PLIOCENE FOSSIL NODIPECTEN SCALLOPS FROM SOUTH CAROLINA

The two Pliocene fossil Nodipecten scallops from South Carolina are Nodipecten collierensis (Mansfield, 1932) from the Lower Goose Creek Limestone and Nodipecten peedeensis (Tuomey and Holmes, 1855) from the Upper Goose Creek Limestone. N. collierensis has been documented by numerous specimens from the Lower Goose Creek Limestone in Berkeley and Charleston counties in South Carolina. N. collierensis has one specimen reported from Lake Waccamaw, NC, abundant specimens from south Florida, abundant specimens from Venezuela, and possible reports from Haiti and the Dominican Republic. All known specimens of N. collierensis from South Carolina have seven ribs on the left valve to interlock with eight ribs on the right valve.

Nodipecten peedeensis (Tuomey and Holmes, 1855) is known from a total of six published specimens, plus twelve additional specimens in the Charleston Museum. One right valve had six ribs, and the other seventeen specimens had seven ribs on the left valve interlocking with eight ribs on the right valve. This one specimen is the only published fossil or Recent Nodipecten with a pattern of fused ribs to produce a low rib count. A population of 183 specimens from Horry County, SC added 47 specimens with fused ribs and a low rib count. Out of 201 total specimens, 48 specimens (24%) had one or two ribs fused on the right valve giving a count of seven ribs on the right valve interlocking with six ribs on the left valve or a count of six ribs on the right valve interlocking with five ribs on the left valve. The frequency of 24% is suggestive of a Mendelian population genetics ratio for a recessive phenotype.

Out of 201 total specimens of Nodipecten peedeensis, 61 are paired specimens, 91 are single right valves, and 49 are single left valves. It is expected that more right valves than left valves would be preserved based on life position. The shallow marine carbonate depositional environment preserved an unusually high number of specimens as articulated pairs, suggesting rapid burial.