REPRINT FROM
DINOSAUR TRACKS AND TRACES
Edited by DAVID D. GILLETTE AND MARTIN G. LOCKLEY
Cambridge University Press, 1989

(CONTINUED)


Tail drag structures are rare in mines, although linear depressions which are interpreted as such are seen (Robert L. Rowley pers. comm.). Two depressions, each about 8 cm deep, 2.5 m in length and 0.3 m wide, are present in a lightly bioturbated unit (Fig. 12). Both are curved. Their relation to one another suggests that they were produced at the same time by the same animal. Short lateral projections on the tail seem to have been present, making the parallel striations seen on the sides of these depressions. The infrequent occurrence of tail traces in these lakeshore muds suggests that the animals which lived here normally supported their tails above the surface.

Tracks which are different from the morphology of the rest of the footprints we have seen occur in one rock fall area (Fig. 13).They are on the recently exposed surface in Figure 8. A map has been prepared (Fig. 15), showing at least 50 of these specimens in an area 2 x 2.5 m. They were produced by a three-toed animal with a distinctly asymmetrical foot. One lateral toe is long and slender, almost 2.5 times the length of the median and opposite lateral toes. Total length from the heel to the end of the longest toe is 15 cm. No claw impressions are evident. Both left and right footprints occur. They apparently were produced by the pedes of a bipedal animal, since no footprints of any other shape or size are present. At least seven clusters of tracks occur where a single foot was being picked up, moved slightly and replaced. This shuffling gait, plus their random orientation, appears similar to tracks of extant birds as they feed on mud-dwelling organisms.Interestingly, associated with these tracks are many small 1 x 2 cm depressions and several thin (1.5 cm wide) elongate striations among the tracks, neither of which have been observed elsewhere in the lacustrine beds. Are these depressions beak or "peck" marks made in the mud by the animal as it fed?

Lockley (pers. comm. 1988) suggests that, because of the comparatively small size of these odd tracks, plus their widely separated toes, they probably are bird tracks. Currie (1981) studied several features of fossil and modern footprints, and pointed out that the angle of divergence of digits II and IV in small dinosaur tracks does not exceed 100°, while the same angle in bird tracks is greater. The angle in the Blackhawk specimens is 120°, well within that observed in birds.

Several techniques, inherent in the mining process, limit the observable roof area and in some cases destroy the specimens within the roof. The most common is white "rock dust", a powdered limestone, which is applied as a thick layer onto all freshly exposed mine surfaces in order to reduce the quantity of explosive coal dust. This completely covers all roof features or distorts observation of roof topography with a "snow-blindness" effect. Secondly, "top coal", a layer of coal usually from 10 to 50 cm thick, is left in place on the roof to cover certain types of roof shales which are otherwise subject to "air slacking" (the absorption and subsequent expansion of shales to the point that they fall from the roof). Because of these problems, only about 20% of the roof surface in any mine has been visible for study. But the most serious problem to the study of mine-roof paleontology is the recent development and use of long-wall retreat mining. The equipment in this technique removes coal in long 161 m swaths in such a way that the roof is unsupported and collapses within a few hours in the "gob area" behind the support shields. This completely destroys whatever features might have been preserved in the roof rock and makes studying the areas very hazardous.

Because dinosaur footprint casts are abundant in every level of swamp development which we can see underground, why don't they appear in outcrop? We have determined that they are indeed present and common in outcrop but are rarely recognized. For one thing, in lateral view they appear to be load castings which are expected (and present) in these sediments. Additionally, they weather rapidly, destroying characteristic toe and metatarsal features. In fresh exposures, however, and on protected undersurfaces of ledges there are often several intriguing three-lobed structures the same size and shape as those specimens in mine roofs (Fig. 14). We believe that many of these are dinosaur footprints, not load casts.

It is clear that the fluvial delta and coastal plain peat-forming environments of the Upper Cretaceous of the Rocky Mountain states had a large and varied dinosaur fauna recognized mainly from their tracks. Coal mines in the Blackhawk Formation of east-central Utah provide a unique opportunity to study their diversity, behavior and paleoecology.

Acknowledgments

We are grateful to Aureal T. Cross of Michigan State University for his infectious enthusiasm, help underground and insightful comments.

References

Bass, N. W., Eby, J. B., and Campbell, M. R. 1955. Geology and mineral fuels of parts of Routt and Moffat counties, Colorado. U.S. Geol. Surv. Bull.1027-D: 143-250.
Balsley, J. K., and Parker, L. R. 1983. Cretaceous Wave dominated Delta, Barrier Island, and Submarine Fan Depositional Systems: Book Cliffs east central Utah. Amer. Assoc. Petrol. Geol. Field Guide. 279 pp.
Currie, P. J. 1981. Bird footprints from the Gething Formation (Aptian Lower Cretaceous) of northeastern British Columbia, Canada. Jour. Vert. Paleont. 1(3-4):257-264.
Lockley, M. G. 1986. Dinosaur Tracksites. Univ. Colorado Denver Geol. Dept. Mag. Spec. Issue No. 1. 56 pp.
Lockley, M. G., Young, B. H., and Carpenter, K. 1983. Hadrosaur locomotion and herding behavior: evidence from footprints in the Mesaverde Formation, Grand Mesa Coal Field, Colorado. Mountain Geol. 20:5- 13.
Osterwald, F. W., and Dunrud, C. R. 1966. Instrumentation study of coal mine bumps, Sunnyside District, Utah. Utah Geol. Min. Surv. Bull. 80:97-110.
Parker, L. R. 1976. Paleoecology of the fluvial coal-forming swamps and associated floodplain environments in the Blackhawk Formation of central Utah. Brigham Young Univ. Geol. Studies 22:99-116.
1979. Paleoecology of delta and coastal plain plant communities in the Upper Cretaceous Blackhawk Formation of Utah. Botanical Soc. Amer. Misc. Ser. Publ. 157:35.
1980. Paleoecology of palm forests in Upper Cretaceous coal-forming swamps of central Utah. Botanical Soc. Amer. Misc. Ser. 158:86-87.
1981. Paleontology of the Cretaceous coal-forming environments in the Rock Springs Formation of Wyoming. Xlll Internat. Botanical Congr. Sydney AustraIia. Abst.:204.
Parker, L. R., and Balsley, J. K. 1977. Paleoecology of the coastal margin coal-forming swamps in the Upper Cretaceous Blackhawk Formation of central Utah. Geol. Soc. Amer. Abst.:1125-1126. Seattle.
Parker, L. R., and Rowley, L. R. 1989. Dinosaur Footprints from a Coal Mine in East-Central Utah. In D.D. Gillette and M.G. Lockley (ed) Dinosaur Tracks and Traces. (Cambridge University Press, 1989) pp. 360-366.in prep. Plant fossils and dinosaur footprints in coal mine roof surfaces.
Peterson, W. 1924. Dinosaur tracks in the roofs of coal mines. Nat. Hist. 24 (3):388-391.
Ratkevich, R. P. 1976. Dinosaurs of the Southwest. (Albuquerque: University of New Mexico Press) 115 pp.
Strevell, C. N. 1932. Dinosauropodes. (Salt Lake City: C. N. Strevell and Deseret News Press) 15 pp.
Wilson, W. D. 1969. Footprints in the sands of time. Gems and Minerals June 1969:25.

Editorial Note: The bird-like tracks illustrated in Figure 15 display morphologies consistent with the asymmetric foot of Hesperomis and its relatives.

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