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DePaul Discoveries

Volume 1 Issue 1 Article 5

2012

Cranial Musculature in Extant , Pseudocarcharias kamoharai (: Pseudocarchariidae) and its Evolutionary Implications

Ikechukwu B. Achebe DePaul University, [email protected]

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Recommended Citation Achebe, Ikechukwu B. (2012) "Cranial Musculature in Extant , Pseudocarcharias kamoharai (Lamniformes: Pseudocarchariidae) and its Evolutionary Implications," DePaul Discoveries: Vol. 1 : Iss. 1 , Article 5. Available at: https://via.library.depaul.edu/depaul-disc/vol1/iss1/5

This Article is brought to you for free and open access by the College of Science and Health at Via Sapientiae. It has been accepted for inclusion in DePaul Discoveries by an authorized editor of Via Sapientiae. For more information, please contact [email protected]. Cranial Musculature in Extant Crocodile Shark, Pseudocarcharias kamoharai (Lamniformes: Pseudocarchariidae) and its Evolutionary Implications

Acknowledgements Faculty Advisor: Dr. Kenshu Shimada, Department of Biological Sciences & Department of Environmental Science and Studies

This article is available in DePaul Discoveries: https://via.library.depaul.edu/depaul-disc/vol1/iss1/5 Achebe: Cranial Musculature in Extant Crocodile Shark, Pseudocarcharias kamoharai (Lamniformes: Pseudocarchariidae) and its Evolutionary Implications DEPAUL DISCOVERIES (2O12)

Cranial Musculature in Extant Crocodile Shark, Pseudocarcharias kamoharai (Lamniformes: Pseudocarchariidae) and its Evolutionary Implications

Ikechukwu B. Achebe* Department of Biological Sciences

ABSTRACT The crocodile shark, Pseudocarcharias kamoharai, is a small lamniform shark that occupies tropical oceans worldwide. Here, its cranial musculature and ligaments associated with jaw suspension are described in detail for the first time. Anatomical data extracted from this study is combined with data from existing literature, and mapped onto previously proposed phylogenetic trees examining the evolutionary pattern of jaw through lamniform phylogeny. Results show that the evolution of characters associated with jaw suspension is more parsimonious in the morphology-based phylogenetic tree than in the molecular-based tree. Additionally, the evolutionary scenario of lamniform jaws is found to be more complex than previously hypothesized regardless of the tree used.

INTRODUCTION sandtiger, thresher, basking, mako, and white Sharks (: ) are efficient (Compagno, 2002). The crocodile shark, Pseudocarcharias aquatic predators with a variety of feeding strategies, kamoharai (Matsubara) (Fig. 1a) is the smallest (up to ca. including ram, suction, bite, and filter to capture prey 1 m TL [total length]) of all lamniform and is (Motta, 2004). The morphology of jaw musculature and found in epipelagic zones of tropical oceans worldwide jaw suspension play an important role in determining (Compagno, 2002). Despite its relatively wide geographic the extent to which a shark can effectively execute a distribution, its biology remains poorly understood. This particular feeding behavior, such as gouging, crushing, paper describes the cranial musculature of P. kamoharai and head shaking. Whereas bite feeding is interpreted in detail and discusses its evolutionary and ecological to be the ancestral mechanism chondrichthyans use to implications. catch prey, a number of evolutionary modifications to

the feeding apparatus have taken place through shark MATERIALS AND METHODS phylogeny (e.g., Wilga, 2005). Yet, the evolution of shark Three preserved specimens of P. kamoharai were feeding behaviors influenced by the anatomy of their jaw examined: 1) FMNH 117474, 1,011-mm-TL male from the suspension is still not entirely understood (Motta, 2004). Hawaiian water, housed in the Field Museum of Natural History in Chicago, Illinois, 2) BPBM 37113, 1,080-mm-TL Lamniformes is a monophyletic group of sharks female from the Hawaiian water, housed in the Bernice P. represented by 15 modern species, such as the goblin, Bishop Museum in Honolulu, , and 3) LACM 45857, 922-mm-TL female from the Pacific of Mexico, * Faculty Advisor: Dr. Kenshu Shimada, Department of Biological Sciences housed in the Natural History Museum of Los Angeles, & Department of Environmental Science and Studies Author contact: [email protected]

