Historical Biology An International Journal of Paleobiology ISSN: 0891-2963 (Print) 1029-2381 (Online) Journal homepage: http://www.tandfonline.com/loi/ghbi20 A new elusive otodontid shark (Lamniformes: Otodontidae) from the lower Miocene, and comments on the taxonomy of otodontid genera, including the ‘megatoothed’ clade Kenshu Shimada, Richard E. Chandler, Otto Lok Tao Lam, Takeshi Tanaka & David J. Ward To cite this article: Kenshu Shimada, Richard E. Chandler, Otto Lok Tao Lam, Takeshi Tanaka & David J. Ward (2016): A new elusive otodontid shark (Lamniformes: Otodontidae) from the lower Miocene, and comments on the taxonomy of otodontid genera, including the ‘megatoothed’ clade, Historical Biology, DOI: 10.1080/08912963.2016.1236795 To link to this article: http://dx.doi.org/10.1080/08912963.2016.1236795 Published online: 03 Oct 2016. Submit your article to this journal View related articles View Crossmark data Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ghbi20 Download by: [174.18.14.164] Date: 03 October 2016, At: 11:32 HISTORICAL BIOLOGY, 2016 http://dx.doi.org/10.1080/08912963.2016.1236795 A new elusive otodontid shark (Lamniformes: Otodontidae) from the lower Miocene, and comments on the taxonomy of otodontid genera, including the ‘megatoothed’ clade Kenshu Shimadaa,b,c, Richard E. Chandlerd, Otto Lok Tao Lame, Takeshi Tanakaf and David J. Wardg aDepartment of Environmental Science and Studies, DePaul University, Chicago, IL, USA; bDepartment of Biological Sciences, DePaul University, Chicago, IL, USA; cSternberg Museum of Natural History, Fort Hays State University, Hays, KS, USA; dDepartment of Mathematics, North Carolina State University, Raleigh, NC, USA; eOral Rehabilitation, Faculty of Dentistry, The University of Hong Kong, Hong Kong SAR, China; fThe Japanese Club for Fossil Shark Tooth Research, 1-25-40-311, Sakawa, Odawara, Japan; gDepartment of Earth Sciences, The Natural History Museum, London, UK ABSTRACT ARTICLE HISTORY We describe a new large otodontid lamniform shark, Megalolamna paradoxodon gen. nov. et sp. nov., Received 2 July 2016 chronostratigraphically restricted to the early Miocene (Aquitanian–Burdigalian). This new species is based Accepted 11 September 2016 on isolated teeth found from five globally distributed localities: the Jewett Sand in southern California, USA; the Pungo River Formation of North Carolina, USA; the Chilcatay Formation of Peru; the Oi Formation KEYWORDS in Mie Prefecture, Japan; and the O’oshimojo Formation in Nagano Prefecture, Japan. Extrapolations based Elasmobranchii; evolution; fossil; taxonomy; phylogeny on available published data on modern macrophagous lamniforms suggest that the largest specimen of M. paradoxodon gen. nov. et sp. nov. possibly came from an individual that measured at least 3.7 m in total length. All specimens came from deposits in the mid-latitudinal zones representing shallow-water, shelf- type, coastal environments. Its dentition likely exhibited monognathic heterodonty suited for capturing and cutting relatively large prey (e.g. medium-sized fishes). We recommend the genus Otodus to include sharks of the ‘megatoothed’ (e.g. megalodon) lineage in order to avoid Otodus paraphyly. We also propose the following phylogenetic hypothesis: [Kenolamna + [Cretalamna + [Megalolamna + Otodus]]]. ZooBank LSID for the genus Megalolamna is: urn:lsid:zoobank.org:act:B4791DEF-4D96-4FEB-9B7B- 0EF816B96079 ZooBank LSID for the species Megalolamna paradoxodon is: urn:lsid:zoobank.org:act:7D3D7442-53C6- 43A2-9E8D-6339729565B6 Introduction Fossil shark teeth are arguably the most commonly collected vertebrate fossils (Hubbell 1996). Whereas reports of new elasmo- The shark order Lamniformes is a major elasmobranch clade that branch taxa are common, such discoveries are typically smaller includes the vast majority of gigantic predaceous forms. Iconic forms represented by smaller teeth—the size range typically extant taxa in the group include the goblin (Mitsukurina Jordan), difficult to find in the field but generally explored through bulk sandtiger (Carcharias Rafinesque and Odontaspis Agassiz), por- sampling of sediments specifically targeting smaller remains (e.g. beagle (Lamna Cuvier), mako (Isurus Rafinesque), and white Shimada & Ward, in press). Excluding examples of erecting new (Carcharodon Smith) sharks, and numerous extinct forms taxa by redescribing existing taxa, descriptions of larger (e.g. teeth that belong to this order are also known in the fossil record. exceeding 3 cm in height) taxa entirely new to science are rare, A major adaptive radiation of lamniforms took place during and one would expect that the situation is particularly true for the Late Cretaceous (Maisey et al. 2004), including