Perez et al.—Miocene sharks and rays from Lago Bayano, Panama
bottom waters at depths of 0–730m(McMillan et al., 2011), but most frequently occurs between 100 and 500m (Compagno, 1984, 2001; Compagno et al., 2005; Mundy, 2005). Alopias superciliosus is more tolerant of cold water, as low as 6°C, than most other sharks identified from Lago Bayano and has been observed occupying colder, deep water (200–550m and 6–11°C) during the day and shifting to warmer, mixed layers at night (50–130m and 15–26 °C; Smith et al., 2008).
Alopias cf. A. vulpinus (Bonnaterre, 1788) Figure 4.21–4.24
Holotype.—Originally described as Squalus vulpinus by Bon- naterre (1788, p. 9, pl. 85, fig. 349). According to Eschmeyer (1998), the holotype is unknown; however, the type locality is the Mediterranean Sea (Compagno, 2001, p. 86).
Occurrence.—STRI 290109 and YPA105.
Description.—Short, triangular teeth with a broad base and acutely pointed apex. The cutting edges are complete, but lack serrations. The mesial edge is straight and the distal edge is convex or vertical. The enameloid extends well onto the root on the labial face. Robust root usually lacking a nutrient groove, root lobes are rounded and elongate, basal margin is smoothly concave. Alopias cf. A. vulpinus from the Chucunaque Forma- tion range from CH = 1.2–7.1mm and CW = 4.5–8.3mm.
Materials.—Five isolated teeth; upper:UF 281321; indeterminate position: UF 275049 and UF 281320.
Remarks.—Kent (1994) identified two species of Alopias in the Chesapeake Bay region: Alopias superciliosus and Alopias latidens. However, Purdy et al. (2001) questioned the validity of Alopias latidens and, consequently, identified Alopias superciliosus and Alopias vulpinus as the only two thresher sharks that occur in the Lee Creek Mine. Descriptions of both A. latidens (Kent, 1994) and A. vulpinus (Purdy et al., 2001) align well with what is observed for Alopias cf. A. vulpinus from the Chucunaque Formation. Anterolateral teeth of A. vulpinus from the Pungo River Formation range from CH = 8.0–15.0mm and were estimated to have correlated to a TL = 4.5–6m (Purdy et al., 2001), which indicates that individuals from the Chucunaque Formation were smaller in size. Extant individuals of A. vulpinus have a cosmopolitan distribution in temperate and tropical seas, occurring in coastal and oceanic waters at depths from 0–550m (Compagno, 1984; Cox and Francis, 1997); but most frequently are found near land at depths of 1–366m (Compagno et al., 2005; Mundy, 2005). Young individuals are often found close inshore and in shallow bays (Compagno et al., 1989; Compagno et al., 2005). Alopias vulpinus is frequently encountered in temperate waters and more common in coastal environments than any of the other thresher sharks (Smith et al., 2008).
Order Carcharhiniformes Campagno, 1973 Family Triakidae Gray, 1851
Genus Iago Compagno and Springer, 1971
521 Type.—Eugaleus omanensis Norman, 1939 (Cappetta, 2012).
cf. Iago sp. Figure 3.3–3.6
Occurrence.—STRI 290109 and YPA105.
Description.—Extremely small teeth with a short crown and root. The crown is distally arched with complete cutting edges. The mesial edge is slightly sigmoid, with a concave base and straight or concave apex; while the distal edge is convex or straight. There is a prominent rounded distal heel that forms a distinct notch. Lingual face is convex and the labial face is flat with weak folds at the crown base. The crown-root contact on the lingual face shows two distinct depressions on the mesial and distal edges where the crown thins out. On the labial face this contact is sharp, forming a distinct ridge. The root is high up on the lingual face with an observable lingual protuberance and distinct transverse furrow that penetrates the labial face. From the Chucunaque Formation cf. Iago sp. range from CH = 0.61–0.86mm and CW = 1.01–1.67mm.
Materials.—Thirty-six isolated teeth; lateroposterior: UF 281374, UF 281376, UF 281379; indeterminate position: UF 281373; UF 281375, UF 281377, UF 281378, and UF 281380–83.
Remarks.—These are among the smallest shark teeth found in Lago Bayano and are only found through screenwashing efforts. Teeth of cf. Iago sp. are about half the size of those attributed to Physogaleus sp. There are distinct similarities to Iago oamanensis imaged in Herman et al. (1988), particularly the complete cutting edges with a rounded distal heel that forms an acute notch with the principle
cusp.Lateral teeth of some species of Triakis,such as T. semifasciata and T. acutipinna, have a similar morphology (Herman et al., 1988); however, anterior teeth bear lateral cusplets that were not observed in any of the recovered specimens. Neither Iago nor Triakis have previously been reported from the fossil record of Panama. There are two extant species of Iago, I. garricki and I. omanensis, both of which have a bathydemersal habit. Iago garricki is a tropical species occurring in the Pacific Ocean on upper continental and insular slopes between 250 and 475m. Iago omanensis occurs in the Indian Ocean and prefers warm, poorly oxygenated water at depths of less than 110 to over 1000m (Compagno et al., 2005).
Genus Mustelus Linck, 1790 Type.—Squalus mustelus Linnaeus, 1758 (Cappetta, 2012).
Mustelus sp. Figure 3.7–3.13
Occurrence.—STRI 290109, STRI 290113, and YPA105.
Description.—The occlusal surface is smooth and has an elongate, roughly elliptical outline in apical view. The labial edge forms a prominent ridge at the crown-root margin and has a convex edge with folds that may be weak or strongly pronounced. The lingual face has a large central uvula with
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