Lamniformes: Otodontidae) from the Lower Miocene, and Comments on The

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A new elusive otodontid shark (Lamniformes: Otodontidae) from the lower Miocene, and comments on the...

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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).

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 eastern 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 as well as its exact stratigraphic horizon within the formation lateral cusplets nearly erect to gently curved lingually; concave are uncertain. The Chilcatay Formation is estimated to be 250 m crown base and distinct tooth neck on lingual face; prominent thick and consists of siltstones and sandstones interbedded with tooth neck also on labial face in tall teeth, forming rounded ledge diatomaceous units through three transgressive cycles (Macharé with thin enameloid layer that grades into enameloid of main cusp & Fourtanier 1987; Dunbar et al. 1990). Chronostratigraphically, and lateral cusplets; bilobed root with rounded basal tips and mod- the formation ranges from about 24 Ma (earliest early Miocene) erately tight basal concavity in between; root overall robust but to 15 Ma (early middle Miocene) where its upper part is assigned particularly at lingual protuberance that generally exhibits one or to N8 foraminiferan zone (DeVries 1988, 1998; Dunbar et al. two prominent and a few smaller nutritive foramina; root width 1990). This range corresponds to Aquitanian–Burdigalian in age. slightly wider than total crown width; osteodentine tooth histology. The Japanese example is represented by a tooth found from the Mitsugeno Shaly Sandstone Member of the Oi Formation of the Ichishi Group in Tsu City, Mie Prefecture. As the name Etymology suggests, the Mitsugeno member is dominated by shaly sand- The genus name,Megalolamna , named for its large teeth super- stone where fossil invertebrates and elasmobranchs are com- ficially resembling the genus Lamna: Megalo (Greek megas) = mon (Shibata 1967; Tanaka 2013). According to Ito (1982), the great; and lamna = lamniform genus Lamna. member is equivalent to planktonic foraminiferan zones N7–N8. On the basis of other invertebrate fossils, Itoigawa and Shibata (1992) suggested the stratigraphic unit to be 17.5–17 Ma, and Megalolamna paradoxodon new species Sugisawa and Honda (1999) 16–18 Ma. Thus, the Mitsugeno Shaly Sandstone Member is interpreted to be late early Miocene Synonymy (Tanaka 2013), or late Burdigalian, in age. Otodus sp.: Hasegawa & Uyeno 1967, p. 116, plate 21, figure 1a–c. Lamna sp.: Renz 2009, p. 158. Systematic paleontology Lamnidae gen. et sp. indet.: Tanaka 2013, p. 99, plate 12, figure Specimens (Figure 2) described in this paper are housed in 11a–c. the following four institutions: Kanagawa Prefectural Museum Brachycarcharias sp.?: Chandler (ed.) 2015, p. 49. (KMP), Odawara City, Japan; San Marcos Museum of Natural History (MUSM), Vertebrate Paleontology Department, Lima, Diagnosis Peru; North Carolina Museum of Natural Sciences (NCSM), As for Megalolamna gen. nov. (see above). Vertebrate Paleontology collection, Raleigh, North Carolina, USA; and University of California at Berkeley, Museum of Paleontology (UCMP), Berkeley, California, USA. Etymology Class Chondrichthyes Huxley 1880 The species name, paradoxodon, named for its paradoxical occur- Subclass Elasmobranchii Bonaparte 1838 rence of teeth: paradox (Latin paradoxum) = paradox; and odon Cohort Euselachii Hay 1902 (variant of Greek odous) = tooth. 4 K. Shimada et al.

