe 2000; Nyberg et al. 2006;

    Ehret et al. 2009a). Based on the rich fossil record and the

    rejection of I. escheri as a sister taxon to C. carcharias, we

    agree more with the second origin hypothesis outlined

    above but propose a Pacific Basin origin for the genus

    Carcharodon with C. hastalis as a closely related taxon.

    Furthermore, we designate a new species of Carcharodon

    from the Pacific basin that represents an intermediate

    form between C. hastalis and C. carcharias.

    Institutional abbreviations. UF, Florida Museum of Natural His-

    tory (FLMNH) University of Florida; USNM, United States

    National Museum; MUSM, Museo de Historia Natural Javier

    Prado, Universidad Nacional Mayor de San Marcos, Lima, Peru.

    Terminology and anatomical abbreviations. Following Cappetta

    (1987) and Siverson (1999), specifically we define intermediate

    teeth as those that form on the intermediate bar, vary in number

    and are less than one half the crown heights of the anterior

    teeth.

    SYSTEMATIC PALAEONTOLOGY

    Class CHONDRICHTHYES Huxley, 1880

    Subclass ELASMOBRANCHII Bonaparte, 1838

    Order LAMNIFORMES Berg, 1958

    Family LAMNIDAE Muller and Henle, 1838

    Genus CARCHARODON Smith in Muller and Henle, 1838

    Remarks. Glikman (1964, p. 104) placed the genera Car-

    charodon and Cosmopolitodus within the Carcharodontidae

    (Gill, 1893; mis-cited as 1892 in Glikman) based on the

    A

    C D

    B

    F IG . 5 . Isurus escheri from the Delden Member (Early

    Pliocene), the Netherlands. AB, Upper Anterior tooth, UF

    245058. A, Labial view. B, Lingual view. CD, Upper Lateral

    tooth, UF 245059. C, Labial view. D, Lingual view. Scale bar

    represents 10 mm.

    E H R E T E T A L . : W H I T E S H A R K E V O L U T I O N 1145

  • 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 Car-

    charodontidae was also raised separately by Whitley (1940)

    and supported by Applegate and Espinosa-Arrubarrena

    (1996), who cited anatomical evidence including fin posi-

    tions (but did not explicitly list the characters) and the pres-

    ence of serrations and lateral denticles as synapomorphies.

    However, the characters of the Carcharodontidae listed by

    Glikman (1964) are not synapomorphies specific to Car-

    charodon. 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

    Derivation of name. Named in honour of Dr. Gordon Hubbell

    of Gainesville, Florida, in recognition of the substantial contribu-

    tion 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 Mec-

    kels cartilages and palatoquadrates, and neurocranium.

    Type locality. Sud Sacaco (West) (1533S, 7446W), 5 km eastof Lomas, Arequipa Region, Peru. Nearly 2040 cm above the

    vertebrate-bearing tuff bed, Pisco Formation; Upper Miocene.

    Referred specimens. Upper teeth (UF 245052245057; 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 devel-

    oped.

    Description. The mandibular arch of UF 226255 is partially pre-

    served, making it not possible to distinguish some features of

    the jaws. The left and right palatoquadrates are preserved anteri-

    orly along with the symphysis. The symphysis of both palatoqua-

    drates is square and deep. The upper dental bullae are also

    preserved in both palaquadrates. Within these bullae, the upper

    F IG . 6 . Carcharodon hubbelli, UF

    226255 (holotype). Scale bar represents

    10 cm.

    1146 P A L A E O N T O L O G Y , V O L U M E 5 5

  • 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 dis-

    cernable due to the dorsoventral flattening of the specimen.

    The Meckels cartilages are much deeper than the palatoqua-

    drates. The posterior portions of both are highly fragmented,

    making the original shape impossible to discern. The lower sym-

    physis is preserved; however, it is less deep than the symphysis

    of the palatoquadrates. The Meckels 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 poster-

    ior 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 preserva-

    tion, they probably represent areas of weathering.

    The dentition of C. hubbelli is represented by 222 teeth

    located on the palatoquadrates and Meckels 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 812

    serrations per centimetre on both edges of each tooth. Basal ser-

    rations on the teeth are larger than the other serrations on the

    edges.

    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 Meckels cartilages, there are three anterior teeth pres-

    ent. 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 Mec-

    kels 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 com-

    posed of two calcified cones connected by radiating calcified

    lamellae within the intermedalia (Fig. 8). These centra are as-

    terospondylic. The articular surfaces are concave and show clear,

    calcified lamellae as well as pits in the centre that represent the

    A

    B

    C

    D

    F IG . 7 . Functional tooth series of Carcharodon hubbelli, UF 226255 (holotype). Scale bar represents 5 cm.

