Lamniform and Carcharhiniform Sharks from the Pungo River and Yorktown Formations (Miocene–Pliocene) of the Submerged Continental Shelf, Onslow Bay, North Carolina, USA
The submerged continental shelf of Onslow Bay, North Carolina, preserves hardbottom limestone scarps with underlying clays as small isolated exposures in progressively deeper water seaward from the modern-day shoreline. These scarps formed as a result of wave- and current-driven erosion, transport, and redeposition of bottom sediments due to glacioeustactic sea level cyclicity and the migration of the ancestral shoreline since the Pliocene. Fossiliferous lag deposits containing an abundance of lamniform and carcharhiniform teeth, including those belonging to megatoothed sharks, occur adjacent to these scarps. These specimens include teeth from: Alopias grandis, Carcharhinus falciformis, Carcharhinus priscus, Carcharias cf. C. taurus, Carcharodon carcharias, Carcharodon hastalis, Galeocerdo aduncus, Galeocerdo cuvier, Hemipristis serra, Isurus oxyrinchus, Negaprion brevirostris, Otodus chubutensis, Otodus megalodon, Parotodus benedinii, Physogaleus contortus, and Rhizoprionodon sp. Comparison of biostratigraphically significant lamniform and carcharhiniform taxa from the submerged shelf with those from land-based assemblages along the Atlantic Coastal Plain of the USA indicates that the shallower shelf (≈25 m deep) exposes the Miocene Pungo River Formation and intermediate and deeper shelf (≈30–35 m deep) expose the Pliocene Yorktown Formation. Many of the Onslow Bay lamniforms and carcharhiniforms also occur in Miocene and Pliocene shallow marine assemblages around the world and reinforce the migratory abilities of these chondrichthyans in the late Cenozoic and the utility of lamniform and carcharhiniform teeth in biostratigraphic and chronostratigraphic analyses.
Onslow Bay Study Area. (A) Inset map of the Atlantic Coastal Plain of the United States showing the Onslow Bay study region (star) and maximum extent of marine inundation during the Middle Miocene ≈18 Myr ago (red line) and sea level lowstand during the Last Glacial Maximum ≈18 Kyr ago (black line). (B) Map of the Cape Fear Region of southwestern Onslow Bay showing bathymetric contours and the seismic stratigraphic sediment divisions beneath Onslow Bay modified from Snyder et al. (1982) and Snyder et al. (1988, 1993). Letters a, b, and c show the locations of our shallower (a), intermediate (b), and deeper (c) fossiliferous shelf localities discussed in this study.
Generalized stratigraphic column for the PCS Phosphate Mine (modified from Ward, 2007), and shallower, intermediate, and deeper Onslow Bay study localities described in this report in relation to the Miocene–Holocene glacioeustactic sea level cyclicity curve of Riggs et al. (1985). Formation abbreviations: FB = Flanner Beach; JC = James City; CR = Croatan; YT = Yorktown; EO = Eastover Formation; PR = Pungo River. Note the absence of the Eastover Formation at the PCS Phosphate Mine and extensive amount of erosion in Onslow Bay.
Geology of the three submerged localities. (A) Cross-sectional diagram of the Pungo River Formation as exposed at the shallower shelf locality. (B) Underwater image of large, abundant cobble clasts, designated by arrows, exposed on the seafloor at the shallower shelf locality. (C) Cross-sectional diagram of the Yorktown Formation as exposed at the intermediate and deeper shelf localities. (D) Underwater image of Yorktown Formation clay with bioerosion indicated by arrows. (E) Underwater image of large, encrusted Otodus megalodon tooth from the shallower shelf locality (Image courtesy of Capt. Z. DeWitt).
Lamniform teeth in the Onslow Bay assemblage from the shallower, intermediate, and deeper shelf localities. (A, B) Carcharias cf. C. taurus (ANSP 24151); (C–F) Isurus oxyrinchus (ANSP 24135–24136); (G–J) Otodus chubutensis (ANSP 24127–24128); (K, L) Otodus megalodon (ANSP 24110); (M, N) Carcharodon carcharias (ANSP 24129); (O–R) Carcharodon hastalis (ANSP 24132–24133); (S, T) Alopias grandis (ANSP 24138); (U, V) Parotodus benedinii (ANSP 24139). Orientations: Lingual = A, C, E, G, I, K, M, O, Q, S, U. Labial = B, D, F, H, J, L, N, P, R, T, V. Scale bars: A–J, M–T = 2 cm and K–L, U–V = 5 cm.
Carcharhiniform teeth in the Onslow Bay assemblage from the shallower, intermediate, and deeper shelf localities. (A–D) Hemipristis serra (ANSP 24140–24141); (E–H) Carcharhinus priscus (ANSP 24147–24148); (I, J) Carcharhinus falciformis (ANSP 24163); (K, L) Negaprion brevirostris (ANSP 24150); (M, N) Physogaleus contortus (ANSP 24144); (O, P) Galeocerdo aduncus (ANSP 24145); (Q, R) Galeocerdo cuvier (ANSP 24146); (S, T) Rhizoprionodon sp. (ANSP 24149). Orientations: Lingual = A, C, E, G, I, K, M, O, Q, S. Labial = B, D, F, H, J, L, N, P, R, T. Scale bars: A–D, Q–R = 2 cm and E–P, S–T = 1 cm.
Additional, unique fossil remains from the Onslow Bay assemblage recovered from the shallower, intermediate, and deeper shelf localities. (A) Large tooth of Otodus megalodon likely from an individual with a total length >12 m based on a crown height measurement of 14 cm (In the private collection of B. Karasik). (B) Tooth of O. megalodon displaying angular cusp break that may have been caused by feeding damage as described by Becker et al. (2000) and Becker and Chamberlain (2012) (In the private collection of B. Major). Evidence of bioerosion from endolithic bivalves (e.g., Lithophaga sp.), indicated by arrows, in vertebrate fossils including (C) cetacean bone and (D) O. megalodon tooth. (E) Cetacean phalange with traces of feeding damage, indicated by arrows, from a large chondrichthyan (e.g., O. megalodon) (In the private collection of Capt. S. Jenkins). Pleistocene megafaunal remains recovered from the shallower shelf locality: (F) mastodon tooth and (G) mammoth tooth (Both teeth in the private collection of Capt. S. Jenkins).
Contributor Notes
Associate Editor: M. P. Davis.