Figure 2. Teeth of Megalolamna paradoxodon gen. nov. et sp. nov. (a)–(f) UCMP 112146 (holotype) from Pyramid Hill Sand Member of Jewett Sand, Kern County, California, USA; (g)–(j) NCSM 30000 from Pungo River Formation, Lee Creek Mine, Beaufort County, North Carolina, USA; (k)–(n) NCSM 30012 from Pungo River Formation, Lee Creek Mine, Beaufort County, North Carolina, USA; (o)–(r) MUSM 3238 from Chilcatay Formation, Ica, Peru; (s)–(v) KPM-NNV735, Oi Formation of Ichishi Group, Tsu City, Mie Prefecture; (w)–(y) Sketch of ‘Otodus sp.’ illustrated by Hasegawa and Uyeno (1967, plate 21, figure 1(a)–(c)); (z) Sketch of four teeth of ‘Lamna sp.’ illustrated by Renz (2009:158). Orientations: lingual view = (a), (g), (k), (o), (s), (w), and (z); labial view = (b), (h), (l), (p), (t), and (x); mesial view = (c), (i), (m), (q), and (u); distal view = (d) and (y); apical view = (e); basal view = (f), (j), (n), (r), and (v). All scale bars = 1 cm. Historical Biology 5

Materials MUSM 3238 (Figure 2(o)–(r)) is a complete tooth that measures 42.5 mm in total height and 34.0 mm in total width. The Holotype crown is slightly inclined distally and measures 33.2 mm in UCMP 112146, complete tooth (Figure 2(a)–(f)) from UCMP height and 30.5 mm in width, including the labial tooth neck Locality V6916 (Pyramid Hill Upper Bed), Pyramid Hill Sand present in the specimen as well as the lateral cusplets. Relative Member (early Miocene; Saucesian; Aquitanian) of the Jewett to other specimens except NCSM 30012, its lateral cusplets are Sand in Kern County, California, USA (Figure 1(a); detailed comparatively small with respect to the size of the main cusp. locality information available at UCMP; see below for additional KPM-NNV735 (Figure 2(s)–(v)) is a nearly complete tooth geographic and stratigraphic discussion). but shows small chipping along the cutting edges and apex of the crown and parts of the root. It measures 21.7 mm in estimated Additional material total height and 17.9 mm in total width. The crown is slightly NCSM 30000, nearly complete tooth (Figure 2(g)–(j)) from inclined distally and measures 17.1 mm in estimated height and Pungo River Formation, Lee Creek Mine, Beaufort County, 16.8 mm in width, including the labial tooth neck present in North Carolina, USA (same specimen described by Chandler the specimen as well as the lateral cusplets. Compared to other (ed.) 2015 as ‘Brachycarcharias sp.? – 21 mm’; detailed local- specimens of this species described here, KPM-NNV735 has the ity information available at NCSM); NCSM 30012, incomplete most pronounced lingual protuberance and deeply incised basal tooth (Figure 2(k)–(n)) from Pungo River Formation, Lee Creek root concavity. Mine, Beaufort County, North Carolina, USA (same specimen described by Chandler (ed.) 2015 as ‘Brachycarcharias sp.? – 45 mm’; detailed locality information available at NCSM); Additional records MUSM 3238, nearly complete tooth (Figure 2(o)–(r)) from A taxon conspecific to Megalolamna paradoxodon gen. nov. et Chilcatay Formation, Ica, Peru; KPM-NNV735, nearly com- sp. nov. was reported at least as early as 1967 when Hasegawa plete tooth (Figure 2(s)–(v)) from Mitsugeno Shaly Sandstone and Uyeno (1967, p. 116, plate 21, figure 1a–c) illustrated a Member of lower Miocene Oi Formation of Ichishi Group in Tsu 40.0-mm-tall tooth they referred to ‘Otodus sp.’ (Figure 2(w)– City, Mie Prefecture, Japan (same specimen described by Tanaka (y)) from the sandstone-dominant O’oshimojo Formation of 2013 as ‘Lamnidae gen. et sp. indet.’). the Miocene Tomikusa Group in Anan City, Nagano Prefecture, Japan (for stratigraphy, see Tanaka & Chinzei 1967). The tooth Description may be housed in the Anan City Fossil Museum, but we were not

able to confirm its exact whereabouts. A paleomagnetism study UCMP 112146 (Figure 2(a)–(f)) is a nearly complete tooth but indicates that the O’oshimojo Formation is about 18 Ma, which shows slight rounding from taphonomic abrasion. It measures is late early Miocene (Sako & Hoshi 2014), or mid-Burdigalian 28.3 mm in total height and 23.8 mm in total width. The crown in age. is slightly inclined distally and measures 22.1 mm both in height Renz (2009, p. 158) presented a photograph of four fossil teeth and width, including the labial tooth neck present in the speci- labeled ‘Lamna sp.’ from ‘Ica region, West Bank of the Ica River, men as well as the lateral cusplets. The basal crown (tooth neck) Chilcatay Formation.’ These teeth (Figure 2(z)) are most certainly ledge on the labial side is pronounced in this specimen. of Megalolamna paradoxodon gen. nov. et sp. nov. Those four NCSM 30012 (Figure 2(g)–(j)) has a chipped crown tip and a teeth are in a private collection, but MUSM 3238 described in damaged mesial root lobe tip, otherwise a nearly complete tooth. this paper (Figure 2(o)–(r)) supports the occurrence of the taxon It measures 21.0 mm in preserved total height, about 22.0 mm from the Chilcatay Formation in Ica, Peru. in estimated total height, and 18.0 mm in total width. The crown There are two other previously published accounts of the is slightly inclined distally and measures 17.5 mm both in esti- same taxon in literature. One is that of Tanaka (2013, p. 99) mated height and width. The tooth neck is present but not well who described the taxon as ‘Lamnidae gen. et sp. indet.’ The delineated in the specimen. The lateral cusplets are triangular other account is represented by two teeth of ‘Brachycarcharias and prominent. The mesial and distal root lobes are relatively sp.?’ illustrated by Chandler (ed.) (2015, p. 49). Their materials short compared to those in other specimens. are formally described in this present paper as KPM-NNV735 NCSM 30012 (Figure 2(k)–(n)) is an incomplete tooth, miss- (Figure 2(s)–(v)) and NCSM 30000 (Figure 2(g)–(j)) and 30012 ing the distal root lobe along with the distal lateral cusplet. The (Figure 2(k)–(n)). tooth measures 45.0 mm in total height, but its total width is uncertain due to the damage. The crown is nearly symmetrical Taxonomic remarks and measures 38.8 mm in height. The mesial half of the labial crown base strongly slants basally so that the apex of the mesial Teeth of the new taxon, Megalolamna paradoxodon gen. nov. lateral cusplet is situated below the center of the main cusp base. et sp. nov., were previously described as Otodus sp., Lamna sp., The mesial lateral cusplet is distinct but small and is directed api- Lamnidae gen. et sp. indet., or a possible Brachycarcharias sp. comesially. The lingual tooth neck is well preserved, delineated (see synonymy list above). The new taxon does not belong to by a thin enameloid band. The crown base on the labial side is Brachycarcharias because root lobes have a rounded tip and the marked by a ledge-like narrow tooth neck. The lingual root pro- basal concavity between the lobes delineate a moderately tight tuberance is robust and exhibits two nutritive pores. The broken U-shaped curve, unlike teeth of Brachycarcharias that exhibit root surface shows no pulp cavity, indicating its osteodentine pointed root lobe tips with a broad V-shaped basal concav- tooth histology. ity (e.g. see Cappetta 2012). Among the living taxa, teeth of 6 K. Shimada et al.

M. paradoxodon gen. nov. et sp. nov., or Megalolamna, resem- The mosaic of Cretalamna-Otodus characteristics makes the ble teeth of the lamnid genus Lamna. However, besides the fact taxon described in this paper morphologically unique and merits that the earliest geologic occurrence of Lamna is in the early its assignment to a new genus and species, Megalolamna para- Pliocene (Zanclean), Megalolamna is considered not to be doxodon gen. nov. et sp. nov. In fact, we interpret this taxon to closely related to Lamna. In contrast to teeth of Lamna that have represent a previously unrecognized clade that is sister to Otodus, smaller, more conical lateral cusplets which tend to be erect or and the clade uniting Megalolamna and Otodus is considered to are directed towards the main cusp (e.g. see Compagno 2002), be a sister to Cretalamna (see below for further phylogenetic dis- teeth of Megalolamna have more prominent lateral cusplets that cussion). There are some other non-otodontid lamniform genera are directed outward. in the fossil record with large teeth that possess a large main cusp Teeth of Megalolamna are most reminiscent to those of the with a pair of lateral cusplets and a robust bilobed root. Such taxa family Otodontidae, particularly Cretalamna and Otodus. The include Archaeolamna Siverson, Cardabiodon, Cretodus Sokolov, earliest record of Otodus is in the early Paleocene (Danian: and Pseudoisurus Glikman (e.g. see Cappetta 2012). These taxa Zhelezko & Kozlov 1999; Becker et al. 2011), and Megalolamna is are known exclusively from Cretaceous deposits, and thus these especially similar to the basal forms, such as O. naidini Zhelezko lamniforms are interpreted to have no direct phylogenetic affinity in Zhelezko and Kozlov, O. minor Leriche, and O. obliquus to Megalolamna paradoxodon gen. nov. et sp. nov. known only Agassiz (see below for further taxonomic discussion of Otodus). from