while the other suggests that they were actually some sort of ostracoderm agnathans. Timeline of genera See also Batoidea References Paleos Rhenanida Janvier, Philippe. Early Vertebrates Oxford, New York: Oxford University Press, 1998. Long, John A. The Rise of Fishes: 500 Million Years of Evolution Baltimore: The Johns Hopkins University Press, 1996. Prehistoric fish orders Early Devonian first appearances