Compagno (1999) recognized seven extant species of sharpnose sharks. These are generally inshore sharks but, depending on species, may be found in continental & insular shelf waters to 500m. The genus is represented circum-globally in tropical, subtropical and, in the case of Rhizoprionodon terraenovae (RICHARDSON, 1836), warm temperate waters. The small sharks of this genus (to 1.7m, usually less than 1 m) feed primarily on bony fish, but also eat a variety of invertebrates.
When attempting to compare fossil Rhizoprionodon teeth with other described species, it is important to keep in mind the distribution of their living counterparts. Three species are present
in waters which include the Eastern South Atlantic, Indian Ocean and Western South Pacific --
R. acutus (RUPPELL, 1837),
R. oligolinx SPRINGER, 1964 and
R. taylori (OGILBY, 1915). The Western Atlantic is home to three other species,
R. terraenovae (Caribbean to Nova Scotia) and in the Caribbean and South Atlantic -
R. lalandii (VALENCIENNES, 1839) and
R. porosus (POEY, 1861). A single species,
R. longurio (JORDAN & GILBERT, 1882), is present in the Eastern Pacific.
Because of the similarity of teeth amongst the living species, ascribing similar fossil teeth in one area (i.e. R. fischeuri (JOLEAUD 1912) from the Miocene of Europe to teeth from the Western Atlantic) to those in another should be done with care.
The teeth of this genus have a distally directed cusp with a complete cutting edge and a distal shoulder or heel. In most species, this shoulder is rounded and smooth, however, the heel of R. acutus is angular and weakly serrate. The cusps of male teeth tend to be narrower and thicker than those of the female. A diagnostic feature of Rhizoprionodon teeth is a recurvature of the upper cusp. When viewed labially (or lingually) the mesial edge of the upper cusp is straight to concave and the distal edge, convex. The teeth are small (usually less than 4.0 mm in height) and have a root with a rectilinear basal margin and distinct nutrient groove.
Cappetta (1987: 126-27) discussed two fossils species, Rhizoprionodon ganntourensis (ARAMBOURG 1952) from the Eocene of North Africa & Europe and R. fischeuri (JOLEAUD 1912) from the Middle & Upper Miocene of Europe. In North America reports include:
Case (1980: 91) reported a single symphyseal-type tooth which was ascribed to ?Rhizoprionodon sp.
Kent (1994: 87) included R. fischeuri in the Miocene fauna of the Chesapeake Region (Western North Atlantic) and (1999) did not recognize the genus in the Nanjemoy Fm. (Ypresian).
Müller (1999: 53-54) included R. fischeuri from the Oligocene Old Church Fm (VA) and Trent Marls (NC); R. aff terranovae from the Oligocene Belgrade and Pliocene Yorktown Fms (NC); and Rhizorionodon sp for a single tooth from the Piney Pt Fm (Lutetian VA).
Case & Borodin (2000) included in the Castle Hayne fauna (Lutetian) as Physogaleus sp, teeth of the Rhizoprionodon-design (Plate figures:48, 49 & 51). They also erected as Paragaleus duplinensis another tooth-design (fig 52 & 53) which reflects elements of Physogaleus and Rhizoprionodon. The teeth of this fauna need serious study inorder to determine the actual genera present.
Purdy et al (2001: 155) prefered to refer to their Lee Creek material (Pungo RiverFM) as ?Rhizoprionodon sp based on the general lack of distinguishing characteristics of isolated teeth (when comparred with other similar taxa).
The Ypresian sediments of the Nanjemoy (Potapaco Beds "A" and "B") produce teeth of the Rhizoprionodon design (Fig. , & ). In addition, to these teeth, other teeth are found which are reminiscent of Rhizoprionodon, but have an angular heel. Lutetian sediments of the Castle Hayne Formation also include Rhizoprionodon-type teeth as depicted in figures and .
The Miocene sediments of the Pungo River (North Carolina) produce R. fischeuri-like teeth. In addition, the basal Yorktown sediments yield teeth which compare very well with the teeth from the extant species R. acutus.
Cappetta, H., 1987. Chondrichthyes II: Mesozoic and Cenozoic Elasmobranchii. Handbook of Paleoichthyology, 3B. Gustav Fischer Verlag, Stuttgart and New York, 193 pp.
Case.G., 1980. A Selachian Fauna from the Trent Formation, Lower Miocene of Eastern North Carolina In: Palaeontographica, 171:75-103.
Case.G. & Borodin, P., 2000. A Middle Eocene Selachin Fauna from the Castle Hayne Limestone Formation of Duplin County, NC, Munchner Geowiss. Abh.. 39:17-32.
Compagno, L.J. 1999. Checklist of living elasmobranchs. In Sharks, skates, and Rays - The Biology of Elasmobranch Fishes. Hamlett, W. C. ed. John Hopkins University Press, Baltimore MD, USA. pp 471-498.
Kent, B. 1994. Fossil Sharks of the Chesapeake Region. Egan Rees & Boyer, Maryland, 146 pp.
Kent, B. 1999. Sharks from the Fisher/Sullivan Site. In: Weems, R. & Grimsley, G., Early Eocene Vertebrates and Plants from the Fisher/Sullivan Site (Nanjemoy Formation) Stafford County, Virginia. Virginia Division of Mineral Resources, Pub 152: 11-37.
Müller, A. 1999. Ichthyofaunen aus dem atlantischen Tertiär der USA. Leipziger Geowissenschafteb, Leipzig, 9/10: 1-360.
Purdy, R., Schneider, V., Appelgate, S., McLellan, J., Meyer, R. & Slaughter, R., 2001. The Neogene Sharks, Rays, and Bony Fishes from Lee Creek Mine, Aurora, North Carolina. In: Geology and Paleontology of the Lee Creek Mine, North Carolina, III. C. E. Ray & D. J. Bohaska eds. Smithsonian Contributions to Paleobiology, No 90. Smithsonian Institution Press, Washington D.C. pp. 71-202.
Ward, D. J. and Wiest, R.L., 1990. A checklist of Paleocene and Eocene sharks and rays (Chondrichthyes) from the Pamunkey Group, Maryland and Virginia, USA. Tertiary Res., 12(2) p 81-88.