the Miocene. In particular, their root morphology resembles that of M. paradoxodon gen. nov. et sp. nov. by exhibiting a rather robust lingual Discussion protuberance and a moderately broad but a rather deep basal root Paleobiology of Megalolamna paradoxodon gen. nov. et concavity with rounded root tips. However, its crown is not as sp. nov. robust as in Otodus spp., but rather more similar to Cretalamna. Contrary to Otodus, the fossil record of Cretalamna goes NCSM 30012 (Figure 2(k)–(n)) is the tallest tooth among the back deep in time to the Early Cretaceous (Albian: Siversson specimens of Megalolamna paradoxodon gen. nov. et sp. nov. et al. 2015). Siversson et al.’s (2015) recent taxonomic review of described in this paper. It has a crown height of 38.8 mm and Cretalamna resulted in erecting six additional species and plac- is nearly symmetrical, suggesting that it is likely an anterior ing C. gunsoni Siverson into a new genus Kenolamna Siversson, tooth (sensu Shimada 2002a). In modern macrophagous lam- Lindgren, Newbrey, Cederström, and Cook. Although the taxo- niforms, the second lower anterior tooth (a2) row generally nomic validity of C. pachyrhyza Herman, and C. lata (Agassiz), contains the tallest teeth in the mouth (Shimada 2002a), and is questionable (Siversson et al. 2015), the following 11 species conservative estimations about the body size of M. paradox- of Cretaceous Cretalamna are considered to be valid: C. appen- odon gen. nov. et sp. nov. are possible by applying the crown diculata Agassiz; C. biauriculata (Wanner); C. borealis Priem; height of 38.8 mm to known quantitative relationships between C. catoxodon Siversson, Lindgren, Newbrey, Cederström, and the crown height (CH) of the a2 and total body length (TL) in Cook; C. deschutteri Siversson, Lindgren, Newbrey, Cederström, the following modern macrophagous lamniforms: Mitsukurina and Cook; C. ewelli Siversson, Lindgren, Newbrey, Cederström, owstoni Jordan (Shimada & Seigel 2005, table 1) giving an esti- and Cook; C. gertericorum Siversson, Lindgren, Newbrey, mation of approximately 5.6 m TL, Carcharias taurus Rafinesque Cederström, and Cook; C. hattini Siversson, Lindgren, Newbrey, (Shimada 2004/2005) 3.8 m TL, Alopias vulpinus (Bonnaterre) Cederström, and Cook; C. maroccana (Arambourg); C. niger- (Shimada 2006) 19.5 m TL, Lamna nasus (Bonnaterre) (Chavez iana (Cappetta); and C. sarcoportheta Siversson, Lindgren, et al. 2012, table 1) 7.2 m TL, Isurus oxyrinchus Rafinesque Newbrey, Cederström, and Cook. Cretalamna appendiculata is (Shimada 2002b, table 1) 3.7 m TL, and Carcharodon carcha- also reported from Cenozoic deposits (e.g. Vasquez & Pimiento rias (Linnaeus) (Shimada 2003, table 1) 5.1 m TL. Although 2014), but the validity of the species in the Cenozoic is question- the exact body form and the relationship between the body size able (see Siversson et al. 2015). There are two other Cenozoic and tooth size are uncertain for Megalolamna paradoxodon gen. species referred to Cretalamna, C. aschersoni (Stromer) and C. nov. et sp. nov., its estimated TL of 19.5 m based on A. vulpinus twiggsensis (Case). Cretalamna twiggsensis is a more commonly is unrealistic. The exceptionally high estimated value is due to reported species and is known from the Eocene of Georgia, the fact that the caudal fin in A. vulpinus is as long as its body USA (Priabonian; Case 1981), Egypt (Priabonian; Adnet et al. and that the species has comparably small teeth in the mouth 2011), and Uzbekistan (Lutetian–Bartonian; Malyshkina & Ward (e.g. Compagno 2002). If A. vulpinus is excluded, the remaining 2016). Underwood et al. (2011) also described this species from five modern lamniform taxa give a range of 3.7–7.2 m TL with the middle–late Eocene (Lutetian–Priabonian) of Egypt, but the median and average of both about 5.1 m TL. The minimum placed it in the genus Brachycarcharias Cappetta and Nolf. In conservatively estimated TL of 3.7 m for the Megalolamna indi- fact, there is increased suspicion that this species may indeed vidual represented by NCSM 30012 is not unreasonable given not belong to Cretalamna (Malyshkina & Ward 2016). The only that some extinct and extant lamniforms are known to reach, other described Cenozoic species of Cretalamna, C. aschersoni, is or exceed, 3.7 m TL, such as Cretoxyrhina mantelli (Agassiz) reported from the upper Eocene (Priabonian) of Egypt (Cappetta (Shimada 1997, 2008), Cardabiodon ricki Siverson (Newbrey et 2012). However, although they are not as robust as those of al. 2015), Otodus megalodon (Agassiz) (Pimiento & Balk 2015), Otodus, the crowns of C. aschersoni are mesiodistally broad and Mitsukurina owstoni, Odontaspis ferox (Risso), Megachasma pela- its lateral cusplets tend to come in more than one pair, unlike gios Taylor, Compagno and Struhsaker, A. superciliosus (Lowe), teeth of Megalolamna. A. vulpinus, Cetorhinus maximus (Gunnerus), I. oxyrinchus, Historical Biology 7

