Fossil Sea Turtles from the Early Pliocene Bone Valley Formation, Central Florida

Abstract

Four genera of cheloniid (Caretta, Chelonia, Eretmochelys, Lepidochelys) and one genus of dermochelyid (Psephophorus) sea turtles are recorded from the Bone Valley Formation of central Florida. The fossils derive from phosphate deposits of early Pliocene (late Hemphillian) age, 4.5-5 Ma. Although similar in age to fossils from the Yorktown Formation (Lee Creek Mine) in North Carolina, the Bone Valley sea turtle fauna appears to lack two genera found at Lee Creek (Syllomus, Procolpochelys) and contains one genus that is not found at Lee Creek (Eretmochelys). The Caretta from the two areas may not be conspecific. The fossil Chelonia, Eretmochelys, and Lepidochelys cannot be distinguished confidently from modern species, but conversely only the Lepidochelys appears obviously related to a particular modern species, L. kempi. This paper provides the first report of Eretmochelys in Pliocene deposits and the first association of Psephophorus with all living cheloniid genera except the Australian Natator. We suggest that shallow seas in the Bone Valley region provided rich feeding habitat for sea turtles in the early Pliocene in the same way that shallow water habitats in Florida and the Bahamas support a similar assemblage today. The Bone Valley phosphate mining region of central Florida long has been known as a rich source of terrestrial and marine vertebrate fossils (Sellards, 1916; Allen, 1921; Simpson, 1930; Kellogg, 1944; Brodkorb, 1955). Phosphatic sediments of the Bone Valley Formation in this region have produced a sequence of vertebrate faunas dating from the middle Miocene (about 16 Ma) to the early Pliocene (4.5 Ma) (Webb and Hulbert, 1986). The best known Bone Valley fauna is early Pliocene in age and has been referred to the late Hemphillian North American Land Mammal Age (NALMA; Berta and Morgan, 1985; Webb and Hulbert, 1986; Tedford et al., 1987). Following Webb and Hulbert (1986), we use the term Palmetto Fauna to distinguish the late Hemphillian vertebrate assemblage from older faunas present in the Bone Valley region. The Palmetto Fauna contains a fossil assemblage representing marine, estuarine, freshwater, and terrestrial components, and appears to have accumulated at a time when sea levels were about 50 m higher than present (Webb and Tessman, 1968; MacFadden and Webb, 1982). The marine and estuarine components consist of sharks, rays, bony fish, sea turtles, pelagic birds, and many marine mammals, including a walrus, three species of seals, a sea otter, a sea cow, and numerous cetaceans (Berta and Morgan, 1985). The presence of sea turtles in late Hemphillian age deposits in the Bone Valley region was noted briefly by Berta and M rgan (1985) and Dodd (1990), but these fossils have not been previously described. Tertiary sea turtle fossils have been described from a number of localities on the Atlantic Coastal Plain, including the Paleocene Hornerstown Sand and Vincetown Formation and Eocene Manasquan Formation of New Jersey (Weems, 1988), the Paleocene Brightseat and Aquia Formations of Maryland and Virginia (Weems, 1988), the Oligocene Ashley Formation of South Carolina (Hay, 1923), the Miocene Kirkwood Formation of New Jersey (Zangerl and Turnbull, 1955; Weems, 1974), the Miocene Calvert Formation of Maryland and Virginia (Weems, 1974, 1980), and the Pliocene Yorktown Formation in North Carolina (Zug, in press). The very few published records of Tertiary sea turtles from the Gulf Coastal Plain include a questionable Eocene dermochelyid from Alabama (Thurmond and Jones, 1981) and a middle Eocene cheloniid from Florida (P. Meylan, 1984). There also are some unreported cheloniid fossils from Florida, mostly consisting of shell fragments, from the middle Eocene Avon Park Limestone and Inglis Formation and the Oligocene Suwannee Limestone (G. Morgan, unpubl. obs.). A few Florida Pleistocene fragments belonging to modern genera (Chelonia, Caretta) were mentioned by Hay (1916, 1917), but no comprehensive summary or description of these fossils is available. One of the largest collections of Tertiary sea turtle fossils in North America is from the Lee This content downloaded from 157.55.39.224 on Sat, 27 Aug 2016 04:05:15 UTC All use subject to http://about.jstor.org/terms C. K. DODD, JR. AND G. S. MORGAN