The Sevengill shark is a large (to 3m, possibly reaching 4) shark which according to Compagno (1984 & 2005) inhabits shallow (1-135m), temperate coastal continental waters. They are found in isolated regions worldwide; however, they
are no longer present in the Western North Atlantic. Within their environment they are top predators feeding on other sharks, rays, teleosts, marine mammals and carrion. These generally benthic sharks may feed through-out the water column.
In the extant taxon, Notorhynchus cepedianus (PERON 1807), the dentition displays dignathic heterodonty and is cutting-grasping in function, Unlike the lamniforms and carcharhinids, it is the upper teeth that grasp and the lowers that cut (or more descriptively -- saw). The upper quadrates each have seven large mesially-positioned teeth (6 if the parasymphyseal is deemed such) followed by numerous (10 or so) tiny distally-postioned teeth. The lower quadrates share a symphyseal, have six mesio-laterals and less numerous posterio-laterals (7 or so).
The broad rectilinear root and multiple conules give the family's labio-lingually compressed lower teeth their aesthetically pleasing and broadly-desired appearance. The large first conule (acrocone) is followed by 6-7 conules that decline is size distally; in lower teeth, the mesial base of the acrocone is usually strongly serrate. The relative height and orientation of the acrocone to the conules reflects sexual dimorphisim (taller and more erect in the males). The upper teeth have an acrone but may lack a conule in the first couple positions; remaining mesio-laterals have a one to three reduced conules. The posterior teeth are very small, molarform1 and somewhat irregular in shape. Due to their size and total lack of conules, they are seldom found and when found difficult to recognize as to genus/species.
Known from isolated teeth only, Cappetta (1987:48) similarly defines the genus and noted that the conule count may vary between 4-7 and that these teeth are less mesio-distally elongated relative to Hexanchus. He included three representative species:
N. aptiensis (PICTET 1865) Upper Aptian (Lower Cretaceous) Southern France.
N. primigenius (AGASSIZ 1843b) Oligo-Miocene of NA, Europe & Australia
N. serratissimus (AGASSIZ 1843b) Ypresian, England
In commenting on symphyseals, Kent (1994:17-20) noted that while the medial conule is erect in Hexanchus, it is often lacking in Notorynchus and all conules may flop to either side (speculation, female, see Fig. ). He went on to include two species as present in the Chesapeake region:
N. serratissimus Aquia (Paleocene) & Nanjemoy (Ypresian) Formations
N. primigenius Old Church (Oligocene), Calvert, Choptank and Eastover (Miocene) Formations.
Purdy et al (2001 83-84) reported Notorynchus from the Pungo River (unit 1-5, Miocene) and Yorktown (units 1-2, Pliocene) Formations of Lee Creek, NC. They discussed the similarities of both tooth and dentition-designs of the extant taxon with these fossil specimens -- concluding primigenius to be a junior synonym of cepedianus.
A California Perspective
Unlike Lee Creek where Notorynchus teeth are common and Hexanchus scarce, in the Round Mountain Silt at Sharktooth Hill, the former is rare and the latter relatively common. This specimen likely represents N. cepedianus.
||Asked about the usage of the term molarform, Bill Heim (pers. com 2008) responded, "I am going to have to stick with molarform for the posteriors. They are nothing like the Echinorhinus [priscus] tooth you directed me to. The have no cusps / conules / cutting edge at all. Instead of a cusp / cutting edge, they have a thickened rounded ridge that runs along the top of the tooth. Look more like the posterior teeth of S. tiburo. If you were to find one in the mine, you wouldn’t have a clue as to what it was. Probably think it was a worn something."|
Cappetta, H., 1987. Chondrichthyes II: Mesozoic and Cenozoic Elasmobranchii. Handbook of Paleoichthyology, 3B. Gustav Fischer Verlag, Stuttgart and New York, 193 pp.
Kent, B. 1994. Fossil Sharks of the Chesapeake Region. Egan Rees & Boyer, Maryland, 146 pp.
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., 1979. Additions to the fish fauna of the English Palaeogene. 3. A review of the Hexanchid sharks with a description of four new species. Tertiary Research, 2 (3) pp 111-129.
Welton, B. J. and R. F. Farish 1993. The Collector's Guide to Fossil Sharks and Rays from the Cretaceous of Texas. Before Time, Texas. 204 pp.
Other elasmo.com references
by Bill Heim