I. paucus Guitart, Carcharodon carcharias, and possibly L. ditropis of M. paradoxodon gen. nov. et sp. nov. was of ‘grasping-’ or Hubbs and Follett and L. nasus (Compagno 2002). ‘tearing-type.’ However, lateral teeth, particularly those located Including Hasegawa and Uyeno’s (1967) specimen from the distally, have a shorter, more broader crown with well-marked O’oshimojo Formation in Nagano Prefecture, Japan (Figure cutting edges, indicating that the dentition likely had a ‘cutting’ 2(w)–(y)), Megalolamna paradoxodon gen. nov. et sp. nov. is so function towards the corners of its mouth. If so, with its esti- far known from five different localities (see above). A common mated TL of at least 3.7 m (see above), the diet of M. paradoxodon lithologic characteristic among the five localities is sandy sed- gen. nov. et sp. nov. could have included relatively large prey, such iment generally interpreted to represent shallow-water, shelf- as medium-sized [ca. 0.5–1 m] fishes, captured by the use of its type, coastal environments (see Olson 1988 for the Pyramid Hill anterior teeth and cut by the distal portion of its dentition to a Sand of California; Miller 1982 for the Pungo River Formation of size suitable for ingestion. North Carolina; Dunbar et al. 1990 for the Chilcatay Formation of Peru; Tanaka 2013 for the Mitsugeno Shaly Sandstone of Japan; Taxonomy of otodontid genera and Tanaka & Chinzei 1967 for the O’oshimojo Formation of Japan). Geographically, it is found along the Pacific (Japan, The otodontid taxonomy has been in flux largely due to the intro- California, and Peru) and western Atlantic (North Carolina) duction of multiple generic names aimed to include the iconic coasts. It is noteworthy that the taxon is found in the mid-latitu- fossil megathoothed species, megalodon, such as Carcharocles dinal zones in both Northern (Japan, California, North Carolina) Jordan and Hannibal, Procarcharodon Casier, and Megaselachus and Southern (Peru) Hemispheres (Figure 1). However, whether Glikman. Zhelezko and Kozlov (1999) considered many of the lack of the fossil record in the equatorial and high-latitude these ‘megalodon-clade genera’ not to merit a genus status and regions is biological (e.g. anti-tropical and anti-polar distribu- placed them as subgenera under the genus Otodus Agassiz. Many tions) or simply a sampling matter is uncertain especially because subsequent workers have continued to refer megatoothed forms the fossil record of the species is too scarce and sporadic. with serrated teeth (e.g. angustidens, auriculatus, chubutensis, Dentitions of macrophagous (= non-planktivorous) lam- megalodon, and sokolovi) to those traditional genera (e.g. Ehret niform sharks exhibit heterodonty in which distinct tooth et al. 2012; Laurito et al. 2014; Pimiento & Balk 2015; Kriwet types, such as anterior teeth, intermediate teeth, and lateral et al. 2016), whereas some others began to assign megalodon and teeth, are generally recognized (Shimada 2002a). Most teeth its closely allied species with serrated teeth to Otodus (Adnet of Megalolamna paradoxodon gen. nov. et sp. nov. are relatively et al. 2010; Underwood et al. 2011; Zalmout et al. 2012; see below tall, and their main cusp inclinations range from nearly sym- for further discussion). However, following Zhelezko and Kozlov

metrical to gently inclined or curved distally (Figure 2(a)–(y)). (1999), Cappetta (2012) in particular strongly advocated the use Similar to the largest tooth illustrated by Renz (2009; left-most of subgenera which led the family Otodontidae to include only tooth in Figure 2(z)), the most symmetrical tooth, NCSM 30012 two genera, Otodus and Parotodus Cappetta 1980. Subsequently, (Figure 2(k)–(n)), also represents the largest specimen in our Siversson et al. (2015) transferred Cretalamna, which was com- samples, and it is interpreted to be an anterior tooth. The other monly placed in the family Cretoxyrhinidae, to Otodontidae specimen from North Carolina, NCSM 30000 (Figure 2(g)–(j)), (see also Corral et al. 2016), and they also added a new genus and the holotype (UCMP 112146; Figure 2(a)–(f)) as well as a Kenolamna to the family. Therefore, Otodontidae