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

 

 

ABSTRACT

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.

 

INTRODUCTION

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.

 

STRATIGRAPHIC CONTEXT

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.

 

IDENTIFICATION

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.

 

DISCUSSION

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.

 

ACKNOWLEDGMENTS

The Superintendent of Canyonlands National Park permitted fieldwork in the Park. The National Geographic Society supported this research. Tom Goodspeed assisted in the field.

 

REFERENCES

Conrad, K., Lockley, M.G. and Prine, N.K., 1987. Triassic and Jurassic vertebrate-dominated trace fossil assemblages of the Cimarron Valley region: implications for paleoecology and biostratigraphy: New Mexico Geological Society, Guidebook 38, p. 127-138.

Hunt, A.P., Lockley, M.G. and Lucas, S.G., 1993. Vertebrate and invertebrate trackways from Upper Triassic strata of the Tucumcari basin, east-central New Mexico, USA: New Mexico Museum of Natural History and Science, Bulletin 3, p. 199-201.

Hunt, A.P. and Lucas, S.G., 1992. Stratigraphic distribution and age of vertebrate tracks in the Chinle Group (Upper Triassic), western North America: Geological Society of America, Abstracts with Programs, v. 24, p. 19.

Hunt, A.P., Lucas, S.G. and Kietzke, K.K., 1989. Dinosaur footprints from the Redonda Member of the Chinle Formation (Upper Triassic), east-central New Mexico; in Gillette, D.D. and Lockley, M.G., eds., Dinosaur tracks and traces: Cambridge, Cambridge University Press, p. 277-280.

Lockley, M.G., 1986. A guide to dinosaur tracksites of the Colorado Plateau and American Southwest: University of Colorado at Denver, Geology Department Magazine, Special Issue 1, 56 p.

Lockley M.G., 1993a. Auf der Spuren der Dinosaurier: Birkhauser, 312 p.

Lockley, M.G., 1993b. Siguiendo las huellas de los dinosaurios: McGraw Hill, 307 p.

Lockley, M.G. and Hunt, A.P., 1994a. A review of vertebrate ichnofaunas of the Western Interior United States; in Caputo, M.V. and Peterson, J.A., eds., Mesozoic systems of the Rocky Mountain region, United States: Denver, RMS-SEPM, in press.

Lockley, M.G. and Hunt, A.P., 1994b. Dinosaur tracks and other fossil footprints of the western United States: New York, Columbia University Press, in press.

Lockley, M.G., Conrad, K., Paquette, M. and Hamblin, A., 1992. Late Triassic vertebrate tracks in the Dinosaur National Monument area: Utah Geological Survey, Miscellaneous Publication 92-3, p. 383-391.

Lockley, M.G., Santos, V.F. and Hunt, A.P., 1993. A new Late Triassic tracksite in the Sheep Pen Sandstone, Sloan Canyon, New Mexico: New Mexico Museum of Natural History and Science, Bulletin 3, p. 285-288.

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.

Back to Table of Contents

United States Department of the Interior, National Park Service

Go to Nature Net Home Page Go to Park Net Home Page