Radiological Health Department, University of Utah, Salt Lake City, UT 84112
Abstract To date, our knowledge of the large terrestrial vertebrae faunas on the western shore line of the Cretaceous sea way in Central Utah, from the Middle Cretaceous Albian period to the Upper Cretaceous Campanian period, remains sparse. This is due in part to taphonomic bias ( lack of preservation), as well as the paucity of exposed strata. The result is large gaps, in the faunal record, notable in the large vertebrae faunal record. An example is the Ferron Sandstone Member of the Mancos Shale Formation, Eastern-Central Utah. The Ferron Sandstone Member is a thin strip of exposed coastal plain on the western shore of the Cretaceous sea. The Ferron Sandstone Member is Middle to Upper Turonian age (Franczyk 1991) and not noted for vertebrae fossils or track. The Upper Turonian age is a mid point in the dinosaur faunal gap between the Middle Cretaceous Albian period and the Upper Cretaceous Campanian period. The Moore Trackway (described herein) represents an ornithopod dinosaur that walk the coastal plain approximately ninety million years ago. The location of the trackway exposes it to a high probability of vandalism.
The Ferron Sandstone Member of the Mancos Shale Formation of Eastern Utah, a coastal plain environment, is not noted for vertebrae fossil bone or tracks. While other late Cretaceous coastal plain environments such as the later Upper Cretaceous (Campanian) Blackhawk Formation (Doelling, 1972) from the Mesaverde Group and the earlier, Lower Cretaceous (Albian) Dakota Sandstone Formation, do not contain fossilized bone. But do contain an abundant of vertebrae tracks. Most of the tracks in the Dakota Sandstone Formation are found in Colorado along what was once the eastern shore line of the Cretaceous Sea. While there is an abundance of tracks in the Dakota Sandstone in Colorado, the Dakota Sandstone Formation along the western shore line of the Cretaceous Sea contains very few tracks.
The tracks in the Dakota Sandstone ( Lockley and Hunt, 1995) and the Blackhawk Formation (Parker and Rowley, 1989) give paleontologists an understanding of the large terrestrial vertebrae faunas that inhabited the eastern shore line of the Cretaceous Sea during the Middle Cretaceous (Albian) and the western shore line during the Upper Cretaceous (Campanian). Understanding of the large terrestrial vertebrae faunas on the western shore line from the late Middle Cretaceous (Albian) to the late Upper Cretaceous (Campanian) is as yet poorly documented. Tracks in the Ferron Sandstone during the Middle to Upper Turonian in Utah are rare.
This purpose of this paper is to report on a vertebrate trackway of late Cretaceous age, in the Ferron Sandstone Member of the Mancos Shale Formation (Middle to Upper Turonian) (Hintze, 1982). A picture and caption of this trackway are briefly mentioned in DeCourten (1998).
The trackway was shown to the author in 1998 by Jim Nielsen from Castle Dale, Utah. The trackway is located along side of a graveled road. This road runs between the almost ghost town of Moore and Interstate highway I-70 in Emery County, Utah. Hereafter, the site is refer to as the Moore Tracksite.
Figure 1. The stratigraphic position of the Moore Track site in the Ferron Sandstone Member of the Mancos Shale Formation of Eastern Utah, (Hintze, 1982).
The Ferron Sandstone Member, a delta /coastal plain environment, is a regressional sequence of the Great Western Interior Seaway sometimes is referred to as the Cretaceous Seaway (Ryer, 1991). The age of the Ferron Sandstone Member of the Mancos Shale Formation is Late Cretaceous (Middle to Upper Turonian) (Hintze, 1982).
The Ferron Sandstone Member on the western side of the San Rafael anticline dips to the west with a North-South strike. Thus, the Ferron Sandstone forms an erosion resistant escarpment that is exposed for long periods of time, allowing for the formation of what is referred to as desert varnish. Desert varnish consists of a blue-black veneer of iron and manganese oxides that commonly forms on exposed sandstone in arid climates.
The trackway runs across the top of a 10 X 5 meter wide and 2.5 meter thick block of sandstone. It appears that the block has fallen from the Ferron Sandstone escarpment located directly to the north of the trackway. The top of the block has a coating of desert varnish, indicating that the trackway had been exposed to the environment for a long period. The desert varnish and the thickness of the block provide evidence that this block of sandstone came from the very top of the Ferron Sandstone escarpment, which was the last oscillating sequence in the disposition of the Ferron Sandstone Member of the Mancos Shale Formation (Ryer, 1991). The top of the Ferron Sandstone Member is Upper Turonian age, which is approximately 90 million years old. Therefore the Moore Trackway (Fig. 1) is very likely of Upper Turonian age.
MORPHOLOGY OF TRACKS
Vertebrate tracks are preserved as: 1- natural casts, made by the infilling of sediments after the print was made, 2- original prints or tracks, and 3- undertracks, made by the pressure of the original impression being transmitted to an underlayer beneath the original sedimentary layer (Lockley and Hunt, 1995). The Moore Trackway consists of original prints or tracks and natural casts.
THE MORPHOLOGY OF THE MOORE TRACKWAY
The trackway (Fig. 2) consists of nine tridactyl foot prints, five of the left pace and four of the right pace made by a single animal. There is no evidence of fore, prints which indicate that the animal was bipedal. The tracks are not well defined. The only character that is consistently defined (in three of the tracks) is the toe print on the medial side on the left pace. The lengths for tracks number 1, 3 and 7 varied from 18cm to 40cm. This variation in the track's length is due to the fact that the posterior edge of the tracks are not well defined. This variation could also be due to metatarsal impressions or heel scrapes which tends to elongate the track (Lockley and Hunt, 1995).