currently tooth described by Hasegawa and Uyeno (1967, figure 2(w)– consists of four genera, Cretalamna, Kenolamna, Otodus, and (y)) have a tall crown that is slightly inclined or curved distally Parotodus, chronostratigraphically extending from the Early and are interpreted to represent mesially located lateral teeth, Cretaceous (Albian) to the Pliocene (Cappetta 2012; Siversson if not anterior teeth. KPM-NNV735 (Figure 2(s)–(v)) has the et al. 2015), although some have suggested the possibility that shortest crown among our examined samples, but even shorter, Parotodus may not belong to the family (e.g. Iserbyt & De more distally inclined or curved crowns, that are indicative of Schutter 2012 who listed Parotodus as ‘incertae sedis’). distally-located lateral teeth, are known to occur in M. para- Some workers have begun to consider taxa of the ‘megalo- doxodon gen. nov. et sp. nov. (e.g. three smallest teeth in Figure don-clade’ to belong to the genus Otodus (e.g. Andrianavalona et 2(z)). Although whether or not the species had one or more rows al. 2015; Malyshkina & Ward 2016). However, the previously used of ‘symphysial teeth’ and ‘intermediate teeth’ (sensu Shimada ‘megalodon-clade genera,’ such as Megaselachus and Carcharocles, 2002a) is unknown, all known teeth of M. paradoxodon gen. continue to be used in literature to date (e.g. Ehret & Ebersole nov. et sp. nov. (Figure 2) show a nearly continuous series of 2014; Laurito et al. 2014; Carrillo-Briceño et al. 2015; Pimiento tooth morphologies from tall and symmetrical teeth to short & Balk 2015; Pimiento et al. 2016). We note here that not using and distally inclined teeth without any decisive variation that any of those non-Otodus genera for the megalodon-clade taxa would indicate the difference between upper and lower teeth. can be justified on the basis of systematic principles. Figure 3 Therefore, the fossil shark likely exhibited disjunct monognathic shows two alternative topologies of the interrelationships among heterodonty (see Welton & Farish 1993). Otodus spp., Carcharocles spp., and Parotodus spp., where three Bony fishes are a common diet for most extant macrophagous species of Otodus accepted by Cappetta (2012), O. naidini, O. lamniforms (Compagno 2002). Because Megalolamna paradox- minor, and O obliquus, are explicitly arranged according to their odon gen. nov. et sp. has a dentition that is rather generalized in stratigraphic occurrences (note: for the purpose of this discus- form for macrophagous lamniforms, there is no reason to con- sion, other ‘megalodon-clade genera,’ such as Procarcharodon and sider that the species had a specialized diet. Thus, it likely fed on Megaselachus, are considered congeneric with Carcharocles in bony fishes. With a tall, relatively narrow main cusp in anterior Figure 3). Whereas the exact systematic position of Parotodus is teeth, this dental condition would indicate that the dentition uncertain (see above), O. obliquus and Carcharocles are depicted 8 K. Shimada et al.

supporting Zhelezko and Kozlov (1999) and Cappetta’s (2012) taxonomic treatment that Otodus includes taxa traditionally placed under Carcharocles. It should be noted that Parotodus can be retained as a valid genus in the scenario depicted in Figure 3(b), but not in the case of Figure 3(a). Whereas the traditional otodontid affinity ofParotodus remains questionable (see above), for the purpose of this paper, the genus Otodus is assumed to include taxa previously referred to Carcharocles for the remaining discussion. Another otodontid genus, Cretalamna, has traditionally been viewed as the ancestral stock of many lamniform lineages including the megalodon-clade taxa (e.g. Applegate & Espinosa- Figure 3. Phylogenetic hypotheses showing Otodus non-monophyly (included Arrubarrena 1996; Mas 2003). Along with Kenolamna, its recent taxa are those recognized by Cappetta 2012; see text for discussion). (a) polyphyletic Otodus if Parotodus is considered to be sister to ‘O. obliquus + Carcharocles’; (b) taxonomic transfer from Cretoxyrhinidae to Otodontidae paraphyletic Otodus if O. obliquus and Carcharocles are considered to be sister. (Siversson et al. 2015) further reflects the idea that the origin of the Otodus linage is rooted in Cretalamna. The geologically oldest Otodus is known from the early Paleocene (Danian: Zhelezko & Kozlov 1999; Becker et al. 2011), so its divergence from Cretalamna likely took place soon after the Cretaceous- Paleogene mass extinction event. With this assumption, Figure 4(a) shows the interrelationships of otodontid taxa through time based on the present fossil record. Although the exact divergence time between Kenolamna and Cretalamna is uncertain, and although the expressions ‘Cretaceous Cretalamna’ and ‘Cenozoic Cretalamna’ are appreciably over-simplified for the purpose of our present discussion, it is aimed to demonstrate that, if the Otodus clade emerged from the Cretalamna clade, Cretalamna is considered to be a paraphyletic genus that excludes Otodus. If