the rise of well-exploited and well-sampled Neogene localities that yield large cosmopolitan taxa such as Cretalamna Glikman, Cretoxyrhina taxa, such as Carcharodon hastalis (Agassiz), Parotodus benedinii Glikman, and Cardabiodon Siverson (Cappetta 2012). Numerous (Le Hon), and ‘megatoothed sharks’ (e.g. California and North fossil lamniforms also evolved during the Cenozoic, including Carolina). In this paper, we report a new enigmatic otodontid gigantic taxa such as Otodus Agassiz, Parotodus Cappetta, and lamniform from the lower Miocene that is inferred to be a large the so-called ‘megatoothed (megalodon) shark’ that is thought species estimated to have reached at least 3.7 m in total length. The to have reached to at least 15 m in length (Gottfried et al. 1996; purpose of this paper is twofold: (1) to describe the new taxon that Shimada 2003; Pimiento & Balk 2015). CONTACT Kenshu Shimada [email protected] © 2016 Informa UK Limited, trading as Taylor & Francis Group 2 K. SHimada et AL. Figure 1. Early Miocene (Aquitanian–Burdigalian) paleogeographic map (center; after Smith et al. 1994, p. 27) along with present-day maps showing four ‘early’ Miocene shark fossil localities (X marks) described in this paper (scale bar = 100 km). (a) Pyramid Hill Sand Member of Jewett Sand, Kern County, California, USA; (b) Pungo River Formation, Beaufort County, North Carolina, USA; (c) Chilcatay Formation, Ica, Peru; (d) Oi Formation of Ichishi Group, Tsu City, Mie Prefecture, Japan. constitutes a new genus and a new species, and (2) to comment quite widespread geographically, coming from five different on some issues concerning the systematics of otodontid sharks. localities in four separate geographic regions: western and east- ern USA, Japan, and Peru (Figure 1). Geographical and stratigraphic context The western USA example is represented by one tooth that comes from the Pyramid Hill Sand Member of the Jewett Sand The newly described taxon is based on five isolated tooth spec- (Mitchell & Tedford 1973) in Kern County, California, USA. imens. They are chronostratigraphically restricted to the early The Pyramid Hill Sand largely consists of silty sand interbedded Miocene and possibly earliest middle Miocene. However, it is with concretionary sandy silts and sandstone beds (Mitchell & Historical BioloGY 3 Tedford 1973), although the exact horizon for the tooth speci- Subcohort Neoselachii Compagno 1977 men within the stratigraphic member is uncertain. Pectinid and Order Lamniformes Berg 1958 foraminiferan fossils suggest an age of 23 ± 1 Ma or Saucesian Family Otodontidae Glikman 1964 for the stratigraphic member (Olson 1988, p. 192). The early Megalolamna new genus Saucesian Stage is correlated with planktonic foraminiferal zone N4 (Berggren 1972, p. 202, figure 4). These biostratigraphical Type species zones correspond to the earliest Aquitanian (Shimada et al. 2014, Megalolamna paradoxodon sp. nov. described below; Pyramid figure 2; see also Welton 2015, figure 2). Hill Sand Member (early Miocene) of Jewett Sand, Kern County, Two teeth described in this paper come from the Pungo River California, USA. Formation at Lee Creek Mine, Beaufort County, North Carolina, USA. The Pungo River Formation consists of phosphatic sands, silts, and clays, interbedded with diatomaceous clays (Miller Diagnosis 1982). Their exact stratigraphic positions are uncertain, but they Lamniform differing from all known species of otodontids (sensu were most likely collected from the upper half of the formation this paper; see Discussion) by the following combination of charac- (Beds 4–7 of Gibson 1967, p. 639, figure 4), the richer underlying ters: tooth consisting of a sharply-pointed, relatively tall, triangular phosphate having been extracted. Based on previous micropal- main cusp, one prominent pair of triangular lateral cusplets, and eontological correlations, Ward (2008) dates the Pungo River strongly bilobed root; main cusp erect, slightly inclined distally, Formation as mid-Burdigalian, or late early Miocene. This is or gently curved distally; lingual crown face very convex without compatible with the strontium isotope date for the top of the ornamentation; labial crown face flat or subtly convex except center Pungo River Formation of 16 Ma ± 0.5 Ma given by Denison et al. of base with weak depression; height and width of each lateral (1993) which equates with the Burdigalian–Langhian boundary. cusplet nearly equal with tendency to point outward; both mesial One specimen comes from the early Miocene Chilcatay and distal cutting edges of main cusp and lateral cusplets smooth Formation in Ica, Peru, although its exact locality in the Ica area and razor-like, and continuous from apex to base; main cusp and