A TREASURE TROVE OF TRIASSIC TRACKS: REPTILE FOOTPRINT FOSSILS IN THE MOENKOPI FORMATION REVEALED BY TWO SCIENTISTS IN PARKS SURVEYS AT WUPATKI NATIONAL MONUMENT, NORTH-CENTRAL ARIZONA

Wupatki National Monument (WUPA) in north-central Arizona preserves extensive exposures of the Moenkopi Formation, coastal plain and fluvial deposits that record Early–Middle Triassic time in western Pangea. A diverse, reptile-dominated vertebrate ichnofossil assemblage has been documented in the Moenkopi Formation throughout southwestern North America, as well as in Lower–Middle Triassic strata globally. However, there was only one known vertebrate ichnofossil site in WUPA as of 2000, and only five by mid-2020, with virtually all of the park unsurveyed.

Two years later, after two Scientists in Parks surveys, there are now 37 known vertebrate ichnofossil sites in WUPA. Most sites are reptile tracks/trackways preserved as casts on the base of sandstone beds and the lower bedding surface of fallen blocks, although several ichnofossil molds on upper bedding surfaces were also found. The sites in WUPA preserve at least seven reptilian ichnogenera: Chirotherium, Synaptichnium, Rotodactylus, Rhynchosauroides, Procolophonichnium, Isochirotherium, and Protochirotherium. Identifications that have been made at the ichnospecies level include Chirotherium rex, C. barthii, C. sickleri, Synaptichnium diabloense, S. cameronense, Rotodactylus cursorius, Isochirotherium marshalli, and I. coltoni.

Invertebrate ichnofossils in WUPA have been identified as Lockeia cunctator, Bergaueria hemispherica, Planolites, Rhizocorallium, and Koupichnium. One body fossil occurrence was found, consisting of numerous small bone fragments in a pebble conglomerate bed. Three plant fossil sites were also found, two of them at sites with vertebrate ichnofossils.

The vertebrate and invertebrate ichnofossil assemblage at WUPA, as well as the plant and body fossils, provide crucial information about the paleoenvironment and paleoecology of western Pangea during Early–Middle Triassic time. Detailed features preserved at several WUPA sites include skin impressions, claw impressions, scale-mark striations, and tail drags. Several trackway sites provide important data such as the stride and pace angulation of the animal. Now that an initial inventory of WUPA is complete, the discovered sites can be monitored into the future to protect these irreplaceable scientific and educational resources.