Cylindracanthus is an extinct genus of Cretaceous to Eocene aged
ray-finned fish. It is almost exclusively known from bony
rostrum fragments as well as some associated teeth, with the rest of the skeleton being cartilaginous. While originally considered to be closely related to
billfish, the structure of its rostrum is dissimilar, and is unlikely to be closely related, some later studies suggested closer affinities to the
Acipenseriformes.[1][2][3] However, this was later rejected due to the lack of
osteocytes in histologically examined specimens, which resembles the condition of derived
teleosts. A close relation to Blochius has been suggested.[4]
^Parris, D. C., Grandstaff, B. S. and Bell, G. L. 2001. Reassessment of the affinities of the extinct genus Cylindracanthus (Osteichthyes). Proceedings of the South Dakota Academy of Science, 80: 161–172.
^Parris, D. C., Grandstaff, B. S. and Gallagher, W. B. 2007. “Fossil fish from the Pierre Shale Group (Late Cretaceous): clarifying the biostratigraphic record”. In The Geology and Paleontology of the Late Cretaceous Marine Deposits of the Dakotas, Edited by: Martin, J. E. and Parris, D. C. 99–109. Geological Society of America. Special Paper 427