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Journal of Paleontology 91(3):512–547
Mobula pectinata. Adnet et al. (2012) placed M. tarapacana in a distinct group within the mobulids characterized by having a cobblestone tooth plate. Extant individuals have a circumglobal distribution in temperate and tropical environments (Notarbartolo Di Sciara, 1987; Clark et al., 2006b). Mobula tarapacana is predominantly oceanic, but also occurs in coastal waters, inhabit- ing depths of 0–30m (Feitoza et al., 2003).
Mobula spp. Figure 11.26–11.50
Occurrence.—STRI 290109, STRI 290113, STRI 290116, and YPA105.
Description.—Numerous tooth forms with varying degrees of ornamentation were observed; however, they can be broadly placed into three morphotypes. Type I teeth lack ornamentation altogether (Fig. 11.26–11.31), and may be irregularly cuspidate (Fig. 11.26), bicuspidate (Fig. 11.31), or have a single cusp (Fig. 28). The crowns of Type I teeth are broad apically and slender basally, with enamel that extends well onto the root on the lingual face and forms a distinct ridge at the crown-root contact on the labial face. The root may be holaulochorizid or polyaulochorizid with slender, divergent root lobes. Many of these characters are similar to extant female Mobula tarapacana as well as the extinct species Mobula loupianensis, which is not unexpected given that Cappetta (1970) noted similarities between the two in his original description of M. loupianensis. UF 281287 has a CH = 0.91mm, CW = 1.06mm, and CL = 1.59mm (Fig. 11.31). Type II teeth have a prominent central cusp and may have
two or more minor lateral cusplets on the distal and mesial edges (Fig. 11.32–11.45). In apical view, the occlusal surface is smooth, but bears deep troughs and complimentary ridges that extend onto the labial edge. The root is low and narrow relative to the crown and is divided into two or three lobes; in UF 281251 and UF 281490 (Fig. 11.36, 11.43) the two lobes are weakly incised, beginning to form two additional lobes. This multicuspidate form strongly resembles extant males of the species Mobula hypostoma, but also bears similarities with extant males of Mobula rochebrunei and the extinct species Mobula loupianensis. UF 281251 has a CH = 0.71mm, CW = 0.92mm, and a CL = 2.09mm (Fig. 11.36–11.38). Type III teeth are elongate with a nearly hexagonal outline;
the crown is shallow and inclined with a concave occlusal surface bearing a granular ornament (Fig. 11.46–11.50). There is a transverse crest that follows the contour of the labial edge; the labial edge is slightly convex; and the lingual edge is straight to slightly concave. The mesial and distal edges may be angular or subrounded, likely due to positional variability within the dental plate (Adnet et al., 2012). The root is high relative to the crown, and may be holaulocorhizid or polyaulacorhizid. In UF 281299, the crown is short and subhexagonal, bearing a transverse crest that follows the contour of the labial edge. The labial side of the crest is coarsely ornamented; the lingual side has a fine ornamentation that fades out distally (Fig. 11.49, 11.50; CH = 0.17mm, CW = 1.51mm, and CL = 0.82 mm). The largest specimen, UF 281255 (Fig. 11.46–11.48), has a CW = 3.48mm and CL = 1.86mm.
Materials.—One hundred forty; Type I (N = 8): UF 281268, UF 281278–81, UF 281287–88, UF 281496; Type II (N = 60): UF 281239, UF 281241, UF 281243, UF 281246, UF 281248– 49, UF 281251, UF 281253–54, UF 281257–58, UF 281261– 63, UF 281265–67, UF 281273, UF 281282, UF 281286, UF 281290, UF 281296, UF 281298–99, UF 281490–91; Type III (N = 70): UF 281240, UF 281244–45, UF 281247, UF 281250, UF 281252, UF 281255, UF 281259–60, UF 281264, UF 281269, UF 281274–75, UF 281277, UF 281297, UF 281486, UF 281489, UF 281492–95, UF 281498; indeterminate fragments (N = 2): UF 281300–01.
Remarks.—Notarbartolo Di Sciara (1987) noted that hetero- donty is one of the most salient mobulid characteristics and suggested that tooth morphology as a systematic tool may be problematic. Adnet et al. (2012) provided a comprehensive overview of the evolutionary history of mobulid rays with a particular focus on dental characters and the evolution of planktivory. The distinction between different species, and especially between different genders, is largely based on crown ornamentation. However, additional work must still be done to better understand the robustness of crown ornamentation as a phylogenetic tool, especially in consideration of other Miocene-aged extinct species such Mobula loupianensis, Mobula pectinata, Mobula fragilis, and Plinthicus. Cappetta (2012) attributed the reduction in tooth size and crown ornamentation in the genus Burnhamia to a change in diet, which may indicate a greater relationship between ornamenta- tion and environment than with evolutionary history. The tooth morphology of Type III teeth definitely resembles that of Burnhamia, which is considered a stem mobulid by Cappetta (1987, 2012). Burnhamia is an extinct genus that has been reported from the late Paleocene through the Eocene, and was placed in the family Mobulidae due to its reduced tooth size relative to rhinopterids (Cappetta, 2012). Given that sexual dimorphism is an extremely marked
character in the genus Mobula (Notarbartolo Di Sciara, 1987; Adnet et al., 2012; Cappetta, 2012), it seems likely that Type III teeth are female counterparts to the male Type II morphotype. The more cuspidate crowns of males compared to females likely reflect different feeding mechanisms and possibly different prey items, which would aid in reducing competition between genders. Adnet et al. (2012) places Mobula hypostoma in a group of mobulids characterized by having comb-like teeth, which are similar to the Type II morphotype described herein. Male teeth are imbricated with their cusps oriented lingually (Radcliffe, 1916; Notarbartolo Di Sciara, 1987), which may aid in grasping small prey and directing it inward. Mobula hypostoma feed primarily on zooplankton, but will also eat small pelagic crustaceans and ray-finned fishes (McEachran and Carvalho, 2002). Mobula hypostoma has been identified from the Gatun Formation of Panama (Pimiento et al., 2013a) and the late Miocene–Pliocene of Costa Rica (Laurito, 1999); however, Laurito (1999) only identified male M. hypostoma teeth. Extant individuals occur in tropical to subtropical waters in the Western Atlantic, and often have a coastal preference, but may occur in oceanic waters as well (Notarbartolo Di Sciara, 1987; McEachran and Carvalho, 2002; Bizzarro et al., 2009). Mobulid rays are placed in the aquilopelagic ecomorphotype described
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