The track widths varied from 18cm to 27cm, once again, the lateral edges of the tracks are not well defined, causing the widths of the tracks to vary. Some of the tracks as viewed laterally are domed-shaped, with the thickest section of the dome at the posterior edge. The thickness decreases as the anterior end of the track is approach.
The footfalls in the Moore Trackway show a consistent 97cm length in the left and right paces. The widths between the left paces and right paces are a consistent 16 cm. The width between the tracks, is so narrow that the medial edge of the prints are close to or touching the mid line of the trackway.
Figure 2. The Moore Trackway in the Ferron Sandstone Member of the Mancos Shale Formation of Eastern Utah.
#1 Domed track, #2 Dished out track, #3 Domed track, #4 Indistiguishable track, #5 Domed track, #6 Indistinguishable track, #7 Domed track, #8 Domed track, and #9 Dished out track.
It is unlikely that we will be able to identify with certainty the maker of the Moore Trackway. The identification of the vertebrate trackmaker is problematic because only exceptionally well preserved tracks can be used identify taxa and even these identifications are uncertain unless the fossilized bones of the animal are found in the same strata, even then it is difficult to be confident. The preservation of foot prints in the Moore Trackway is insufficient to identify the taxa below the level of or that there will not be any attempt the identify the animal below the level of ornithopod.
There are some characters that the tracks do reveal about this animal. The prints show the 2nd and 3rd digit indicating that animal was tridactyl. The major differences between ornithopod tracks and theropod tracks, is that the theropod track has claw impressions (yet claws impressions do not always show up in mud) and the ornithopod track has a more square heel or metatarsal impressions. The Moore Trackway prints show no claw impressions and the posterior edge is square or blunt shape. These characters suggest that the track maker was an ornithopod dinosaur (Gillette and Lockely, 1989).
The trackway width is narrow, suggesting that the animal walked with an upright stance as dinosaurs do rather than the reptilian sprawling stance (Wade, 1989). The footfalls in the Moore Trackway show a consistent 97cm length in the left and right paces. This consistency in the sequences of footfalls in the track-way implies that the trackmaker used a regular or symmetrical gait and was probability walking rather than running. Trackway evidence suggests that dinosaurs, like other vertebrates, typically moved at slow speeds (Thulborn, 1982).
The hip height of the animal can be estimated multiplying the length of the print by 4 (Alexander, 1976) for a small ornithopod and by 5.9 for a large ornithopod. The print length for the Moore Trackway assuming no heel scrape is 18 cm and assuming it is a small ornithopod, an estimate of hip height for the animal would be 4 X 18 cm = 72 cm. The 3rd digit is slightly off set laterally from the pace center line indicating that the animal`s feet rotate inward slightly as the animal is walking. This is a character of ornithopod.
Figure 3. Comparative stratigraphy of vertebrate track-bearing Cretaceous rocks deposited along the western shore line of the Cretaceous Sea in central Utah.
The Upper Turonian age of the Moore Trackway is what makes this trackway important. The Upper Turonian age is a mid point in the dinosaur faunal gap between the Middle Cretaceous Albian period and the Upper Cretaceous Campanian period (Fig. 3). The Moore Trackway basically says that an animal walked this coastal plain ninety million years ago, and that animal was more than likely a ornithopod dinosaur. This adds one more piece to puzzle of the large terrestrial vertebrae faunal along the western shore of the Cretaceous Sea Way during the Upper Turonian age .
Scott D. Sampson Ph.D., for reviewing this paper. Bill and Judy Peterson, for track site measurements and documentation. Dr. Lehi F. Hintze, for permission to use the stratigraphic column in Figure 1.
Alexander, R.M., 1976. Estimates of speeds of dinosaurs. Nature 261: 129-130.
DeCourten, F., 1998. Dinosaurs of Utah, University of Utah Press, Salt Lake City, Utah. pp 213.
Franczyk, K.J. and J.K. Pitman, 1991. Latest Cretaceous Nonmarine Depositional system In The Wasatch Plateau Area: Reflections Of Foreland To Intermontane Basin Transition, Geology of Eastern-Central Utah, Utah Geological Association Publication 19, pp 79.
Gillette, D.D. and M.G. Lockely, 1989. Dinosaur Tracks and Traces, Cambridge University Press, New York, N. Y. pp 442.
Hintze, L.F., 1982. Geologic History of Utah, BYU Geology Studies, Vol. 20, Pt. 3. pp 70 fig.46; p. 143, chart 25.
Lockley, M.G. and A.P. Hunt, 1995. Dinosaur Tracks, Columbia University Press, New York, NY. pp 1-30,192-212.
Parker, L.R. and R.L. Rowley, 1989. Dinosaur Footprints from a Coal Mine in East-Central Utah, Dinosaur Tracks and Traces, Cambridge University Press, New York, NY pp 362.
Ryer, T.A., 1991. Stratigraphy, Facies, And Depositional History of the Ferron Sandstone in the Canyon of Muddy Creek, East-Central Utah, Geology of Eastern-Central Utah, Utah Geological Association Publication 19, pp 45.
Thulborn, R.A., 1982. Speed and Gaits of Dinosaurs, Paleogeography, Palaeoclimatology, Palaeoecology, 38, 227-56.
Wade, M., 1989. The Stance of Dinosaur and the Cossack Dancer Syndrome. Dinosaur Tracks and Traces, Cambridge University Press, New York, N. Y. pp73.