There were seven groups of Hemipristis serra teeth used in this study, examples of five are illustrated in Figure 2, with measurements detailed in Table 1. Three groups were purely float samples (collected in overburden removed by mining operations): 51 specimens from the Belgrade Formation, 102 from the Pungo River spoil piles, and 193 from the Yorktown Formation spoil piles. The Pungo River and Yorktown specimens were collected in the PCS Phosphate Mine (Lee Creek) near Aurora, North Carolina, whereas the Belgrade material was collected in the Belgrade Quarry near Maysville, North Carolina.

These three float collections were obtained by experienced collectors, familiar with the appearance of the various formations' sediments. While it is thought that the overwhelming majority of each sample is pure, it is possible, perhaps even likely, that any of the three samples could be contaminated with teeth not from its labeled formation; some mixing is inevitable in mine/quarry operations. One of the points of this research is to show that useful information may be obtained even though some of the specimens likely have questionable data. However, it would be virtually impossible to collect enough specimens for this kind of study using careful, in situ screening: the mine operators would not allow the concomitant interruption of operations. There are no known surface exposures of Pungo River Foramation sediments in North Carolina; the only access is in the Lee Creek Mine. While there are a few surface exposures of the Yorktown (Snyder et al. 2001) and Belgrade Formations (Harris and Zullo 1991), specimens are not highly concentrated. The amount of excavation required to collect nearly 450 teeth in situ would be staggering.

Some familiarity with the mining operation at the Lee Creek Mine is necessary to understand the fourth collection of teeth in this study. To gain access to the ore (which lies approximately 30-35 m below sea level) the top 10 or so meters are removed using a bucket-wheel excavator and transported on a conveyor belt to a previously mined pit. The next 20-25 m are removed by large electric draglines and piled in the immediately previous cut. This "topside-down" process results in the older sediments generally being placed on top of younger ones in the spoil piles, but some mixing inevitably occurs. Once the mining equipment is removed to safe distances, specimen collecting is allowed on the spoil piles under tightly regulated conditions. These 25-30 m of spoils contain the Croatan (also known as the James City) Formation shell bed, the various levels of the Yorktown Formation, and the top level of the Pungo River Formation. This very fossiliferous level, the so-called Coquina Bed and source of the Pungo River float sample described above, consists of interbedded soft to indurated marly gray clay, a white moldic limestone, and rich black clayey phosphatic sand. The limestone's nearly white color makes it an easily recognized indicator to the dragline operators that the ore matrix has been reached. The operators are also very careful not to breach the bottom boundary of the ore matrix, a hard, dolomitic sandstone known as the caprock, as that would allow the influx of water from the underlying Castle Hayne aquifer (see Figure 3).

The ore is piled beside the dragline, sprayed with high-pressure water to break up large aggregations, and the water-ore slurry is pumped to the processing plant. At the plant the slurry is screened to remove the larger non-ore materials. This so-called reject material contains shark teeth (and other marine fossils) in great abundance. The fourth sample of 101 teeth was collected from this reject material. It is a far more homogeneous sample than the previously described float-collected Pungo River material, coming almost exclusively from the ore layer. Technically, however, it is also a float sample, its source being disturbed sediments.

A fifth collection of 32 teeth (lent by the Calvert Marine Museum) was collected in situ from various Shattuck Zones in the Calvert Formation, and fairly precise age data is available on individual teeth. The sixth sample group consisting of eight teeth from the Eocene species Hemipristis curvatus was collected from the Santee Limestone exposed in the Giant Cement Mine near Harleyville, South Carolina. The seventh group, 30 teeth from the Recent species, Hemipristis elongata, was purchased from a commercial dealer and originated in Indonesia.

Measurement data from the four float samples (Belgrade, Pungo River float, Pungo River reject, and Yorktown) are used in the statistical modeling procedures below. The Calvert sample is used in an effort to validate or refine the models. Data from the two non-serra species is used to discover how sensitive the models are with regard to species.

The Pungo Float, Yorktown, Santee, and Recent samples are housed in the North Carolina Museum of Natural Sciences in Raleigh. The Belgrade sample is part of the personal collection of Mr. G. Fonger of Gaithersburg, Maryland, and was collected over a period of many years in areas of the Belgrade Quarry now off-limits to collectors. The Pungo Reject sample was collected by K. and P. Young of Edward, North Carolina, during one month in the spring of 2004 from the reject pile adjacent to the PCS plant at the Lee Creek Mine. This resource is off-limits to all but a very few persons specifically permitted by PCS. After scanning, this sample was returned to the Youngs. High-resolution (600 dpi) scans of the labial side of all the specimens used in this study are available (in TIFF format) from the first-named author (REC).