TAXONOMY AND ICHNOFACIES OF PERMIAN TETRAPOD TRACKS FROM GRAND CANYON NATIONAL PARK, ARIZONA

Adrian P. Hunt1 and Vincent L. Santucci2

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


Abstract—A recent renaissance in the study of Permian tetrapod ichnofaunas has resulted in a reevaluation of the important specimens from Grand Canyon National Park. The ichnofauna of the Coconino Sandstone consists of Chelichnus bucklandi, C. gigas and C. duncani and represents the cosmopolitan Chelichnus ichnofacies. The ichnofauna of the Hermit Shale includes Batrachichnus delicatulus, Parabaropus coloradensis, Hyloidichnus bifurcatus, Gilmoreichnus hermitanus, Limnopus sp. and Ichniotherium sp. and represents an "inland" redbed facies.

Introduction

Undoubtedly the most significant collection of Paleozoic vertebrate tracks in North America was collected and described by Charles Gilmore of the United States National Museum (Smithsonian) in a series of classic works (Gilmore, 1926b, 1927b, 1928a). Gilmore collected these specimens from three formations in Grand Canyon National Park. During the last five years there has been a radical reappraisal of Permian tetrapod tracks and ichnofacies.The purpose of this paper is to briefly review the taxonomy of the Grand Canyon collections of tetrapod tracks and to comment on their ichnofacies significance in the light of these recent changes.

Ichnotaxonomy

History of study.—Schuchert (1918) first collected tetrapod tracks in Paleozoic strata on the South Rim of the Grand Canyon. Lull (1918) utilized this collection from the Permian Coconino Sandstone in the first scientific description of Paleozoic tetrapod tracks from Arizona. In 1924 the National Park Service invited Charles Gilmore to visit Schuchert's locality and to prepare an in situ exhibit on the now abandoned Hermit Trail (Spamer, 1984). Gilmore (1926b) described this new Coconino collection and was later funded by the Marsh Fund Committee of the National Academy of Sciences (1926) and the Grand Canyon Exhibit Committee of the National Academy of Sciences (1927) to make additional collections and exhibits (Spamer, 1984). These new collections came from the Hermit Shale (Permian) and Wescogame Formation of the Supai Group (Pennsylvanian) as well as the Coconino
and were described by Gilmore in additional monographs (Gilmore, 1927b, 1928a) and a short paper on the first tracks from the North Rim (Gilmore and Sturdevant, 1928). Gilmore also wrote three more popular papers describing his collecting efforts (Gilmore, 1926a, 1927a, 1928b).

For the next 70 years there was little reevaluation of Gilmore's work except by Don Baird of Princeton (Baird, 1952, Baird in Spamer, 1984). A renaissance of Paleozoic track studies took place in the mid 1990's. The Rosetta Stone for a new reevualtion of Permian tracks was provided by studies of the extensive ichnofaunas from the redbeds of southern New Mexico (Haubold et al., 1995, Hunt et al., 1995). The New Mexico tracksites provided large sample sizes of all the most significant Permian ichnotaxa and included a broad range of preservational variants. These samples provided a new perspective on the plethora of ichnotaxonomic names of tetrapod tracks from Permian redbeds, most of which had been described on the basis of small sample sizes. During the same timeframe there was a major reevaluation of the equally confused ichnotaxonomy of tetrapod tracks from Permian eolianites (Morales and Haubold, Morales, 1995; Haubold et al., 1995; McKeever and Haubold, 1996). Haubold (1996) reviewed the new ichnotaxonomy of Permian tracks that derived from these works. One of the main purposes of this work is to provide a new evaluation of the taxonomy of the Permian tetrapod tracks from the Grand Canyon (Tables 1-2).