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California. A Siemens Medical Systems’ SOMATOM orbital process of the palatoquadrate are absent. The Sensation® 64-slice computed tomography (CT) scanner palatonasal ligament is prominent and rope-like but is at the Children’s Memorial Hospital in Chicago, Illinois not accompanied by a cartilaginous rod. The epaxialis was used to image jaw muscles. However, CT images muscle extends posteriorly from the dorsoposterior could not separate small muscles apart, and thus a ‘peel surface of the neurocranium in which it loops around dissection’ was performed on the right side of the head the parietal fossa. The mid-lateral raphe extends from of FMNH 117474 and BPBM 37113 where the skin was the posterior end of Meckel’s cartilage to the midpoint transected and reflected to expose cranial musculature. of the quadratomandibularis muscles. The preorbitalis inserts to the posteroventral region of the nasal capsule. The study follows Wilga (2005) for muscle and ligament The quadratomandibularis superficial division is broad terminology. However, for skeletal terminology of jaw and occupies two-thirds of the quadrate process of the structures, a set of terms is used (Fig. 2) emended from palatoquadrate. The quadratomandibularis medial the usage by Maisey (1980), Shimada (2002), and Wilga division is a triangular and sheet-like muscle. The (2005). For example, Wilga (2005, fig. 3C, D) identified quadratomandibularis deep division originates from the ethmoid process on the palatoquadrate in between sheaths of cartilage on the mandible, and (mako shark) and (white shark), but the extends to the posterodorsal rim of the quadrate process projection is actually the dorsally inflated upper dental of the palatoquadrate. The quadratomandibularis ventral bulla. The dental bulla that houses enlarged mesially- division originates from the ventral margin of the mid- located teeth is common to all macrophagous lamniforms lateral raphe and inserts along the ventral posterior (Shimada, 2002), but the ethmoid process is absent margin of Meckel’s cartilage. The intermandibularis in Isurus and Carcharodon (this study). Wilga (2005) originates from the mid-ventral raphe to insert onto the notes the presence of ‘a small process’ on the dorsal quadratomandibularis ventral division. The cartilaginous surface of each palatoquadrate immediately lateral to intermandibular plates are teardrop-shaped, attach to the symphysis in nasus ( shark). This the mid-ventral raphe, and are located immediately process is called the mesial process and is unique to below the first and second lower lateral teeth. Muscles (Lamna, Isurus, and Carcharodon; Compagno, of the hyoid muscle plate insert at the posterior end 1990, Shimada, 2002, 2005). In summary, there are three of the lower dental bulla; the origin of these muscles types of dorsally-projected processes recognized on the however remains unclear. The levator hyomandibularis palatoquadrate of lamniforms: 1) the mesial process connects to the anterior margin of the quadrate process that connects to the palatonasal ligament, 2) the upper of the palatoquadrate and inserts into much of the dental bulla that makes no connection to any ligament or hyomandibula. The interhyoideus muscles originate from muscle, and 3) the ethmoid process that attaches to the the posterior end of the ceratohyal and the posterior edge ethmopalatine ligament. Whereas the orbital process is of Meckel’s cartilage. The interhyoideus muscles insert completely absent in all lamniforms as ‘non-orbitostylic onto the posterior end of the ceratohyal and Meckel’s sharks’ (Maisey, 1980; Wilga, 2005), no lamniform species cartilage immediately posterior to the intermandibularis possesses all three processes on one jaw. plate. The coracomandibularis is a massive muscle that originates at the coracoid bar and inserts between RESULTS the lower dental bulla. The coracohyoideus muscle is The following list describes the morphology of dense in character and runs immediately dorsal to the ligamentous and musculoskeletal elements that are coracomandibularis. The coracoarcualis extends from involved in jaw suspension in Pseudocarcharias the mid-ventral coracoid bar to meet with the hypaxialis kamoharai (Fig. 1b–d): The ethmopalatine ligament and and pectoral fin muscles.

