This vertebrate trackway from the Coconino Sandstone was made by an unknown reptile or amphibian.

What is notable about this trackway is that the tracks mostly consist of toe marks, and these are oriented at an angle that is almost perpendicular to the line of travel.

In a field and laboratory study published in 1979, Dr. Brand created a controlled environment for amphibians and reptiles to make tracks on dry, damp, wet, and underwater sand. These tracks were then compared to fossil trackways collected from the Coconino Sandstone.

Observable toe marks, which are present in 80% or more of Coconino fossil trackways, were also present in the lab over 80% of the time when the animals walked on wet sand and underwater sand. Toe marks were only observed in less than 12% of tracks left in damp sand and dry sand. When the animals made tracks going uphill on dry sand, the tracks were little more than vague depressions, lacking discernible detail such as toe marks and foot shape. Although the tracks made on wet sand had visible toe marks, there were enough differing features when compared to the fossil trackways to suggest that it was unlikely that the Coconino trackways had been made in wet sand. Therefore, according to the lab results, dry, damp, and wet environments can be ruled out, while underwater sand appears to be the most likely environment to assign to the trackways of the Coconino Sandstone.

Brand (1979) found that partially buoyant animals in underwater conditions, “often push against the sand with their feet almost at right angles to the surface, rather than placing their feet flat on the surface. This produces tracks that usually have only toe marks or toe marks with a shortened sole impression” (p. 37). He also suggested that trackways where toes point in a different direction than the trackway orientation, “can perhaps be best explained by animals being pushed by a water current moving at an angle to the direction of their movement” (p. 37). This inference was confirmed by a subsequent study (Brand and Tang, 1991) where experimental trackways were produced with this distinctive characteristic.

Both of these features (toe marks with shortened sole impressions and angle between toe marks and trackway direction) are observed on Vertebrate Trackway GRI #442, suggesting that it was made by an animal that was drifting with a current as it moved over submerged sand.

In spite of dissenting views on this interpretation (Lockley et al., 1992: Marchetti et al., 2019), these particular features observed in some Coconino trackways remain an important piece of evidence that cannot be overlooked in paleoenvironmental reconstructions.

Based on the lithological characteristics, it is most likely that this slab was collected near Ash Fork, Arizona.

References:
Brand, L., 1979. Field and laboratory studies on the Coconino Sandstone (Permian) vertebrate footprints and their paleoecological implications. Palaeogeography, Palaeoclimatology, Palaeoecology, 28, pp.25-38. https://doi.org/10.1016/0031-0182(79)90111-1

Brand, L.R. and Tang, T., 1991. Fossil vertebrate footprints in the Coconino Sandstone (Permian) of northern Arizona: evidence for underwater origin. Geology, 19(12), pp.1201-1204. https://doi.org/10.1130/0091-7613(1991)019<1201:FVFITC>2.3.CO;2

Lockley, M.G., Loope, D.B. and Brand, L.R., 1992. Comment and reply on “Fossil vertebrate footprints in the Coconino sandstone (Permian) of northern Arizona: evidence for underwater origin”. Geology, 20(7), pp.666-670.

Marchetti, L., Voigt, S., Lucas, S.G., Francischini, H., Dentzien-Dias, P., Sacchi, R., Mangiacotti, M., Scali, S., Gazzola, A., Ronchi, A. and Millhouse, A., 2019. Tetrapod ichnotaxonomy in eolian paleoenvironments (Coconino and De Chelly formations, Arizona) and late Cisuralian (Permian) sauropsid radiation. Earth-Science Reviews, 190, pp.148-170. https://doi.org/10.1016/j.earscirev.2018.12.011