150


Journal of Paleontology 90(1):147–153


Figure 3. (1) Late Paleocene to early Eocene geomagnetic polarity scale and calcareous nannofossil zonation. Calcareous nannofossil stratigraphy is based on the zonation of Martini (1971). The timescale is based on Vandenberghe et al. (2012). Upward-pointing triangles indicate first-occurrence datums; downward- pointing triangles indicate last-occurrence datums. Dashed lines indicate possibly diachronous datums. (2) Paleocene strata within the Outer Coastal Plain of South Carolina. Gray areas represent unconformities. Modified from Weems and Bybell (1998). The glyptosaur fossils occur within the upper part of the Chicora Member of the Williamsburg Formation (subzone NP9a, latest Paleocene).


presence of Discoaster multiradiatus Bramlette and Riedel, 1954, which has its first occurrence at the base of NP9a, and the absence of Discoaster araneus Bukry, 1971, which marks the base of subzone NP9b, and thus constrains the sample to sub- zone NP9a. In addition, the presence of common Hornibrookina arca Bybell and Self-Trail, 1995 and Prinsius bisulcus (Stradner, 1963), and the absence of Rhomboaster spp. and Bomolithus supremus Bown and Dunkley Jones, 2006, supports the conclusion that these sediments were deposited just prior to the Paleocene/Eocene boundary (Fig. 3.1; Self-Trail et al., 2012). There is no evidence of mixed-age assemblages, sug- gesting that reworking and/or contamination is not an issue. The Jamestown deposit is therefore temporally equivalent


to the Chicora Member (NP8 to NP9a) of the Williamsburg Formation as reported in northwestern Berkeley County (Fig. 3.2), and most of the lower vertebrates reported from the Williamsburg Formation (Hutchinson and Weems, 1998; Purdy, 1998; Weems, 1998; Weems and Bybell, 1998) have been recovered in the Jamestown deposit. In Berkeley County, the Chicora Member may be disconformably overlain by Pleistocene strata, whereas in southern Dorchester County it is disconformably overlain by the Fishburne Formation (NP11; Harris and Zullo, 1991; Edwards et al., 2000). Edwards et al. (2000) noted that the Chicora Member disconformably


underlies the Santee Limestone in northern Dorchester County, and the Santee Limestone also overlies the fossiliferous deposit at the Jamestown site (fragments of Santee Limestone show that late Paleocene fossils were reworked into the Eocene deposit). The fossiliferous Jamestown deposit is lithologically and paleontologically similar, and temporally equivalent, to the Chicora Member, and at this time it is most parsimonious to identify the deposit as this lithostratigraphic unit.


Geographic significance of find.—No major mountain range or, after regression of the Cannonball Sea by the middle Paleocene (Boyd and Lillegraven, 2011; Weems, 2014), epeiric sea posed a barrier to inhibit eastward migration of glyptosaurines in North America, and the South Carolina fossils show that these lizards were established along the southeastern coastal margin of the United States by the latest Paleocene (57 Ma). To our knowledge, the South Carolina specimens thus far represent the only unequivocal Cenozoic occurrence of these lizards from east of the Mississippi River. McKenna (1975) argued for an early Eocene continuity


between North America and Europe, and two early Eocene routes linking these two regions are recognized (Hooker, 2007; Eberle and Greenwood, 2012). Discoveries of early Eocene glyptosaur fossils on Ellesmere Island (Estes and Hutchison,


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