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DISCUSSION their study, Naylor et al.’s (2012, fig. 2.2) molecular-based Wilga (2005) (Fig. 3a) proposed an evolutionary scenario phylogenetic tree shows a sister relationship between of lamniform jaws using a phylogenetic tree that Cetorhinus and (Fig. 3d), unlike Martin et largely agreed with the first hypothesis of phylogenetic al.’s molecular-based tree (Fig. 3c). The mapping of the interrelationships of all extant lamniform species ligamentous, myological, and skeletal data on to Naylor proposed by Compagno (1990) (Fig. 3a). Although et al.’s (2012) tree yields a set of evolutionary reversals the lamniform monophyly is strongly supported, the in the Carcharias , and thus is least parsimonious. phylogenetic trees based on morphological data (Fig. In short, character evolution based on the morphology- 3b: Compagno, 1990; Shirai, 1996; Shimada, 2005) based tree (Fig. 3b) is the most parsimonious tree among are found to differ significantly from those based on the three trees (cf. Figs. 3c, d), followed by Martin et al.’s molecular data (Fig. 3c, d: Naylor et al., 1997, 2012; Martin (Fig. 3c) and then by Naylor et al.’s molecular-based tree et al., 2002). In particular, the morphology-based trees (Fig. 3d). Regardless, every presented scenario indicates show Alopias to represent a sister taxon to a clade that the evolution of jaw ligaments and muscles in uniting Cetorhinus and Lamnidae, and indicated that lamniforms is more complex than initially proposed by , Carcharias, , Pseudocarcharias, Wilga (2005). In particular, Wilga’s (2005) study did not and represent less derived taxa in the trees include Pseudocarcharias and Megachasma to show the compared to the clade uniting Alopias, Cetorhinus, and independent acquisition of an insertion of the levator Lamnidae (Fig. 3b). This tree topology contrasts with hyomandibularis to the palatoquadrate (Character 4 practically all molecular-based trees that include all in Fig. 3) and the loss of the ethmopalatine ligament lamniform genera. Alopias was consistently separated (Character 7 in Fig. 3) in Pseudocarcharias as well as from the clade comprising Cetorhinus and Lamnidae the loss of the palatonasal ligament in Megachasma and instead clustered with a clade uniting Odontaspis, (Character 9 in Fig. 3). Pseudocarcharias, and Megachasma (e.g., Naylor et al., 1997, 2012; Martin et al., 2002; Fig. 3c, d). The systematic Character mapping (Fig. 3a and 3b) offers some additional position of Carcharias remains uncertain, but Martin et evolutionary insights. For example, the evolution and al. (2002) and Naylor et al. (2012) showed that the genus loss of the ethmopalatine ligaments and ethmoid is closely allied to Cetorhinus and Lamnidae (Fig. 3c, d). processes of the palatoquadrate are tightly associated. In contrast, features related to the palatonasal ligament, The topological differences between morphology- such as the cartilaginous rod within the palatonasal based and molecular-based trees provide contrasting ligament and the mesial process of the palatoquadrate, evolutionary scenarios. Figure 3 shows a morphology- evolved independent of the ligament and one another. based tree (Fig. 3b) and two molecular-based trees (Fig. 3c, However, it is important to note that ligamentous and d) with anatomical structures involved in jaw suspension musculoskeletal elements have not been investigated for mapped on them based on skeletal data presented by Odontaspis ferox, O. noronhai, and Cetorhinus maximus Shimada (2002) and ligamentous and myological data as well as a few other lamniform species, such as Alopias presented by Wilga (2005), Nakaya et al. (2008), and this pelagicus (pelagic ), A. superciliosus present study. Notably, the systematic disassociation of ( shark), and Lamna ditropis (salmon Alopias from a clade uniting Cetorhinus and Lamnidae shark). Therefore, it is possible that the evolution of these in the molecular-based trees (Fig. 3c, d) results in anatomical elements may be even more complex than additional steps to character evolution compared to shown in Figure 3a and 3b. the morphology-based scenario (Fig. 3b). Furthermore, besides the very unlikely ‘Alopias non-monophyly’ in

