They are the earliest known resemblance of the Sharks that we know today. They are the first jawed vertebrates (have a backbone) and possess features such as fins and scales found in Sharks today! Although, the acanthodian had no teeth. The spiny shark’s head was small compared with its elongated body, and its eyes were very large. The snout region was very short, and it is evident that these fishes relied to a large extent upon sight rather than smell. An adult would grow up to 30 centimetres (12 in) long.