    E H R E T E T A L . : W H I T E S H A R K E V O L U T I O N 1147

  • 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.

    Remarks. Carcharodon hubbelli is an intermediate form

    between Carcharodon hastalis and Carcharodon carcharias

    and demonstrates a mosaic of characters from both spe-

    cies. Tooth crowns of C. hubbelli are convex and curve

    lingually similar to the crowns of C. hastalis. The serra-

    tions 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. carcha-

    rias (Fig. 4). The A2 is symmetrical and is slightly larger

    than the a2, which are characters also seen in C. carcha-

    rias (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 transi-

    tion of species through geologic time is denoted here by

    the designation of C. hastalis and C. hubbelli to the genus

    Carcharodon (Smith in Muller 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.

    DISCUSSION

    Geology and stratigraphy. The new absolute ages obtained

    from molluscs recovered at many of the localities of the

    Pisco Formation suggest that deposition of the strata,

    now referred to the Pisco Fm, occurred earlier than

    thought previously. The results have direct bearing on the

    age of the holotype for C. hubbelli sp. nov. and evolution

    of white sharks in the Pacific basin.

    Previous dating of the tuff bed at Alto Grande within

    the El Jahuay vertebrate horizon resulted in an age of

    9.5 Ma based on K-Ar dating (Muizon and Bellon 1986;

    Muizon and DeVries 1985). Analysis of 55 zircon grains

    collected from the tuff bed at Alto Grande yielded 54 that

    gave ages that were Neoproterozoic through Cretaceous,

    which are obviously inherited or mixed detritus. One

    grain gave a concordant crystallization age of 10 1 Ma,

    which could also be inherited and should be treated as an

    upper limit for the horizon. The strontium ages of the

    shell layers overlying the tuff bed yielded an age range of

    9.036.51 Ma with a mean of 7.46 Ma (Fig. 2), which are

    younger than those for the ash layer. However, the upper

    limits of these ages are within the range for the other dat-

    ing methods making these age estimates congruent with

    previously published dates.

    Mollusc samples analysed from the Montemar horizon

    yield 87Sr 86Sr dates of 8.706.45 Ma with a mean of7.30 Ma. These ages are congruent with the estimation of

    Muizon and DeVries (1985) based on the vertebrate and

    invertebrate faunas (Fig. 2). While the resolution of the

    A B

    F IG . 8 . Vertebral centrum of Carcharodon hubbelli, UF 226255 (holotype). Scale bar represents 10 mm.

    1148 P A L A E O N T O L O G Y , V O L U M E 5 5

  • strontium data is not more precise than the estimate

    based on the molluscan fauna, it does confirm a Late

    Miocene age (Table 1). A Late Miocene (c. 8.76.5 Ma)

    age based on the correlation of gypsum beds with Aguada

    de Lomas, fossiliferous sandy siltstone with Sud Sacaco

    (West) and calibration of molluscan fauna was postulated

    by Muizon and DeVries (1985).

    Both geochemical methods, zircon U-Pb and strontium

    isotopic data, yield ages for the Sud Sacaco (West) level that

    are 12 million years older than reported previously by

    Muizon and DeVries (1985) and Tsuchi et al. (1988). Thus,

    making a change of age for the Sud Sacaco (West) horizon

    from the Early Pliocene to the Late Miocene (Gradstein

    et al. 2004). At Sud Sacaco (West), a thick Dosinia bed was

    sampled for strontium (Fig. 2). 87Sr 86Sr dates for the bedranged from 10.77 to 2.50 Ma with a mean of 6.59 Ma

    (Table 1). Additionally, the vertebrate-bearing tuff dis-

    cussed in Muizon and DeVries (1985) was located and sam-

    pled for zircon data. In total, 35 zircon grains were

    analysed with a majority being inherited or mixed detrital

    grains. Of the Oligocene and Miocene zircons identified,

    the youngest grain is 7 1 Ma and is probably the youn-

    gest age of the depositional range for the tuff. It should also

    be noted that the in situ holotype of Carcharodon hubbelli

    (UF 226255) was recovered 2040 cm above the base of the

    vertebrate-bearing layer (Ehret et al. 2009a).

