Leonard R. Brand, Thu Tang; Fossil vertebrate footprints in the Coconino Sandstone (Permian) of northern Arizona: Evidence for underwater origin. Geology ; 19 (12): 1201–1204. doi: https://doi.org/10.1130/0091-7613(1991)019<1201:FVFITC>2.3.CO;2
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Numerous fossil vertebrate trackways in the Coconino Sandstone of northern Arizona exhibit several features that imply that these trackways were not made in subaerial conditions. Some trackways begin or end abruptly on undisturbed bedding planes, and in other trackways the individual prints are oriented in a different direction from that of the trackway. These features indicate buoyancy of the animals in water. The animals were swimming in the water part of the time and at other times walking on the substrate, and they were sometimes orienting upslope on the surface of the underwater dunes, while being drifted sideways by lateral currents. Observations on salamander locomotion in a sedimentation tank with flowing water support this model.