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ORIGIN of the WHITE SHARK CARCHARODON (LAMNIFORMES: LAMNIDAE) BASED on RECALIBRATION OE the UPPER NEOGENE PISGO FORMATION of PERU by DANA J

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ORIGIN of the WHITE SHARK CARCHARODON (LAMNIFORMES: LAMNIDAE) BASED on RECALIBRATION OE the UPPER NEOGENE PISGO FORMATION of PERU by DANA J [Palaeontology, Vol. 55, Part 6, 2012, pp. 1139-1153] ORIGIN OF THE WHITE SHARK CARCHARODON (LAMNIFORMES: LAMNIDAE) BASED ON RECALIBRATION OE THE UPPER NEOGENE PISGO FORMATION OF PERU by DANA J. EHRET'^ BRUCE J. MACEADDEN^ DOUGLAS S. JONES^ THOMAS J. DEVRIES^ DAVID A. EOSTER^ andRODOlYO SALAS-GISMONDI^ 'Monmouth University, West Long Branch, NJ, 07764, USA; e-mail: [email protected] ^Florida Museum of Natural History, University of Florida, Gainesville, FL 32611, USA; e-mails: [email protected], [email protected] 'Burke Museum of Natural History and Culture, University of Washington, Seattle, WA 98195, USA; e-mail: [email protected] ^Department of Geological Sciences, University of Florida, Gainesville, FL 32611, USA; e-mail: [email protected] 'Departmento de Paleontología 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- ative of C. hastalis include a mesially slanted third anterior charodon, is a highly debated subject. New fossil evidence (intermediate) tooth. We also provide a recalibration of presented in this study suggests that the genus is derived critical fossil horizons within the Pisco Formation, Peru from the broad-toothed 'mako', Carcharodon (Cosmopolito- using zircon U-Pb dating and strontium-ratio isotopic anal- dus) hastalis, and includes the new species C. hubbelli sp. ysis. The recalibration of the absolute dates suggests that nov. - a taxon that demonstrates a transition between Carcharodon hubbelli sp. nov. is Late Miocene (6-8 Ma) in C. hastalis and Carcharodon carcharías. Specimens from the age. This research revises and elucidates lamnid shark evo- Pisco Formation clearly demonstrate an evolutionary mosaic lution based on the calibration of the Neogene Pisco For- of characters of both recent C. carcharias and fossil C. has- mation. talis. Characters diagnostic to C. carcharias include the pres- ence tooth serrations and a symmetrical first upper anterior Key words: Carcharocles, Cosmopolitodus, geochronology, tooth that is the largest in the tooth row, while those indic- Miocene, Ismus, strontium. NEOSELACHIANS are well represented in the fossil One of the most debated enigmas within the neosela- record worldwide during the Neogene and most of the fos- chians focuses on the evolution and taxonomic placement of sil material found consists of isolated teeth. Shark teeth are the white shark, Carcharodon carcharias (Linnaeus, 1758), shed by the thousands over an individual's lifetime and within the Lamrdformes. There are two distinct hypotheses have an enameloid crown that acts as a protective layer regarding the evolution of C. carcharias that have been pro- during fossilization. The cartilaginous skeleton of chondri- posed in the literature. The first hypothesis places all large, chthyans does not typically preserve except in rare instances serrated megatoothed sharks within the genus Carcharodon, where calcified vertebral centra, portions of the neurocrani- including C. carcharias as well as those species referred to as um and fin rays have been described (Uyeno et al. 1990; Carcharocles, for example, Carcharocles megalodon (Jordan Shimada 1997; Siverson 1999; Gottfried and Fordyce 2001; and Hannibal, 1923) and its related taxa. Based on this tax- Shimada 2007; Ehret et al. 2009fl). The lack of more com- onomy, the lineage of C. carcharias branched off as smaller plete specimens of most fossil taxa has led to conflicting forms of the megatoothed sharks and co-evolved alongside interpretations about the taxonomy and anatomy of many the truly large taxa, such as C. megalodon (Applegate and species. Such problems have caused much confusion in the Esprnosa-Arrubarrena 1996; Gottfried et al 1996; Purdy nomenclature (including generic and specific names) and 1996; Gottfried and Fordyce 2001; Purdy et al. 2001). terminology (i.e. dental homologies) of fossil neosela- The second hypothesis proposes that C. carcharias evolved chians. from the broad-toothed 'Oxyrhina' {Cosmopolitodus) © The Palaeontological Association doi: 10.1111/J.1475-4983.2012.01201.X 1139 1140 PALAEONTOLOGY, VOLUME 55 hastalis (Agassiz, 1843-1844) while the megatoothed sharks Hodell and Woodruff 1994, Oslick et al. 1994, Miller and belong to a separate family, the Otodontidae, within the Sugarman 1995, Martin et al. 1999, McArthur et aï. Lamniformes (Casier 1960; Glikman 1964; Cappetta 1987; 2001). We analysed three fossil marine mollusc shells Ward and Bonavia 2001; Nyberg et al. 2006; Ehret et al. from each of five localities to determine the ratio of 2009fl). C. hastalis was originally assigned to the genus *'Sr/*''Sr in the shell calcium carbonate. When compared Oxyrhina and later to Isurus. However, based on affinities with the global seawater reference curve, these