Perez et al.—Miocene sharks and rays from Lago Bayano, Panama
body size range of TL = 2.1–3m (Compagno, 1984). Teeth from the Chucunaque Formation and the Gatun Formation (CH = 3.7–13.7mm; Pimiento et al., 2013a) are smaller than those of Lee Creek. Negaprion brevirostris has been identified in the Miocene of Venezuela, Cuba, and Ecuador (Longbottom, 1979; Iturralde-Vinent et al., 1996; Aguilera and Rodrigues de Aguilera, 2001; MacPhee et al., 2003). Carrillo-Briceño et al. (2015a) reported two teeth attributed to N. brevirostris from the neritic Rio Indio facies, but no occurrences in the bathyal Piña Sandstone facies of the Chagres Formation. Extant individuals occur in tropical and temperate, estuarine and marine waters generally at depths of 0–92 m (Compagno, 1984; Kent, 1994). Negaprion brevirostris frequents mangrove fringes and coral reefs, but occasionally can be found in open ocean near surface waters for migration purposes (Compagno, 1984; Compagno et al., 2005).
Genus Rhizoprionodon Whitley, 1929
Type.—Carcharias (Scoliodon) crenidens Klunzinger, 1880 (Cappetta, 2012).
Rhizoprionodon sp. Figure 7.5–7.8
Occurrence.—STRI 290109, STRI 290116, and YPA105.
Description.—Small teeth with a short, slender crown; complete cutting edges; and a recurved mesial edge and straight to convex distal edge forming a distinct notch with a rounded distal heel. The root is thin with a deep transverse groove that penetrates a horizontal basal margin. Rhizoprionodon sp. from the Chucunaque Formation range from CH = 1.9–2.4mm and CW = 4.1–5.1mm.
Materials.—Fifty-five isolated teeth; indeterminate position: UF 275091, UF 281364–281268, and UF 281370.
Remarks.—Much confusion remains regarding the identification of Rhizoprionodon teeth, due to the closely aligned teeth of Sphyrna and, possibly synonymous, teeth of Scoliodon and Loxodon that were established by Springer (1964). Rhizoprionodon sp. differs from Sphyrna lewini in having a shorter crown, recurved mesial edge, and less pronounced root. Rhizoprionodon sp. differs in proportional size relative to Sphyrna,with Sphyrna having a greater crown height to width ratio (Purdy et al., 2001). Cappetta (1987) mentioned a marked sexual dimorphism in Rhizoprionodon, but it is possible that fossil specimens described may actually represent the morphologically similar Scoliodon and/or Loxodon. Consequently, identification of teeth from this genus should be treated with some degree of skepticism. Cappetta (1987) states that Rhizoprionodon teeth do not exceed CH = 4mm; however, Purdy et al. (2001) reported a range from CH = 3.2–5.2mm and CW = 4.3–5.7mm. Teethofthe GatunFormation (CH = 2.5– 3.3mm and CW = 3.9–5.6mm; Pimiento et al., 2013a) are more closely aligned with those of the Chucunaque Formation. Rhizoprionodon previously has been reported from the middle and late Miocene of France, Belgium, and Portugal (Cappetta, 1987). Carrillo-Briceño et al. (2015a) noted Rhizoprionodon as a small
531
component (~4%; N = 20) of the bathyal Piña Sandstone facies, but no occurrences in the neritic Rio Indio facies of the Chagres Formation. Extant individuals can be found worldwide in shallow, nearshore tropical and temperate waters (Compagno, 1984; Kent, 1994). Rhizoprionodon terraenovae occurs at depths ranging from the intertidal zone to 280m, but usually occur at depths less than 10m (Compagno, 1984; Compagno et al., 2005).
Family Sphyrnidae Gill, 1872 Genus Sphyrna Rafinesque, 1810
Type.—Squalus zygaena Linnaeus, 1758 (Cappetta, 2012).
Sphyrna lewini (Griffith and Smith, 1834) Figure 7.9–7.12
Holotype.—Originally described as Zygaena lewini by Griffith and Smith(1834inCuvier, Griffith, and Smith, 1834, p. 640, pl. 50). Holotype information is unknown, however the type locality is the south coast of New Holland (Australia) (Compagno, 1984).
Occurrence.—STRI 290109, STRI 290113, STRI 290125, and STRI 290145.
Description.—Small teeth with a stout to slender, distally inclined crown and prominent distal heel. Cutting edges are complete and lack serrations; the mesial edge is straight to slightly concave and the distal edge is straight and inclined forming a deep notch. The distal heel is rounded and has an unserrated cutting
edge.The root is thick with a deep nutrient groove that penetrates a horizontal basal margin. Sphyrna lewini from the Chucunaque Formation ranges from CH = 2.0–4.6mm and CW = 4.9–7.5mm.
Materials.—Thirteen isolated teeth; upper: UF 281176; indeterminate position: UF 275048, UF 275050, UF 275075, UF 275106, and UF 275153.
Remarks.—Sphyrna lewini differs from Rhizoprionodon in having a straighter mesial edge, taller crown, and thicker root. Sphyrna lewini specimens from the Chucunaque Formation are smaller than those recorded from the Gatun Formation (CH = 2.7–5.4mm and CW = 5.2–11.0mm; Pimiento et al., 2013a) and the Yorktown Formation (CH = 7.3–7.8mm and CW = 6.5–9.6mm; Purdy et al., 2001). However, it is possible that some of the larger teeth identified as Sphyrna zygaena actually represent S. lewini, which would result in a more comparable size range. Sphyrna lewini has also been reported from the late Miocene Chagres Formation of Panama (Carrillo-Briceño et al., 2015a) and the Miocene of Cuba (Iturralde-Vinent et al., 1996; MacPhee et al., 2003). Extant Sphyrna lewini have a circumglobal distribution in warm temperate and tropical seas, occurring over continental and insular shelves and adjacent deep water less than ~275m depth (Compagno, 1984; Compagno et al., 2005). Large schools of small individuals have been observed migrating poleward in the summer, however perma- nent resident populations also exist (Compagno, 1984).
Sphyrna mokarran (Ruppell, 1837) Figure 7.13–7.18
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