COMPARING BODY SIZE OF THE SAND TIGER SHARK STRIATOLAMIA MACROTA FROM EOCENE LOCALITIES IN NORTHERN CANADA AND MISSISSIPPI

Shark teeth are the most abundant vertebrate fossil in the geologic record and can provide remarkable insight into the past. Among the most abundant fossil shark teeth found during the early Eocene Epoch (ca. 55-50 Ma) are those belonging to the extinct sand tiger shark Striatolamia macrota. In this study, we measured the length of anterior S. macrota teeth from mid- and high-latitude localities in North America as a proxy for body size. Thousands of fossil shark teeth were found on northern Banks Island (BI), Canada, in the Cyclic Member of the Eureka Sound Formation, and in an early Eocene fossil locality in Meridian, Mississippi, known as the Red Hot Truck Stop (RHTS). Both localities were a warm, nearshore deltaic environment that contained a vast amount of S. macrota. Given these similar, environments we hypothesized S. macrota at both localities would be comparable in size. Approximately 400 anterior teeth from each locality were measured and compared in order to determine if they had similar-sized sand tiger sharks during the early Eocene Epoch. The mean length of the anterior teeth from BI was 13.70 mm, whereas the mean length from the RHTS was only 11.60 mm. In addition, the BI teeth have a higher density of teeth larger than 16 mm, whereas the teeth from the RHTS have a much higher density of teeth smaller than 14 mm. Teeth measured from both localities were also shown to have two relative maxima. This may represent teeth from the upper and lower jaws or capture the teeth of males and females. A plausible explanation for the size difference may be latitudinal differences. According to Bergmann’s rule, individuals living in colder temperatures are larger than individuals inhabiting warmer temperatures. Therefore, the body size of individuals increases with latitude. The abundance of S. macrota in both brackish and marine coastal environments across latitudes during the Eocene suggests a wide range of environmental tolerances than what is reflected in today’s sand tiger shark distribution, which bodes well for their ability to adapt to future environmental change.