File:Diorama of a Pennsylanian seafloor - Amphicentrum fish, sponge, crinoids, rugose corals 1 (45642213781).jpg

Seen here is a model-based reconstruction of life on an ancient seafloor during the Pennsylvanian Period - the "Age of Coal Swamps". This is a public exhibit at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania.

From exhibit signage:

Pennsylvania: a Tropical Paradise?

Between 286 and 320 million years ago, the Pennsylvanian Period, North America straddled the equator. The Pittsburgh/Tri-State area was a land of tropical forests, beaches, and vast seas. The waters were warm and rich with life. The sea level repeatedly rose and fell, due to plate movement and collisions, periodically covering large parts of North America.

The organisms shown above lived in these relatively shallow seas of less than 200 feet deep. The coastal areas teemed with micro-organisms. Distant relatives of today's sponges, corals, bryozoans, crinoids, and molluscs inhabited the bottom along with now exinct trilobites and ammonites, while primitive fishes swam above.

Sediments eroded from the young Appalachian Mountains were washed into the shallow seas. There, marine limestones, sandstones, and shales formed, often preserving as fossils the remains of many dead organisms. Also buried were millions of micro-organisms, which through heat and pressure were transformed into the fossil fuels, oil and gas, that serve the world today.