Perez et al.—Miocene sharks and rays from Lago Bayano, Panama Occurrence.—STRI 290145 and STRI 300032.
Description.—Flat, wide teeth with a low crown, a smooth occlusal surface, and often trapezoidal outline. Labial edge is straight or convex; lingual edge straight or concave; extremities of tooth plates are oriented distally. Root is short and poly- aulacorhizid with oblique, parallel root lobes. In occlusal view, the root extends beyond the crown on the labial edge.
Materials.—Six isolated tooth fragments; indeterminate position: UF 281225–26.
Remarks.—Teeth of Aetobatus sp. can be distinguished from Rhinoptera by their lower crown, rounded and distally oriented extremities, and oblique root lobes that extend beyond the crown (Laurito and Valerio, 2008). Aetobatus cf. A. narinari was repor- ted from the Gatun Formation and was fairly common (N = 22); however, only one specimen was a complete tooth with the following dimensions: CW = 66.0mm, CL = 8.0mm, and CH = 4.5mm(Pimiento et al., 2013a). In contrast, Aetobatus sp. from the Chucunaque Formation is fairly uncommon (N = 6) and no complete specimens were recovered for an accurate size compar- ison. Aetobatus and Rhinoptera,aswellas Myliobatis and Aeto- mylaeus, have dental plates that are formed by numerous interlocking teeth that comprise a large crushing surface primarily used to feed onmollusks and decapods (Compagno, 1997).Extant Aetobatus narinari has a cosmopolitan distribution in subtropical and tropical seas, commonly occurring in shallow waters between 1 and 60m depth (Mundy, 2005).
Family Rhinopteridae Jordan and Evermann, 1896 Genus Rhinoptera Kuhl in Cuvier, 1829
Type.—Myliobatis marginata Geoffroy Saint-Hilaire, 1809 (Cappetta, 2012).
Rhinoptera sp. Figure 10.4–10.15
Occurrence.—STRI 290109, STRI 290116, STRI 300029, STRI 300032, and STRI 430011.
Description.—Thick, elongate teeth with a smooth occlusal sur- face and hexagonal outline; fragmented tooth plates often have a rectangular outline. In cross-section, the enamel is comprised of vertical prisms that radiate outward from the pulp cavity, indi- cating extensional growth. Labial face bears a transverse plat- form, which interlocks with the lingual visor of the proceeding tooth (Pimiento et al., 2013a). Symphyseal teeth interlock with smaller lateral teeth via their angular extremities (Cappetta, 1987). In lateral teeth, the crown is thicker towards the mesial edge than the distal edge. Root is polyaulacorhizid with numerous lobes, fewer lobes in the smaller lateral teeth; the root is short relative to the crown. Rhinoptera sp. from the Chucunaque Formation has a CH = 1.9–4.3mm, CW = 3.1–5.7mm, and CL = 6.4–16.4mm.
Materials.—Thirty-eight isolated teeth; 10 complete and 18 fragments; symphyseal: 281307; lateral: UF 281227,UF 281304,
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Figure 10. Batoid II: Aetobatus and Rhinoptera images from the Chucunaque Formation. (1–3) Aetobatus sp., UF 281226, distal tooth fragment in occlusal, basal, and lateral view, respectively; (4–15) Rhinoptera sp.: (4–7) UF 281307, symphyseal (i.e., medial) tooth in occlusal, basal, lingual, and lateral view, respectively; (8) UF 281309, cross-section in lateral view; (9–11) UF 281308, lateral (i.e., intermediate) tooth in occlusal, basal, and lingual view, respectively; (12–15) UF 281304, lateral (i.e., distal) tooth in occlusal, basal, lingual, and labial view, respectively (scale bars = 5 mm). Photo credit: S. Moran.
UF 281308, UF 281311, UF 281313; indeterminate position: UF 281302-281303, UF 281305–06, and UF 281309-281311.
Remarks.—Rhinoptera can be distinguished from Aetobatus by its high crown and hexagonal outline with angular extremities. Rhinoptera is also often confused with Myliobatis; however, Rhinoptera differs in having a higher crown, a more angular occlusal surface, and a thicker lingual cingulum (Laurito and Valerio, 2008). Myliobatis was not observed in the Chucunaque Formation, but has been reported from the Gatun Formation, along with Rhinoptera cf. R. steindachneri (Pimiento et al., 2013a). The small, yet significant, relative abundance of Rhinoptera in the Gatun Formation (~4%) is comparable to that seen in the Chucunaque Formation (2.7%; Fig. 12). The size range of Rhinoptera teeth from the Gatun Formation (CH = 3.0–5.0mm, CW = 3.0–26.0mm, and CL = 4.0–5.0mm) is fairly close to that observed in Bayano. The significantly larger range in CW can likely be explained by the occurrence of a large symphyseal tooth in the Gatun Formation. Rhinoptera steindachneri occurs in tropical waters in the eastern Pacific, usually between 0 and 30m depth (Humann and Deloach, 1993).
Family Mobulidae Gill, 1893 Genus Mobula Rafinesque, 1810
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