While Dunkleosteus is one of Ohio's most famous Devonian fossils, it is far from the most common. Some of the most common Devonian fossils are rugose corals, also known as horn corals. Often mistaken for teeth, these extinct corals were solitary corals; imagine a cone with a polyp on top. Horn corals would have been important and abundant reef builders during the Devonian Period, and they provide vital clues as to what life was like at that time. For example, they provide evidence that the Earth’s rotation has slowed. Corals have regular growth rates, producing around one growth band per year. Paleontologist John W. Wells discovered that the growth lines on horn corals suggest there were about 400 days a year during the Middle Devonian Period, indicating that the Earth once rotated more quickly.
