The popular name "spiny sharks" is a partial misnomer for these early jawed fishes. The name was coined because they were superficially shark-shaped, with a streamlined body, paired fins, a strongly upturned tail, and stout, largely immovable bony spines supporting all the fins except the tail - hence, "spiny sharks". However, acanthodians are not true sharks; their close relation to modern cartilaginous fish can lead them to be considered "stem-sharks". Acanthodians had a cartilaginous skeleton, but their fins had a wide, bony base and were reinforced on their anterior margin with a dentine spine. As a result, fossilized spines and scales are often all that remains of these fishes in ancient sedimentary rocks. The earliest acanthodians were marine, but during the Devonian, freshwater species became predominant.