    On the east side of Sud Sacaco (West) horizon,

    approximately 10 m above the vertebrate-bearing tuff

    layer, a shell bed containing abundant Ophiomorpha

    (Lundgren, 1891) burrows was sampled for strontium

    and yielded an age range of 6.355.47 Ma, with a mean

    of 5.93 Ma (Fig. 2). Previous methods of calibrating the

    Sud Sacaco (West) level include correlation of molluscs

    with white shark (Carcharodon) fossils. Furthermore, the

    reassignment of the shark fossils from C. carcharias

    (EarlyMiddle Pliocene) to C. hubbelli (Late Miocene

    Early Pliocene) also correlates with the older age for the

    horizon.

    For the Sacaco horizon, mollusc samples were collected

    near the Museo de Sacaco and yielded 87Sr 86Sr dates of6.764.86 Ma, with a mean of 5.89 Ma. This age is much

    older than the underlying tuff bed dated at 3.9 Ma by

    Muizon and Bellon (1980). Additional unpublished ArAr

    data from the Sacaco ash bed located on the floor of east-

    ern side of Quebrada Sacaco (locality DV 514-2 Snee)

    below the unconformity that separates Sacaco shell beds

    from upper portion of sequence on the hillsides of Sacaco

    yielded an age of 5.75 0.05 Ma (Lawrence Snee, USGS,

    sample collected 1987). These new Sr and Ar data are in

    disagreement with and much older than the 3.9 Ma age

    of Muizon and Bellon (1980). Therefore, the horizons

    exposed at the Sacaco locality appear to be older than

    previously recorded.

    Taxonomy and evolution of Carcharodon. The taxonomic

    evolution and placement of Carcharodon is a complex

    A

    G H I J K L

    B C D E F

    F IG . 9 . Individual upper teeth demonstrating the gradation of serrations from the Pisco Formation, Peru. Upper teeth from left to

    right, UF 245052245057. AF, labial view; GL, lingual view. Scale bar represents 10 mm.

    E H R E T E T A L . : W H I T E S H A R K E V O L U T I O N 1149

  • subject that has been compounded by the lack of more

    complete specimens and high levels of homoplasy in the

    tooth morphology of many species. While a C. hastalis-

    origin hypothesis has gained popularity in recent years,

    the timing and transition from one taxon to the other

    have remained unresolved. It is generally accepted that

    C. carcharias is directly related to Carcharodon hastalis

    and not the megatoothed sharks as previously discussed.

    Isurus escheri from the Middle Miocene through Early

    Pliocene of the Northern Atlantic has been suggested as a

    possible sister taxon to C. carcharias, based mainly on the

    presence of crenulations on the cutting edges of the teeth

    (Fig. 4). However, these fossils are restricted to the

    Northern Atlantic and Mediterranean and become extinct

    just prior to or as a result of the appearance of C. carcha-

    rias in the Atlantic by the mid-Pliocene. This species

    likely evolved from an Atlantic population of slim-

    toothed C. hastalis or hastalis-like taxon in the early Mio-

    cene. Meanwhile, materials from the Miocene Pacific

    Basin clearly demonstrate an intermediate form between

    C. hastalis and C. carcharias that is significantly different

    from I. escheri. The discovery and description of C. hub-

    belli from the Late Miocene of Peru and the recalibration

    of the Pisco Formation demonstrate the presence of ser-

    rated forms in the Miocene and early Pliocene of the

    Pacific, while there is general lack of specimens from the

    Atlantic at the same period.

    The distinction of C. hubbelli from I. escheri is vali-

    dated by the morphological differences exhibited in UF

    226255 and specimens of I. escheri examined from the

    Delden Member (Early Pliocene), the Netherlands (UF

    245058 and UF 245059) and the description of an associ-

    ated specimen from Germany (Mewis and Klug 2006;

    Mewis 2008). I. escheri has been identified from the Mid-

    dle Miocene (c. 14 Ma) to at least the Early Pliocene

    (c. 54 Ma) throughout Northern Europe. Van den Bosch

    (1978, 1980) differentiates I. escheri from the late Miocene

    as weakly crenulate and early Pliocene teeth as strongly

    crenulate types. However, this difference was not quanti-

    fied or figured in either of the studies and is inconsistent

    with our Early Pliocene samples that demonstrate weak

    crenulations (Fig. 5). C. hubbelli teeth show a progressive

    increase in the number and overall coarseness of serra-

    tions on their cutting edges from the Late Miocene to the

    Early Pliocene that are distinctively different and appear

    to evolve separately from I. escheri (Figs 4, 9). Addition-

    ally, the in situ dentition of UF 226255 demonstrates a

    mixture of characters expressed in both C. hastalis and

    C. carcharias, supporting our revised C. hastalis-origin

    hypothesis.