we were to consider a Cretalamna monophyly, then the divergence time between Cretalamna and Otodus would have been much deeper in time—i.e. sometime during the Late Cretaceous (Figure 4(b))—which is not congruent with the current fossil record of Otodus. There are two obvious solutions to the ‘Cretalamna paraphyly’ problem. One is to accept that Cretalamna is a paraphyletic taxon, and continue its usage as is. Another possibility is equivalent to the ‘first strategy’ of Brummitt (1997) to eliminate a paraphyly which is to ‘sink’ Cretalamna into the genus Figure 4. Schematic illustration showing interrelationships of three otodontid Otodus that has the nomenclatorial priority. However, neither genera Kenolamna, Cretalamna, and Otodus (Whereas the otodontid affinity of Parotodus is questionable [see text], Otodus here includes taxa formerly of these solutions sits well because a paraphyletic taxon hin- assigned to Carcharocles). (a) phylogenetic hypothesis with geologic time scale ders elucidation of the exact evolutionary history of that and showing interrelationships of otodontid genera with Cretalamna paraphyly; its closely related taxa (e.g. Hennig 1966; Schwenk 1994) and (b) phylogenetic hypothesis showing scenario with Cretalamna monophyly based on presently known otodontid genera (single asterisk [*] indicates node an overly inclusive monophyletic genus with multiple distinc- with divergence time problem); (c) phylogenetic hypothesis showing possible tive forms may obscure the complexity of evolutionary history. systematic position of Megalolamna paradoxodon gen. nov. et sp. nov. The ‘Cretalamna paraphyly’ problem is an excellent example of that allows Cretalamna monophyly (double asterisks [**] indicate node with geochronologically congruent divergence time). a well-known fact that the recognition of paraphyletic taxa is ‘inevitable’ and generally irreconcilable when Linnaean taxa are superimposed on a phylogenetic tree (e.g. Brummitt 1997). In as sisters in both Figure 3(a) and (b). When Parotodus is consid- fact, we also note that the ‘Otodus paraphyly’ problem discussed ered to be sister to ‘O. obliquus + Carcharocles’, the genus Otodus earlier (Figure 3(b)) is actually the same situation where we used is found to be polyphyletic that contains two unaccounted line- it to consider Otodus as a monophyletic assemblage by includ- ages Carcharocles and Parotodus (Figure 3(a)). When Parotodus is ing taxa traditionally classified to Carcharocles. We recommend regarded as the basal-most clade among the three genera consid- this taxonomic treatment of Otodus given that the total number ered, the genus Otodus is found to be paraphyletic that excludes of recognized species in the clade is small and that their fossil Carcharocles (Figure 3(b)). Therefore, either scenario indicates record suggests largely anagenetic-type evolution where most that the traditional usage of the genus Otodus is non-monophy- of them represent different chronospecies (Zhelezko & Kozlov letic. In order to consider Otodus as a monophyletic assemblage 1999; Cappetta 2012). and a valid genus, Carcharocles (and also Parotodus in the case The question is whether or not one can retain Cretalamna of Figure 3(a)) must be regarded as part of the Otodus clade, as a monophyletic genus without taxonomically ‘sinking’ it into Historical Biology 9

Otodus. One possibility is to erect a new genus for a Cretalamna Science). We appreciate comments and suggestions made by C. Pimiento species that would represent a sister to Otodus, which would and an anonymous reviewer that significantly improved the quality of this essentially be equivalent to the ‘second strategy’ of Brummitt paper. Various support provided by the Department of Environmental Science and Studies and Department of Biological Sciences at DePaul (1997) that was presented as a possible solution to eliminate a University is appreciated. paraphyly. However, the discovery of Megalolamna paradoxodon gen. nov. et sp. nov. that exhibits a mosaic of Cretalamna- Disclosure statement Otodus characteristics can conveniently represent a