data allow with C. cardiarias, Glikman (1964) suggested the reassign- us to estimate the age of the fossil molluscs for each ment of all unserrated forms within the Carcharodon line- locality (Table 1). age to the genus Cosmopolitodus to reflect this relationship For isotopic analyses, we first ground off a portion of (Siverson 1999; Ward and Bonavia 2001). Under this the surface layer of each shell specimen to reduce possible hypothesis C. hastalis and C carcharías represent chrono- contamination. Areas showing chalkiness or other signs of species as C. hastalis is replaced by C. hubhelli and finally diagenetic alteration were avoided. Approximately 0.01- C. carcharias in geological time through a gradation. Fur- 0.03 g of aragonite or low-magnesium calcite powder was thermore, the teeth of C. hastalis do not share all characters recovered from each fossil sample. The powdered samples with Isurus but instead are more similar to C. carcharias were dissolved in 100 /d of 3.5 N HNO3 and then loaded exhibiting triangular crowns that are labiolingually flat- onto cation exchange columns packed with strontium- tened, a flat labial face, a lingual face that is slightly convex selective crown ether resin (Eichrom Technologies, Inc., and a root that is flat and quite high (Cappetta 1987). As Lisle, IL, USA) to separate Sr from other ions (Pin and such, the genus Carcharodon (Smith in Müller and Henle, Bassin 1992). Sr isotope analyses were performed on a 1838) is the senior synonym of Cosmopolitodus (Glikman, Micromass Sector 54 thermal ionization mass spectrome- 1964) the proper genus name for C. hastalis. Fossil material ter equipped with seven Faraday collectors and one Daly collected from the Late Miocene and Early Pliocene of the detector in the Department of Geological Sciences, Uni- Pacific Basin including Peru (specifically the Pisco Forma- versity of Florida. Sr was loaded onto oxidized tungsten tion), Chile, CA, USA, and lapan provide further evidence single filaments and run in triple collector dynamic mode. of this relationship (Muizon and DeVries 1985; Long 1993; Data were acquired at a beam intensity of about 1.5 V for Tanaka and Mori 1996; Stewart 1999, 2002; Yabe 2000; *^Sr, vnth corrections for instrumental discrimination Suarez et al. 2006; Nyberg et al. 2006; Ehret et al. 2009a). made assuming ^''Sr/^^Sr = 0.1194. Errors in measured The recent description of an articulated specimen of "^Sr/^Sr are better than ±0.00002 {2a), based on long- this intermediate form of Carcharodon recorded from the term reproducibility of NIST 987 (^^Sr/'^Sr = 0.71024). Pisco Formation presents important new insights into the Age estimates were determined using the Miocene portion evolutionary history and taxonomy of the genus (Ehret of Look-Up Table Version 4:08/03 associated with the et al. 2009fl). The described specimen was collected from strontium isotopic age model of McArthur et al. (2001). Sud Sacaco (West), a locality referred to the Pliocene Zircons were extracted from samples using standard (c. 4.5 Ma) by Muizon and DeVries (1985). However, iso- crushing, density separation and magnetic separation topic calibration of fossil horizons exposed at Sud Sacaco techniques. The zircons were hand picked, mounted in (West), using strontium and zircon dating, allows us to epoxy plugs along with the reference zircon FC-1 (Paces reassess the age of the Carcharodon specimen. Based on and Miller 1993) and analysed using laser ablation multi- the calibration of these horizons, it is our conclusion that collector inductively coupled plasma mass spectrometry 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- TABLE 1. Strontium chemostratigraphic analyses of fossil mar- ment of the ages of some horizons within the Pisco For- ine mollusc shells from the Pisco Formation. mation, (2) formally describe a new species of the white Fossil Horizon Mean 95% CI (Ma) shark and (3) relate changes in age and taxonomy to the Age ''^Sr/^'^Sr estimate (Ma) evolution of the white shark within the Pacific Basin. El Jahuay 0.7089424 7.46 9.03-6.51 Montemar 0.7089468 7.30 8.70-6.45 METHODS AND MATERIALS Sud Sacaco 0.7089659 6.59 10.77-2.50 (West) Numerous studies indicate the Miocene Epoch was char- Sud Sacaco 0.7089978 5.93 6.35-5.47 acterized by rapidly increasing *''Sr/''*Sr in the global (West) Sacaco 0.7090005 5.89 6.76-4.86 ocean; therefore, it is especially amenable to dating and correlating marine sediments using strontium isotope Ages and confidence intervals (CI) determined from McArthur chemostratigraphy (Hodell et al 1991; Miller et al. 1991, et al (2001). EHRET ET AL.: WHITE SHARK EVOLUTION 1141 (LA-MC-ICP-MS). We used a Nu Plasma mass spectrom- eter fitted with a U-Pb collector array at the Department À of Geological Sciences, University of Florida. ^^*U and N ^^^U abundances were measured on Faraday collectors and ^°^Pb, ^°*Pb and ^°*Pb abundances on ion counters. The Nu Plasma mass spectrometer is coupled with a New Wave 213 nm ultraviolet laser for ablating 30-60 fim spots within zircon grains.
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