    Isurus escheri, on the other hand, appears to be a sepa-

    rate taxon more closely related to a narrow-crowned

    C. hastalis or hastalis-like taxon. Tooth serrations (or in

    this case crenulations) have evolved independently

    numerous times throughout the evolution of the sela-

    chians (Casier 1960; Cappetta 1987; Frazzetta 1988).

    Based on the living mako sharks, their tooth shape and

    overall body size, it is hypothesized that species within

    the genus Isurus were piscivorous (Applegate and Espin-

    osa-Arrubarrena 1996; Purdy et al. 2001; Aguilera and de

    Aguilera 2004). The evolution of serrations or crenula-

    tions would be advantageous for competition with other

    piscivorous shark taxa (C. hastalis, Galeocerdo (Muller

    and Henle, 1837)), Hemipristis (Agassiz, 18331843) and

    Carcharhinus (Blainville, 1816). Therefore, it is not sur-

    prising that more than one form would acquire serra-

    tions.

    The evolution of the white shark in the Pacific Basin is

    validated by the presence of weakly to moderately serrated

    teeth in the fossil deposits from the Late Miocene and

    Early Pliocene of North and South America, Asia and

    Australia (Muizon and DeVries 1985; Kemp 1991; Long

    1993; Tanaka and Mori 1996; Yabe 2000; Stewart 1999,

    2002; Nyberg et al. 2006; Ehret et al. 2009a). While many

    of these specimens from the Pacific represent different

    degrees of evolution between C. hastalis and C. carcharias,

    it is not possible to separate these based on isolated teeth.

    A complete tooth set, exhibiting more definitive charac-

    ters, would be required to differentiate potentially differ-

    ent forms. Therefore, these teeth are assigned to the

    species Carcharodon hubbelli; previous identifications as

    I. escheri (Kemp 1993), Carcharodon sp. (Nyberg et al.

    2006; Ehret et al. 2009a) or C. carcharias (Muizon and

    DeVries 1985; Long 1993; Tanaka and Mori 1996) should

    be amended to reflect this new assignment.

    Additional research on C. hubbelli has shed light on the

    palaeobiology of this species (Ehret et al. 2009a, b). Incre-

    mental growth analyses of the vertebral centra of UF

    226255 have revealed annular growth patterns that relate

    to the life history of this specimen. Growth rings visible

    using X-radiography appear to represent annual periodic-

    ity based on the calibration of oxygen and carbon isotope

    analysis within the rings. Counts of the growth rings

    using the X-radiographs provide an age estimate of at

    least 20 years. The overall length of the specimen was

    estimated using the averages of both crown height and

    vertebral centrum diameter regressions from previously

    published studies of C. carcharias. Resulting data provide

    total length estimates between 4.89 and 5.09 m. for the

    specimen. Based on growth curves of modern C. carcha-

    rias, UF 226255 appears to have been growing at a slower

    rate than white sharks today.

    Further palaeobiological information about C. hubbelli

    includes a partial mysticete whale mandible from the SAS

    layer containing a partial tooth crown MUSM 1470,

    housed in the collection of the Museo de Historia Natural

    Javier Prado, Universidad Nacional Mayor de San Mar-

    cos, Lima, Peru (MUSM), described by Ehret et al.

    1150 P A L A E O N T O L O G Y , V O L U M E 5 5

  • (2009b). This specimen represents direct evidence of feed-

    ing behaviour of the species in the Late Miocene. The

    presence of tooth serrations and MUSM 1470 provides

    definitive proof that C. hubbelli was adapted for taking

    marine mammals as prey as early as c. 6.5 Ma.

    CONCLUSIONS

    The recalibration of fossil horizons within the Pisco For-

    mation 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 evolution-

    ary history of the genus Carcharodon. The discovery and

    description of an outstanding specimen from the Pisco

    Formation further elucidate the taxonomy and palaeobi-

    ology 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 par-

    tially 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 knowl-

    edge of the fossil lamnid sharks.

    Acknowledgements. This research is supported by National Sci-

    ence Foundation grants EAR 0418042 and 0735554. We espe-

    cially 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. Stuc-

    chi from the Museo de Historia Natural of Lima, Peru, who

    provided assistance in the field in 2007. We also thank M. Siver-

    son from the Western Australian Museum, Welshpool, Western

    Australia, and J. Bourdon of http://www.elasmo.com for discus-

    sions 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 manu-

    script. 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 nec-

    essarily reflect the views of the National Science Foundation.

    Editor. Adriana Lopez-Arbarello

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