Guitarfish are benthic batoids inhabiting warm, shallow waters, of the continental shelf. The genus Rhinobatos is represented by 26 living species, only two of which can be found off the East Coast of the United States (from North Carolina south) - R. percellens (WALBAUM 1792) and R. lentiginosus GARMAN 1880. Two other species inhabit California waters - R. productus GIRARD 1855 and R. glaucostigma JORDAN & GILBERT 1883. The dentition is of a crushing design, incorporating hundreds of juxtaposed small teeth.

Dating to the Lower Jurassic, guitarfish are a relatively conservative chondrichthyan family. Unlike so many batoids, the rhinobatid genera are well represented by fossil skeletons and evolutionary changes have been noted in body design, but not the teeth. Cappetta (1987) included nine genera as being represented in the fossil record, but only one, Rhinobatos, as represented in North American deposits - R. casieri HERMAN in CAPPETTA & CASE 1975 (Campanian, New Jersey) and R. incertus CAPPETTA 1973 (Turonian, South Dakota). Welton and Farish (1993) included R. casieri (Campanian) and R. incertus (Turonian-Coniacian) in the Cretaceous of Texas.

The teeth of the species are very small and usually require mesh sizes of 1.2 mm or less to be recovered. The teeth appear to have a rather globular crown, but magnification reveals a transverse ridge and strong lingual & relatively strong lateral, uvulae. The roots extend beyond the lingual face of the crown, and when viewed basally, narrow lingually and have a strong nutrient groove. The lateral faces of the root are strongly notched and usually reveal the associated margino-lingual foramina.

The teeth of Rhinobatos casieri have a high crown and relatively strong transverse ridge. The lingual uvula is strong and the lateral uvulae less extended. The tooth's enameloid is smooth and the labial visor is convex in profile. Anterior to the transverse ridge, there are weak depressions on either side of the crown. The central pore is large and the margino-lingual foramina, usually distinct.

Fig. 1 - Rhinobatos cf casieri 98-JAB-BB-119 Big Brook (Campanian), New Jersey hgt = 1.5, wid = 1.8, dep = 1.7 mm

Cappetta (1987) listed two Eocene species from Western Europe, R. bruxelliensis (JAEKEL 1894) and R. steurbauti CAPPETTA & NOLF 1981 but none from North America. Insufficient information has been located to suggest a positive identification for the below Nanjemoy specimens.

Fig. 2 - Rhinobatos sp 97-JAB-MC-241-S01 Potapaco Bed "A" (Ypresian), Virginia hgt = 1.0, wid = 1.8, dep = 1.5 mm

Fig. 3 - Rhinobatos sp, unworn crown Potapaco Bed "B" (Ypresian), Virginia reconstructed from 2 specimens hgt = estim 1.9, wid = 1.9, dep = 2.0 mm From collections of Folmer & Bourdon

Additional Reference

Extant Guitarfish -- Rhinobatos sp