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ACKNOWLEDGEMENTS scanning and x-ray shooting of examined specimens. I thank the following individuals who were involved An immense gratitude is offered to K. Shimada whose in the acquisition, loan, or transportation of examined guidance and great inspirations helped propel this specimens: A. Y. Suzumoto (BPBM); M. A. Rogers, W. L. research. This project is supported by the Illinois Louis Smith, K. Swagel, M. W. Westneat, P. Willink (FMNH); J. Stokes Alliance for Minority Participation Grant that A. Seigel (LACM); S. J. Arceneaux, and R. L. Humphreys, is sponsored by the National Science Foundation, and Jr. Special thanks go to C. K. Rigsby, K. Gray, B. Karl, J. I thank V. Simek for handling the paper work. I also Hickey, A. Nicholas, and B. Reilly (Children’s Memorial thank the Department of Biological Sciences at DePaul Hospital, Chicago, Illinois) for assisting me with CT University for their continued support.

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Fig. 1. Head region of crocodile shark, Pseudocarcharias kamoharai (anterior to left). a, External

morphology (BPBM 37113 in lateral view). b, Computed tomography image showing anterior

extent of epaxial muscles and adjacent muscles (BPBM 37113 in dorsal view). c, Dissected

superficial cranial musculature (FMNH 117474 in lateral view; cf. Fig. 2c). d, Line drawing

showing identified superficial cranial musculature (FMNH 117474 in lateral view; cf. Figs. 1c,

2c). Abbreviations: BC, branchial constrictors; EP, epaxialis; LH, levator hyomandibularis; LP,

levator palatoquadrati; MC, Meckel’s cartilage; NC, nasal capsule; O, orbit; PF, parietal fossa;

PO, preorbitalis; PQ, palatoquadrate; QMD, dorsal quadratomandibularis superficial division; Fig. 1. Head region of crocodile shark, Pseudocarcharias kamoharai (anterior to left). a, External

FIGURE 1 QMDm, dorsal quadratomandibularis medial division; QMV, ventral quadratomandibularis, RC, morphology (BPBM 37113 in lateral view). b, Computed tomography image showing anterior rostral cartilage. Bar = 5 cm. Head region of crocodile shark, Pseudocarcharias kamoharaiextent (anterior of epaxial to left). muscles a, External and adjacent morphology muscles (BPBM (BPBM 37113 37113 in in lateral dorsal view). view). b, c Computed, Dissected tomography image showing anterior extent of epaxial muscles and adjacent muscles (BPBM 37113 in dorsal view). c, Dissected superficial cranial superficial cranial musculature (FMNH 117474 in lateral view; cf. Fig. 2c). d, Line drawing musculature (FMNH 117474 in lateral view; cf. Fig. 2c). d, Line drawing showing identified superficial cranial musculature (FMNH 117474 in lateral view; cf. Figs. 1c, 2c). Abbreviations: BC, branchial constrictors; EP,showing epaxialis; identified LH, levator superficial hyomandibularis; cranial musculature LP, levator (FMNH palatoquadrati; 117474 in lateral MC, view; Meckel’s cf. Figs. cartilage; 1c,

NC, nasal capsule; O, orbit; PF, parietal fossa; PO, preorbitalis;2c). PQ, Abbreviations: palatoquadrate; BC, branchialQMD, dorsal constrictors; quadratomandibularis EP, epaxialis; LH, superficial levator hyomandibularis; division; QMDm, LP, dorsal quadratomandibularis medial division; QMV, ventral quadratomandibularis, RC, rostral cartilage. Bar scale = 5 cm. levator palatoquadrati; MC, Meckel’s cartilage; NC, nasal capsule; O, orbit; PF, parietal fossa;

