SHARK TAPHONOMY IN THE CLEVELAND SHALE OF NORTHEASTERN OHIO, USA: A STORY OF DISARTICULATION

Cladoselachian and ctenacanth sharks in the Cleveland Shale are known for being abundant and relatively well preserved. Can taphonomic condition be elucidated from their disarticulation? Preserved within cone-in-cone concretions, the shark fossils in this formation could provide clues towards their degree of disarticulation. Seven locally collected Cleveland Shale specimens were photographed and the fragments were digitally outlined. All specimens analyzed showed disarticulation, and were compared to a more completely articulated shark from the same formation. Thin section of the concretion confirmed entombing material is cone-in-cone.

The layout of these fossil assemblages shows a clear placement of remains in a near death pose. The arrangement of fragments show a pattern of minimal disarticulation with limited scatter. All seven specimens are incomplete despite the weak disarticulation.

The taphonomic sequence could be interpreted as death, gliding to bottom, coming to rest in a slight head-down pose, decay, unknown disturbance, burial, and then entombment in a concretion. The burial of the remains would have been gradual to allow for some decomposition as indicated by the removal of less substantial parts. The pattern of remains for each specimen indicates that the environment surrounding the shark’s burial site would have been ‘low-energy’ and anoxic. The remains are not scattered by currents or scavengers. It is possible that a hyper-saline current movement could have played a role in the disruption of the lighter body parts, leaving the more substantial remnants of the head (brain case, jaws, dorsal spine) while carrying away lower body segments (trunk and tail).