A new study by researchers at the University of Minnesota Twin Cities challenges existing paleontological classifications used to determine how the fossil record is formed. The investigation focused on how dinosaur and mammal bones are transported and buried by floodwaters to understand how animal remains may disperse prior to fossilization. This research offers new insights for understanding animal extinction and environmental changes. The paper was published in Paleobiology.
The researchers tested bone movement under unsteady flow dynamics, characteristic of natural sheet floods. These conditions are frequently cited in paleontological literature as dispersal agents but differ significantly from the typical river flow conditions used in previous transport experiments. Historically, flood events were often proposed to explain animal burial, but the specific details of these events had not been extensively explored.
Michael Chiappone, a University of Minnesota Ph.D. candidate and the study's lead author, stated that paleontologists endeavor to reconstruct the formation of fossil sites. The team questioned whether fossil organisms are preserved at their death locations or if they are moved by scavengers or water flow post-mortem.
Utilizing facilities at the University of Minnesota's St. Anthony Falls Laboratory, the team simulated surging waves of water that reproduced real-world floods and river features such as ripples, dunes, and bars in full-scale experiments. These tests allowed them to determine how bones sort in water flow based on their sizes, shapes, and densities.
The findings indicated that heavy elements, such as articulated skulls, exhibited minimal movement, while other bones, like hip bones, tended to move further, sometimes exiting the experimental area. The overall data suggests that during typical seasonal floods, many bones do not travel far from where the animal died, unless the flood was exceptionally powerful or the bones were very small.
By recreating actual flood conditions, the study demonstrates that how water moves and interacts with the riverbed can sort bones in ways that do not always align with the traditional Voorhies classification system, which is used to predict which bones are most easily carried by flowing water. This new information encourages paleontologists to consider additional variables when reconstructing extinct animals and their past environments.
Peter Makovicky, a professor and paleontologist in the University of Minnesota Department of Earth and Environmental Sciences and senior author of the paper, noted that the experimental results will assist in interpreting how bones were sorted, accumulated, and buried at paleontological excavation sites. This provides foundational information for reconstructing extinct animals and their habitats.
The team has plans for further experiments on a wide variety of bones and aims to expand this research to include extremely large bones found in animals such as elephants, whales, and bison. The research team also included Michele Guala and Raymond Rogers. The full paper is titled "When the Levee Breaks: Experimentally Testing Dinosaur and Mammal Bone Transport in Unsteady Flows."