Coconino Sandstone.—The first fossil footprints to be described came from Permian eolianites of Scotland (Grierson, 1828). Subsequently, important ichnofaunas were described differences in footprint morphology or trackway pattern reflected the presence of different trackmakers. A reevaluation of the tetrapod ichnotaxa from the Hermit Shale of the Grand Canyon reveals a lower ichnodiversity than was previously recognized (Table 2).


Table 1—Revised ichnotaxonomy of tetrapod ichnofauna of the Coconino Sandstone at Grand Canyon National Park (McKeever and Haubold, 1996).
Chelichnus duncani (Owen, 1842) (= Baropezia arizonae, Allopus? arizonae, Baropezia eakini, Agostopus matheri, Agostopus medius, Palaeopus regularis, Barypodus tridactylus, Barypodus metszeri, Nanopus maximus, Laoporus noblei in part of Gilmore, 1926b)
Chelichnus gigas Jardine, 1850 (=Barypodus palmatus, Amblyopus pachypodus, Baropus coconinoensis)
Chelichnus bucklandi (Jardine, 1850) (=Dolichopodus tetradactylus, Laoporus schucherti, Laoporus coloradensis, Nanopus merriami, Laoporus noblei of Lull, 1918)


Table 2—Revised ichnotaxonomy of tetrapod ichnofauna of the Hermit Shale at Grand Canyon National Park (Haubold et al., 1995a; this paper).
Batrachichnus delicatulus (Lull, 1918) (= Exocampe (?) delicatula, Batrachichnus delicatula, Batrachichnus obscurus, Dromillopus parvus)
Parabaropus coloradensis (Lull, 1918)(= Megapezia (?) coloradensis)
Hyloidichnus bifurcatus Gilmore, 1927b (= Hyloidichnus whitei)
Gilmoreichnus hermitanus (Gilmore, 1927b)(= Palaeosauropus hermitanus, Hylopus hermitanus, Collettosaurus pentadactylus, Cursipes sp.)
Limnopus sp. (= Parabaropus coloradensis of Gilmore, 1927b in part)
Ichniotherium sp. (= Parabaropus coloradensis of Gilmore 1928a in part)

The Hermit Shale ichnofauna includes the nearly ubiquitous temnospondyl track Batrachichnus delicatulus. Reptile tracks include Parabaropus coloradensis and Hyloidichnus bifurcatus (seymouriamorph or diadectid tracks) and the small pelycosaur track Gilmoreichnus hermitanus. Two other more problematical ichnotaxa are present in the Hermit Shale collections. Haubold (1971) named Ichniotherium gilmorei for a specimen (USNM 11707) originally described by Gilmore (1928a, pl. 1). Unfortunately the holotype of this specimen is now lost (Haubold et al., 1995a). Ichniotherium is common in Europe but very rare in North America (Haubold et al., 1995a; Hunt et al., 1995; Hunt and Lucas, 1998b). A second problematic specimen is USNM 11598, a specimen that Gilmore (1927b, pl. 17, no. 1; Haubold et al., 1995a, fig. 24B) assigned to Parabaropus coloradensis. Haubold et al. (1995a) noted that this specimen is different from P. coloradensis in possesing distinct plantigrade impressions, elongate pedal imprints and less diverging digit impressions. They concluded that this trackway represents undertracks of either a Dimetropus specimen that preserves prominent pads and reduced digit impressions or a large Limnopus specimen (e. g., Limnopus zeilleri). We prefer the second interpretation because of the large manual pad impressions and because the long axis of the manual imprints is inclined at a high angle to the direction of travel.