PO, preorbitalis; PQ, palatoquadrate; QMD, dorsal quadratomandibularis superficial division; Fig. 1. Head region of crocodile shark, Pseudocarcharias kamoharai (anterior to left). a, External QMDm, dorsal quadratomandibularis medial division; QMV, ventral quadratomandibularis, RC, — 65 — https://via.library.depaul.edu/depaul-disc/vol1/iss1/5rostral cartilage. Bar scale = 5 cm. 4 morphology (BPBM 37113 in lateral view). b, Computed tomography image showing anterior

extent of epaxial muscles and adjacent muscles (BPBM 37113 in dorsal view). c, Dissected

superficial cranial musculature (FMNH 117474 in lateral view; cf. Fig. 2c). d, Line drawing

showing identified superficial cranial musculature (FMNH 117474 in lateral view; cf. Figs. 1c, Fig. 1. Head region of crocodile shark, Pseudocarcharias kamoharai (anterior to left). a, External 2c). Abbreviations: BC, branchial constrictors; EP, epaxialis; LH, levator hyomandibularis; LP, morphology (BPBM 37113 in lateral view). b, Computed tomography image showing anterior levator palatoquadrati; MC, Meckel’s cartilage; NC, nasal capsule; O, orbit; PF, parietal fossa; extent of epaxial muscles and adjacent muscles (BPBM 37113 in dorsal view). c, Dissected PO, preorbitalis; PQ, palatoquadrate; QMD, dorsal quadratomandibularis superficial division; superficial cranial musculature (FMNH 117474 in lateral view; cf. Fig. 2c). d, Line drawing QMDm, dorsal quadratomandibularis medial division; QMV, ventral quadratomandibularis, RC, showing identified superficial cranial musculature (FMNH 117474 in lateral view; cf. Figs. 1c, rostral cartilage. Bar scale = 5 cm. 2c). Abbreviations: BC, branchial constrictors; EP, epaxialis; LH, levator hyomandibularis; LP, levator palatoquadrati; MC, Meckel’s cartilage; NC, nasal capsule; O, orbit; PF, parietal fossa;

PO, preorbitalis; PQ, palatoquadrate; QMD, dorsal quadratomandibularis superficial division;

QMDm, dorsal quadratomandibularis medial division; QMV, ventral quadratomandibularis, RC, rostral cartilage. Bar scale = 5 cm. Achebe: Cranial Musculature in Extant Crocodile Shark, Pseudocarcharias kamoharai (Lamniformes: Pseudocarchariidae) and its Evolutionary Implications DEPAUL DISCOVERIES (2O12) Achebe (Page 11)

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Fig. 2. Examples of lamniform jaws showing types of dorsally-directed projections on anterior

portion (palatine process) of palatoquadrate (upper jaw) and types of articulation they make to

Quadrate neurocranium (basedPalatine on Maisey,process 1980; Shimada, 2002; Wilga, 2005). a, Jaw specimen of process sandtiger shark, Carcharias taurus, in dorsal view showing dental bulla and ethmoid process on

left palatoquadrate (notes: this species lacks mesial process beneath palatonasal ligament; AMNH

79962SD housed in American Museum of Natural History, , New York). b, Jaw

specimen of porbeagle shark, Lamna nasus , in dorsal view showing mesial process and dental

