| Summary: | Shark teeth are the most abundant vertebrate fossil, and because tooth size generally correlates with body size, their accumulations document the size structure of populations. Understanding how ecological and environmental processes influence size structure, and how this extends to influence these dental distributions, may offer a window into the ecological and environmental dynamics of past and present shark populations. Here we examine the dental distributions of sand tigers, including extant Carcharias taurus and extinct Striatolamia macrota , to reconstruct the size structure for a contemporary locality and four Eocene localities. We compare empirical distributions against expectations from a population simulation to gain insight into potential governing ecological processes. Specifically, we investigate the influence of dispersal flexibility to and from protected nurseries. We show that changing the flexibility of initial dispersal of juveniles from the nursery and annual migration of adults to the nursery explains a large amount of dental distribution variability. Our framework predicts dispersal strategies of an extant sand tiger population, and supports nurseries as important components of sand tiger life history in both extant and Eocene populations. These results suggest nursery protection may be vital for shark conservation with increasing anthropogenic impacts and climate change. The anterior tooth length data from Eocene fossil sharks are labeled as the following columns: "Red_Hot" is the Red Hot Truck Stop locality of the Bashi/Tuscahoma Formations (Fm); Whiskey_Bridge is the Whiskey Bridge locality in the Stone City Member of the Crockett Fm.; Banks is Banks Island in the Cyclic Member of the Eureka Sound Fm. in the Arctic; Seymour is Seymour Island in the La Meseta Fm. of Antartica. The modern data from Delaware Bay takes total length data from the 2012 Delaware State and University of Delaware shark tagging program and transforms it to labial measurements of anterior tooth crown height (shown ...
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