McMurdodus
The McMurdodus is considered the earliest known modern shark, which lived in the middle of the Devonian period about 390 million years ago. The classification is based on the tooth enamelooid, meaning it is more closely related to modern sharks than other extinct species.
These sharks were thought to be between 4.6 and 18 feet long. Most of their fossils have been found in Western Queensland, Australia. The closest living relative is believed to be the cowshark; however, scientists say there is nearly a 200 million-year gap in the fossil record between these two species.