DINOSAUR FOOTPRINT FROM THE UPPER
TRIASSIC ROCK POINT FORMATION OF THE
CHINLE GROUP, CANYONLANDS NATIONAL PARK
Spencer G. Lucas
New Mexico Museum of Natural History and Science
1801 Mountain Road, N.W.
Albuquerque, New Mexico 87104
Adrian P. Hunt and Martin G. Lockley
Department of Geology
University of Colorado at Denver
Denver, Colorado 80217
The first dinosaur footprint discovered in Triassic strata of the Canyonlands is a single Grallator footprint from the Upper Triassic Rock Point Formation near Upheaval Dome. This discovery further confirms the restriction of virtually all Late Triassic tetrapod footprints in the western United States to uppermost strata (Rock Point Formation and correlatives) of the Chinle Group.
Dinosaur footprints from the Upper Triassic Chinle Group have been reported from central Wyoming, northwestern Colorado, northeastern Utah and east-central New Mexico (Conrad et al., 1987; Hunt et al., 1989; Lockley et al., 1992, 1993; Lockley and Hunt, 1994 a, b). Dinosaur footprints have also been reported from the Chinle Group of eastern Utah, but they have not been described in as much detail as those from other areas (Lockley, 1986; Lockley et al., 1992). Here, we add to this record a dinosaur footprint discovered by the senior author near Upheaval Dome in Canyonlands National Park, Utah.
Upper Triassic strata exposed in Canyonlands National Park, Utah, belong to the Chinle Group of Lucas (1993). Here, Chinle Group strata disconformably overlie rocks of the Lower-Middle Triassic Moenkopi Group and are overlain disconformably by the Lower Jurassic Wingate Formation of the Glen Canyon Group. Southwest of Upheaval Dome in the Canyonlands, the Chinle Group section dips 20 degrees to N60 degrees E and is as follows (in ascending order): (1) Shinarump Formation, 16 m thick, trough-crossbedded extraformational conglomerate (clasts of chert, quartzite and Paleozoic limestone) and sandstone; (2) Cameron Formation, 9 m thick, thin, intercalated beds of ripple laminated sandstone and mudstone; (3) Blue Mesa Member of Petrified Forest Formation, 18.2 m thick, bentonitic mudstone and nodular calcrete, variegated green, red and purple; (4) Moss Back Formation, 7.6 m thick, trough-crossbedded and laminated intraformational conglomerate (sandstone and calcrete clasts) and sandstone; (5) Painted Desert Member of Petrified Forest Formation, 14.2 m thick, reddish brown bentonitic mudstone and siltstone; (6) Owl Rock Formation, 8.3 m thick, mottled pink and green, bioturbated siltstone; (7) Rock Point Formation, 64.9 m thick, reddish brown siltstone intercalated with laminated/ripple laminated sandstone except for the upper 9.2 m, which are the Hite Member, trough-crossbedded sandstone and siltstone-clast conglomerate.
The dinosaur track illustrated here was collected from the top of the bed just beneath the base of the Hite Member of the Rock Point Formation, a 0.6 m thick laminated sandstone. The locality is northeast of the loop trail from Upheaval Dome through Syncline Valley at UTM 4254500N, 591740E, zone 12, San Juan County, Utah.
The dinosaur footprint illustrated here (Fig. 1) was not collected. It is preserved as a concave mold in epirelief. The footprint has three toe impressions, the middle of which (impression of digit III) is much longer than the side toes (mesaxonic). All toe impressions have acute tips, and the posterior heel impression is pointed as well. Footprint length is 142 mm, and the angle of divarication of the digits is about 33 degrees. The track is an underprint, an no pad impressions are preserved. The tridactyl morphology, narrow, elongate digit impressions and impressions of clawed unguals of this footprint indicate that it is a theropod dinosaur footprint. Like most poorly preserved Triassic theropod footprints, this specimen is best assigned conservatively to the ichnogenus Grallator.
Hunt and Lucas (1992) first noted that virtually all Chinle Group tetrapod footprints are confined to the upper Rock Point Formation and its correlatives (also see Hunt et al., 1993). The Grallator footprint from the Rock Point Formation in Canyonlands further strengthens this conclusion. Where extensive footprint assemblages are known from the upper Chinle Group, theropod dinosaur footprints are the dominant track type (Lockley et al., 1992). Therefore, it is not surprising that a theropod footprint is the first tetrapod footprint found in the Rock Point Formation in the Canyonlands area. Lockley (1993a, b) and Lockley and Hunt (1994a) noted a marked increase in small grallatorid tracks in the upper part of the Chinle Group relative to other vertebrate track types. Therefore, they informally recognized a small grallatorid zone in the uppermost Chinle Group.
The footprint illustrated here remains in the field, and its conservation should be undertaken. Furthermore, this is the first dinosaur footprint found in Triassic strata in the Canyonlands. Its discovery should be an impetus to explore Rock Point Formation strata in the Canyonlands for additional tetrapod footprints.
The Superintendent of Canyonlands National Park permitted fieldwork in the Park. The National Geographic Society supported this research. Tom Goodspeed assisted in the field.
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Lucas, S.G., 1993. The Chinle Group: revised stratigraphy and biochronology of Upper Triassic nonmarine strata in the western United States: Museum of Northern Arizona, Bulletin 59, p. 27-50.
Figure 1. Footprint of theropod dinosaur, ichnogenus Grallator, from the Rock Point Formation of the Chinle Group near Upheaval Dome, Canyonlands National Park.
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