5" Pennsylvanian Fossil Brachiopod Plate - Kentucky

The Breathitt Formation produces both marine and land fauna/flora fossils, for about 300 million years ago this region was a river delta next to the sea. During this period of deposition, repetition of shallow seas incoming and receding resulted in marine layers between the coal, sandstone and plant shale layers. These marine layers primarily contain brachiopods, however trilobite fossils have been reported in locations near this site.

Brachiopods are members of the phylum Brachiopoda. They are clam-like with wide shells composed of two halves called valves. They are filter feeders that live a-fixed to rocks or on the seafloor. Brachiopods first appear in early Cambrian. These were simple forms with non-articulating shells. Their diversity peaked during the Devonian and there are currently 12,000 described fossil species of Brachiopoda from 5,000 genera. Most species of brachiopod died out during the Permian-Triassic Extinction but there are about 450 species living today. They live in cold, marine environments, like polar seas or the continental shelf and slope. The largest fossil Brachiopod is 7.9 inches (200 mm). Most are 2-4 inches (3-8 cm). Living Brachiopods also fall into this range.

Brachiopods are more closely related to Bryozoans than Mollusks. The easiest differences to identify are in the shells of clams and Brachiopods. Mollusk shells are divided into left and right while Brachiopod shells are divided top (dorsal) and bottom (ventral). The shells of mollusks are usually equal on the right and left. In Brachiopods, the bottom shell is larger than the top. The other big difference is in how they feed. Both are filter feeders but mollusks extend their filter into the water and pull food into its shell. Brachiopods have internal feeding structures. Water is drawn into the shell where the food is filtered out before expelling it out.