Ichnofacies

History of study.—Gilmore was aware that the Coconino Sandstone and Hermit Shale were deposited in different sedimentary environments but Baird (1965) was the first to emphasize that the differences between the Permian ichnofaunas of the redbeds of the American West and those of eolianites might be a result of facies differences. There has been a long tradition of recognizing ichnofacies in invertebrate traces, but the concept has only recently been applied to vertebrate tracks (Lockley et al., 1994). Tetrapod ichnofacies have been defined as "multiple ichnocoenoses that are similar in ichnotaxonomic composition and show recurrent association in particular environments (Lockley et al., 1994, p. 242). Lockley et al. (1994), Hunt et al. (1995), Haubold (1996) and Hunt and Lucas (1998a) have all discussed Permian tetrapod ichnofacies.

by eolian strata of Germany (Cornberger Sandstein), Colorado (Lyons Sandstone) and Arizona (Coconino Sandstone, DeChelly Sandstone) as well as additional specimens from Scotland (Hopeman, Corncockle and Locharbriggs Sandstone Formations). A large literature described many ichnotaxa from these formations. However, recent work spearheaded by Hartmut Haubold has demonstrated that virtually all tetrapod tracks from Permian eolinaites represent three species of one genus, with only the rarest exceptions (Haubold et al., 1995b; McKeever and Haubold, 1996; Haubold, 1996). Certainly all the Coconino tracks fall within three species of Chelichnus (McKeever and Haubold, 1996). Chelichnus is characterized by rounded manual and pedal impressions that are of nearly equal size and which exhibit five short, rounded toe impressions (though less than five may be preserved). Trackways have a pace angulation of about 90o and the manual and pedal impressions are close together (McKeever and Haubold, 1996). The three valid species of Chelichnus are distinguished on the basis of size alone and are presumed to be the tracks of caseid-like animal (e. g. Haubold, 1971). Chelichnus bucklandi has pedal impression lengths of 10-25 mm, C. duncani of 25-75 mm and C. gigas of 75-125 mm (McKeever and Haubold, 1996). Thus, all Gilmore's (and Lull's) named ichnotaxa from the Coconino Sandstone of the Grand Canyon can be placed in one of these three species. Gilmore (1927b) was aware of the similarity of some of his specimens from the Grand Canyon to those from Scotland, but he persisted with his (and Lull's) distinct ichnotaxonomy (e. g., Gilmore, 1928a).

Size by itself is not the ideal criterion to distinguish between ichnospecies, but, the revised ichnotaxonomy presented here represent the current consensus. The low ichnotaxonomic diversity in Table 1 is in keeping with the low animal diversity that would be expected in a dunefield.

Hermit Shale.—The Hermit Shale tetrapod tracks occur in redbeds, in contrast to the eolian strata of the Coconino Sandstone. Recent work has indicated that Permian redbed ichnofaunas are of low diversity and cosmopolitan nature (Haubold et al., 1995a; Haubold, 1996; Hunt and Lucas, 1988b). A reevaluation of Gilmore's ichnotaxonomy indicates that he had overestimated the diversity of the Hermit Shale ichnofauna. Gilmore, in common with all pre-1990's ichnologists, was not sufficiently aware of the variable traces that could made by a single trackmaker given variations in substrate conditions and gait. Thus, Gilmore assumed that all Coconino Sandstone.—The low-diversity tetrapod ichnofauna of the Coconono Sandstone clearly represents the Chelichnus ichnofacies (= Laoporus ichnofacies of Lockley et al., 1994) that is known from the DeChelly and Coconino Sandstone of Arizona, the Lyons Sandstone of Colorado, the Hopeman, Corncockle and Locharbriggs Sandstone Formations of Scotland, the Cornberger Sandstein of Germany and the Los Reyunos Formation of Argentina (Hunt and Lucas, 1988a,b).

Hermit Shale.—Permian tetrapod ichnofaunas from redbeds are cosmopolitan in nature, but a number of ichnofacies can be recognized (Hunt et al., 1995; Hunt and Lucas, 1988a). Hunt and coworkers (Hunt et al., 1995; Hunt and Lucas, 1988a) have suggested that the Hermit Shale ichnofauna shows similiarities with track assemblages from "inland" environments that were not in close proximity to a marine shoreline. This hypothesis is supported by the following featrures of the Hermit Shale ichnofauna (Hunt et al., 1995; Hunt and Lucas, 1988a):

• Presence of Ichniotherium and Parabaropus that are "inland" facies fossils;

• Absence of Dromopus that is abundant in coastal ichnofaunas;

• Presence of Limnopus that is uncommon in coastal ichnofaunas.