unique clade that is sister to Otodus without the need of splitting existing No potential conflict of interest was reported by the authors. Cretalamna species (Figure 4(c)). This systematic arrangement concomitantly allows both genera, Cretalamna and Otodus, to References be monophyletic, and unlike the scenario shown in Figure 4(b), Adnet S, Cappetta H, Elnahas S, Strougo A. 2011. A new Priabonian the origination time of the Cretalamna clade can be placed in chondrichthyans assemblage from the western desert, Egypt. the Cretaceous that is congruent with the fossil record. However, Correlation with the Fayum oasis. J Af Earth Sci. 61:27–37. the recognition of M. paradoxodon gen. nov. et sp. nov. as a sister Adnet S, Cappetta H, Tabuce R. 2010. A Middle-Late Eocene vertebrate to Otodus (Figure 4(c)) does not come free of problems. One fauna (marine fish and mammals) from southwestern Morocco; notable paradox that emerges with this scenario is a 43-mil- preliminary report: age and palaeobiogeographical implications. 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Tanaka T. 2013. Fossil elasombranchs from the Ichishi Group of Lower fauna from the Uitpa Formation in northern Colombia. Among Miocene in Mie Prefecture, Japan. J Geosci [Chigaku Kenkyu]. 61:93– the specimens described from the fauna is a tooth referred to as 116 (in Japanese). “Lamniformes gen. et sp. indet.” (Carrillo-Briceño et al. 2016, Underwood CJ, Ward DJ, King C, Antar SM, Zalmout IS, Gingerich PD. 2011. Shark and ray faunas in the Middle and Late Eocene of the Fayum p. 86, fig. 4.16, 4.17). We note that the morphology and size area, Egypt. Proc Geologists’ Asso. 122:47–66. of the tooth as well as its chronostratigraphic occurrence are Vasquez S, Pimiento C. 2014. Sharks and rays from the Tonosi Formation consistent with teeth of Megalolamna paradoxodon gen. nov. (Eocene of Panama). Central Am J Geol. 51:165–169. et sp. nov. described here. Carrillo-Briceño et al. (2016) noted Ward LW. 2008. Synthesis of paleontological and stratigraphic that the shark may belong either to a previously undescribed investigations at the Lee Creek Mine, Aurora, N.C. (1958–2007). In: Ray CE, Bohaska DJ, Koretsky IA, Ward LW, Barnes LG, editors. Geology taxon closely related to Otodontidae or to an as yet unnamed and paleontology of the Lee Creek Mine, North Carolina, IV. Virginia taxon of Lamnidae, whereas we maintain our interpretation that Mus Nat Hist Spec Pub 14; p. 325–436. M. paradoxodon gen. nov. et sp. nov. is an otodontid. Although Welton BJ. 2015. A new species of late Early Miocene Cetorhinus they did not expand on their claim, Carrillo-Briceño et al. (2016, (Lamniformes: Cetorhinidae) from the Astoria Formation of Oregon, p 86) stated that the taxon is also present in Europe (Austria, and coeval Cetorhinus from Washington and California. Nat Hist Mus Los Angeles Co Cont Sci. 523:67–89. Switzerland, Germany, and Sardinia) as well as in Peru and Welton BJ, Farish RF. 1993. The collector’s guide to fossil sharks and rays along the east coast of North America. In particular, they wrote from the Cretaceous of Texas. Lewisville (TX): Before Time; 204 p. that the taxon is “abundant” in the Miocene Calvert Formation Zalmout ISA, Antar MSM, Shafy EA-E, Metwally MH, Hatab E-BE, of Maryland (p. 86). We are skeptical of this particular record. Gingerich PD. 2012. Priabonian sharks and rays (Late Eocene: Carrillo-Briceño et al.’s (2016) locality in Colombia is important Neoselachii) from Minqar Tabaghbagh in the western Qattara Depression, Egypt. Univ Michigan Mus Paleont Cont. 32:71–90. because it adds another geographic record for M. paradoxodon Zhelezko VI, Kozlov VA. 1999. Elasmobranhii i biostratigraphia paleogena gen. nov. et sp. nov., and more significantly, because it substan- Zauralia i Srednei Asii [Elasmobranchii and Palaeogene biostratigraphy tiates the presence of the taxon in the tropics—a point that was of Transural and Central Asia]. Materialy po stratigrafii i paleontologii not resolved in our paper. Urala. 3: 324 p.

Notes added at proof Reference Carrillo-Briceño JD, Argyriou T, Zapata V, Kindlimann R, Jaramillo C. 2016. After this present manuscript went to its editorial process, we A new early Miocene (Aquitanian) Elasmobranchii assemblage from the learned about a paper written by Carrillo-Briceño et al. (2016) La Guajira Peninsula, Colombia. Ameghiniana 53:77–99. doi: http:// that described an early Miocene (Aquitanian) elasmobranch dx.doi.org/10.5710/AMGH.26.10.2015.2931

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