Drilled Shells and Crowded Rocks: Interactions in a Fossil Hall

Eat, Compete or Cooperate

1A new exhibit in the fossil hall of the Harrow Point Museum of Natural History shows how living things affect each other, today and long ago. Seventh grader Elif Demir volunteered there all summer, helping paleontologist Dr. Sunita Raghunathan sort fossils and gather data for three cases in the exhibit.

2Case 1 holds fossil clam shells from three rock layers in a sea cliff, all about 3 million years old. The lowest layer is the oldest. Living moon snails are sea snails that wrap a clam in their large foot, scrape a small round hole through its shell and eat the soft body inside. Their holes are neat circles that are wider on the outside of the shell than on the inside. Elif sorted the clam shells and moon snail fossils from one bucket of rock from each layer. She also sorted the clam shells from the upper layer by size.

3Case 2 is a “Then and Now” display about a rocky shore today. Two kinds of barnacles live there, glued to the rock, filtering bits of food from the water. Young barnacles of both kinds settle in the middle zone of the shore. The large kind grows fast, and as it grows it can crowd against small barnacles and pry them off the rock. Scientists cleared all the large barnacles from some patches of rock in the middle zone and left other patches alone. After one year they counted the small barnacles still alive in each patch.

4Case 3 shows a yucca plant and a small white moth. A female yucca moth gathers pollen from one yucca flower, flies to another, and presses the pollen onto it. Then she lays a few eggs inside the flower. Pollinated flowers grow into pods full of seeds, and the moth larvae that hatch feed on some of the seeds before crawling out. In the desert region shown in the exhibit, yucca flowers are pollinated almost only by these moths, and the moth larvae feed only on yucca seeds. Elif opened three ripe pods and counted their seeds.