Introduction: Species diversity is linked to habitat conditions and can change with environmental modifications. Stable, less severe environments typically have higher species diversity than more extreme environments. Indices of species diversity are relative numerical values that reflect the variety of species present and their relative abundance. Simpson’s Index, for example, would reflect a higher diversity for a sample with 5 species with counts of 4,4,4,4, and 4 compared to a sample with 5 species with counts of 50,1,1,1, and 1. Simpson’s index ranges from 1 to infinity.

Compute Simpson’s index (D) using the equation:

            D = [N(N-1)] / (S n_i (n_i-1))

Where:   D = Diversity Index.

                N = total number of individuals for all species.

                n_I = number of individuals in each species.

                S = sum of the products for all species.

Example: Two species with 10 individuals each are found in a sample.

            D = (20(19))/180 = 2.11

1. Compute the diversity index for the class data. Compare that to the diversity index for your group. What might account for the differences in the indices?
2. What plant and animal ecological groups are missing from this fossil community? What are some potential explanations for their absence?
3. Theoretically reconstruct this prehistoric coastal marine ecosystem. Most of these fossils are from the highest carnivore trophic levels (except for most of the whales). Using the data related to modern-day sharks (in the table below), determine what species groups might have been present in the lower trophic levels fed upon by your sharks.
4. Using the fossil teeth from extinct species, determine what food types might have been in their diets. Triangular teeth with serrated edges are better adapted for tearing or sawing large quantities of flesh from larger prey. Narrow pointed teeth are adapted for snagging fast-moving prey (such as bony fish).

Shark Species	Common Food Items
Bull, Carcharhinus leucas	Bony fish, small sharks
Mako, Isurus oxyrinchus	Bluefish or similar smaller bony fish, squid
Tiger, Galeocerdo cuvier	Sea turtles, bony fish, marine mammals, crustaceans
Great white, Charcarodon carcharias	Marine mammals, seals, dead whales, sharks and bony fish
Sand tiger, Eugomphodus taurus	Bony fish

Click here to see the shark tooth key.