FIGURE 2 bulla on left palatoquadrate (notes: palatonasal ligament that connected to mesial process is Examples of lamniform jaws showing types of dorsally-directed projections on anterior portion (palatine process) of palatoquadrate (upper jaw) and Fig. 2. Examples of lamniform jaws showing types of dorsally-directedtypes of articulation they make projections to neurocranium (basedon anterior on Maisey, 1980; Shimada, 2002; Wilga, 2005). a, Jaw specimen of sandtiger shark, Carcharias taurusremoved, in dorsal view in showingthis specimen; dental bulla and ethmoidthis species process on leftlacks palatoquadrate ethmoid (notes: process; this species lacks MCZ mesial 36258process beneath housed palatonasal in Museum of portion (palatine process) of palatoquadrate (upper jaw)ligament; and typesAMNH 79962SD of articulation housed in American they Museum make of Natural to History, New York, New York). b, Jaw specimen of porbeagle shark, Lamna nasus, in dorsal view showing mesial process and dental bulla on left palatoquadrate (notes: palatonasal ligament that connected to mesial process is removed inComparative this specimen; this species Zoology lacks ethmoid at process;Harvard MCZ 36258 University, housed in Museum Cambridge, of Comparative ZoologyMassachusetts). at Harvard University, c ,Cambridge, Computed neurocranium (based on Maisey, 1980; Shimada, 2002;Massachusetts). Wilga, 2005). c, Computed a, tomography Jaw specimen image of cranial of skeleton of crocodile shark, Pseudocarcharias kamoharai, in left lateral view showing position oftomography palatine and quadrate image processes of palatoquadrate cranial skeleton with dental bulla of as crocodile well as Meckel’s shark,cartilage (lower Pseudocarcharias jaw) with dental bulla (FMNH kamoharai 117474; cf. Fig. 1c,, in left sandtiger shark, Carcharias taurus, in dorsal view showingd). Bar scaledental = 2 cm. bulla and ethmoid process on lateral view showing position of palatine and quadrate processes of palatoquadrate with dental left palatoquadrate (notes: this species lacks mesial process beneath palatonasal ligament; AMNH bulla as well as Meckel’s cartilage (lower jaw) with dental bulla (FMNH 117474; cf. Fig. 1c, d). 79962SD housed in American Museum of Natural History, New York, New York). b, Jaw Bar scale = 2 cm. — 66 — Published by Via Sapientiae, 2012 5 specimen of porbeagle shark, Lamna nasus, in dorsal view showing mesial process and dental bulla on left palatoquadrate (notes: palatonasal ligament that connected to mesial process is removed in this specimen; this species lacks ethmoid process; MCZ 36258 housed in Museum of

Comparative Zoology at Harvard University, Cambridge, Massachusetts). c, Computed tomography image of cranial skeleton of crocodile shark, Pseudocarcharias kamoharai, in left lateral view showing position of palatine and quadrate processes of palatoquadrate with dental bulla as well as Meckel’s cartilage (lower jaw) with dental bulla (FMNH 117474; cf. Fig. 1c, d).

Bar scale = 2 cm. CRANIALDePaul MUSCULATUREDiscoveries, INVol. EXTANT 1 [2012], CROCODILE Iss. 1, SHARK Art. 5 Achebe (Page 12)

Fig. 3. Alternative phylogenetic hypotheses of extant lamniform sharks with mapping of

FIGURE 3 ligamentous and muscular characters (1–9) as well as skeletal characters (A–E) participating in Alternative phylogenetic hypotheses of extant lamniform sharks with mapping of ligamentous and muscular characters (1–9) as well asjaw skeletal suspension characters (A–E)(* = participating data based in on jaw Wilga,suspension 2005; (* = data ** based = data on Wilga,based 2005; on **Nakaya = data based et al., on Nakaya2008; et no al., 2008; no asterisk = ligament and muscle data based on this present study and skeletal data based on Shimada 2005). a, Wilga’s (2005) asterisk = ligament and muscle data based on this present study and skeletal data based on hypothesis about character evolution mapped onto morphology-based phylogenetic tree (Compagno 1990). b, hypothesis about character evolution mapped onto morphology-based phylogenetic tree (Compagno 1990) by combining data from Wilga (2005), Shimada 2005). a, Wilga’s (2005) hypothesis about character evolution mapped onto morphology- Nakaya et al. (2008), and this study. c, hypothesis about character evolution mapped onto Martin et al.’s (2002) molecular-based phylogenetic tree by combining data from Wilga (2005), Nakaya et al. (2008), and this study. d, hypothesis about character evolution mapped onto Naylor et al.’s (2012, fig. 2.2) molecular-based phylogenetic tree by combining data from Wilga (2005), Nakaya et al. (2008), and this study [notes: Alopias in Naylor et al.’s (2012) study was depicted as non-monophyletic where A. superciliosus (not depicted here) was clustered with a clade uniting Pseudocarcharias, Odontaspis, and Megachasma; numbers in gray box indicate characters with polarity reversal, where those features are suggested to be secondarily lost in the Carcharias clade].

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Wilga CD. 2008. Evolutionary divergence in the feeding mechanism of fishes. Acta Geol Polonica 58:113–120.

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