AN IDENTIFICATION KEY TO PERMIAN TETRAPOD TRACKS FROM GRAND CANYON NATIONAL PARK

Adrian P. Hunt1 and Vincent L. Santucci2

1Mesalands Dinosaur Museum, Mesa Technical College, 911 South Tenth Street, Tucumcari, NM 88401
2Naitonal Park Service, PO Box 592, Kemmerer, WY 83101


Abstract—Abundant Permian vertebrate tracks from Grand Canyon National Park are preserved in the Coconino Sandstone and Hermit Shale. Most of these tracks were studied and described by Charles Gilmore of the Smithsonian Institution during the 1920s. A recent renaissance in the study of Permian tetrapod ichnofaunas in North America has resulted in a reevaluation of their ichnotaxonomy. A key to the identification of the Permian tracks from Grand Canyon has been developed utilizing the revised nomenclature.

Introduction

The most significant early collections of Permian tracks to be described from North America came from Grand Canyon National Park. Charles Gilmore of the Smithsonian Institution described most of these footprints in a series of classic monographs (Gilmore, 1926, 1927, 1928). During the last five years there has been a renaissance of the study of Permian tracks that has led to a new understanding of the significance of the Grand Canyon specimens (e. g., Haubold, 1996). These studies have led to a reevaluation of the correct nomenclature for these tracks and of their true diversity (Hunt and Santucci, 1998). The purpose of this paper is to provide a brief identification key to the Permian tracks from the Grand Canyon utilizing the revised nomenclature. Lucas and Hunt (1998) provide a complimentary key to identifying some Permian tracks from New Mexico. Note that this key is only for Permian tracks (Coconino Sandstone and Hermit Shale) and should not be used for tracks from the Supai Group.

Hunt and Santucci (1998) recognize the following Permian footprint types from the Grand Canyon:

• Coconino Sandstone_Chelichnus bucklandi,Chelichnus gigas,Chelichnus duncani;

• Hermit Shale_Batrachichnus delicatulus, Parabaropus coloradensis, Hyloidichnus bifurcatus, Gilmoreichnus hermitanus, Limnopus sp., Ichniotherium sp.

Identification Key



Figure 1—Types of animal footprints from the Permian of the Grand Canyon National Park. A, Batrachichnus delicatulus. B, Limnopus sp. C, Ichniotherium sp. D, Chelichnus spp. E, Parabaropus coloradensis. F, Gilmoreichnus hermitanus. G, Hyloidichnus bifurcatus. Scale bars are 1 cm. The two scale bars in D indicate the size range of this ichnogenus.
pelycosaurian reptile]

1. Four-toe impressions on hand print.

Yes - Go to 2.

No - Go to 3.

[Note that unusual preservation conditions may result in the preservation of less than the actual number of digit impressions. Be particularly wary of tracks that appear indistinct. If your specimen is from the Coconino and only has four apparent toe impressions you are probably dealing with a poorly preserved specimen of Chelichnus - see no. 4]

2. Foot print is less than 5 cm long.

Yes - Batrachichnus delicatulus (Figure 1A)

[This is the most common small track in the Hermit Shale and is widespread in redbeds of Permian age
throughout the world and represents a small amphibian]

No - Limnopus sp. (Figure 1B)

[This is track is only known from one example from the Hermit Shale - see Hunt and Santucci (1998) and represents a larger amphibian]

3. Hand and foot prints are about the same size and have short toe impressions.

Yes - Go to 4

No - Go to 5

4. Foot print has a length of (Figure 1D).

1-1.5 cm - Chelichnus bucklandi

2.5-7.5 cm - Chelichnus duncani

7.5-150 cm - Chelichnus gigas

[These are the only three track species that you should find in the Coconino Sandstone. If you found these tracks in the Hermit Shale then you have probably made a mistake. Chelichnus tracks are locally very common in the Coconino and they display a tremendous range of preservational variants that can give very different looking footprints. These tracks may represent a herbivorous caseid reptile]

5. Foot print is greater than 50 cm long with wide toe impressions.

Yes - Go to 6

No - Go to 7

6. Footprints are placed almost in front of each other (narrow trackway) and the footprint has a very long heel impression relative to the hand.

Yes - Parabaropus coloradensis (Figure 1E)

[This is one of the largest tracks in the Hermit Shale and probably represents a primitive tetrapod such as a seymouriamorph or a diadectid]

No - Ichniotherium sp. (Figure 1C)

[This is a very rare Hermit Shale fossil, very common in Europe, that probably represents an edaphosaurian reptile]

7. Foot length is less than 50 cm with narrow toe impressions. Well developed heels and curved digit impressions.

Yes - Gilmoreichnus hermitanus (Figure 1F)

[This is most easily confused with Hyloidichnus bifurcatus. This track was made by a small

No - Hyloidichnus bifurcatus (Figure 1G)

[Some specimens have split tips to their toe impressions which is the result of a primitive way of walking, not toes that actually divide into two parts. This type of track was made by a seymouriamorph or a diadectid]

References

Gilmore, C. W. 1926. Fossil footprints from the Grand Canyon: Smithsonian Miscellaneous Collections, v. 77(9), 41 p.

———. 1927. Fossil footprints from the Grand Canyon: second contribution: Smithsonian Miscellaneous Collections, v. 80(3), 78 p.

———. 1928a. Fossil footprints from the Grand Canyon: third contribution: Smithsonian Miscellaneous Collections, v. 80(8), 16 p.

Haubold, H. 1996. Ichnotaxonomie und Klassifikation von Tetrapodenfaehrten aus dem Perm: Hallesches Jahrbuch Geowissenschaften, v. B18, p. 23-88.

Hunt, A. P., and V. L. Santucci. 1998. Taxonomy and ichnofacies of Permian tetrapod tracks from Grand Canyon National Park, Arizona: this volume.

Lucas, S. G. and A. P. Hunt. 1998. An identification key for Early Permian tetrapod tracks from the Robledo Mountains, southern New Mexico: New Mexico Geological Society, in press.