Sponges in Indiana Rocks (PA-22)
Sponges are among the simplest of animals. They represent the first advance of organisms above protozoans. They are some of the oldest organisms on earth, for their remains were found in a billion-year- old limestone. Sponges have always lived in marine waters.

Water pumped in and out of the sponges porous bodyn carries in particles of food and removes waste. The skeleton consists of small spicules of silica, lime or organic materials. The shape of sponges varies greatly, but the shape of the same species may vary with environment.

Fossil sponges are common in certain localities in Indiana. Specimens up to 20 inches in diameter and with a skeleton of tiny silica rods have been found in siltstones in Montgomery County. In younger Pennsylvanian rocks at a site in Warren County, sponge skeletons fell apart after great numbers of the animals died, and the sea floor was strewn with a mat of the spicules. Sponges with limy skeletons may make up a considerable part of some Indiana limestones.

Our Hoosier State Beneath Us: Paleontology