2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 18
Presentation Time: 8:00 AM-6:00 PM

Floating Islands as Taphonomic Agents In the Offshore Dispersal of Vertebrate Remains

HEINRICH, Paul V., Louisiana Geological Survey, Louisiana State Univ, 3079 Energy, Coast and Environment Building, Baton Rouge, LA 70803, heinric@lsu.edu

Since the mid-19th century, floating islands have been used to explain the long-distance transoceanic dispersal of terrestrial vertebrates. However, little thought has been given to the role of floating islands as an alternative taphonomic agent to the "bloat and float" model that is capable of transporting terrestrial vertebrate remains into marine environments.

Historic floating islands demonstrate that they are capable of the offshore transportation of large animals, which have become trapped on them. Once trapped on a floating island, an animal would typically eventually die, bloat, putrefy, and mummify. During this time, the floating island will protect the carcass from marine scavengers. These remains will rapidly sink once the floating island disintegrates. Instead of scattered bones created by the "bloat and float" model, the rafting and rapid sinking of such remains would deposit on the sea bottom a relatively articulated skeleton lacking evidence of either scavenging or predation and including articulated parts of limbs, tail, and peds.

Transport by floating island provides an alternative explanation for the anomalous occurrence of relatively articulated vertebrate skeletons found in marine deposits far from contemporary shorelines. Vertebrate fossils rafted by a floating island potentially include a therizinosaur skeleton recovered from the Tropic Shale of southern Utah; skeleton of the ankylosaur, Minmi paravertebra, found in the Allaru Mudstone of Queensland, Australia; skeleton of Scelidosaurus harrisonii found in the Lower Lias near Charmouth, England; skeletons of Niobrarasaurus coleii and Claosaurus agilis found in the Niobrara Formation within Kansas; and upside-down nodosaur described by Dr. O. C. Marsh from Como Bluff, Wyoming.

Animals, who are poor swimmers, would be preferentially trapped on floating islands relative to contemporaneous vertebrates, who are good swimmers. Thus, the relatively articulated fossils of poor swimmers, i.e. nodosaurs, might be found in marine deposits in unexpected numbers.