The Hermit Shale ichnofauna shows several similarities with the "inland" ichnofauna of the Sangre de Cristo Formation in New Mexico (Ichniotherium, Parabaropus), but is distinct in lacking Dromopus and Dimetropus.

Conclusions

Recent work has resulted in a major reevaluation of the ichnotaxonomy and ichnofacies context of the Permian tetrapod tracks of the Grand Canyon. Hopefully this renaissance of knowledge about Paleozoic tracks will spur further study of the important ichnofaunas of Grand Canyon National Park.

References

Baird, D. 1952. Revision of the Pennsylvanian and Permian footprints Limnopus, Allopus and Baropus: Journal of Paleontology, v. 26, p. 832-840.

———. 1965. Footprints from the Cutler Formation: United States Geological Survey Professional Paper 503C, p. C47-C50.

Gilmore, C. W. 1926a. Collecting fossil footprints in Arizona: Smithsonian Miscellaneous Collections, v. 78(1), 20-23.

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

———. 1927a. Collecting fossil footprints in the Grand Canyon, Arizona: Smithsonian Miscellaneous Collections, v. 78(7), 45-48 p.

———. 1927b. 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.

———. 1928b. Fossil footprints in the Grand Canyon of the Colorado, Arizona: Smithsonian Institution Publication, v. 2957, p. 7-10.

———, and G. E. Sturdevant. 1928. Discovery of fossil tracks on the north rim of the Grand Canyon: Science, v. 67, p. 216.

Grierson, J. 1828. On footsteps before the flood, in a specimen of red sandstone: Edinburgh Journal of Science, v. 8, p. 130-134.

Haubold, H. 1971. Ichnia amphibiorum et reptiliorum fossilium: Handbuch der Paleoherpetologie, Teil 18: Stuttgart, Gustav Fischer Verlag, 124 p.

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

———, A. P. Hunt, S. G. Lucas, and M. G. Lockley. 1995a. Wolfcampian (Early Permian) vertebrate tracks from Arizona and New Mexico: New Mexico Museum of Natural History and Science Bulletin, v. 6, p. 135-165.

———, M. G. Lockley, A. P. Hunt, and S. G. Lucas. 1995b. Lacertoid footprints from Permian dune sandstones, Cornberg and DeChelly sandstones: New Mexico Museum of Natural History and Science Bulletin, v. 6, p. 235-244.

Hunt, A. P., and S. G. Lucas. 1998a. Implications of the cosmopolitansim of Permian tetrapod ichnofaunas: New Mexico Museum of Natural History and Science Bulletin, in press.

———, and ———. 1988a. Vertebrate ichnofaunas of New Mexico and their bearing on Early Permian tetrapod ichnofacies:New Mexico Museum of Natural History and Science Bulletin, in press.

———, M. G. Lockley, H. Haubold, and S. Braddy. 1995. Tetrapod ichnofacies in Early Permian red beds of the American Southwest: New Mexico Museum of Natural History and Science Bulletin, v. 6, p. 295-301.

Lockley, M. G., A. P. Hunt, and C. Meyer. 1994. Vertebrate tracks and the ichnofacies concept: implications for paleoecology and palichnostratigraphy; in Donovan, S., ed., The paleobiology of trace fossils: London, John Wiley, p. 241268.

Lull, R. S. 1918. Fossil footprints from the Grand Canyon of the Colorado: American Journal of Science, fourth series, v. 45, p. 337-346.

McKeever, P. J. and H. Haubold. 1996. Reclassification of vertebrate trackways from the Permian of Scotland and related forms from Arizona and Germany: Journal of Paleontology, v. 70, p. 1011-1022.

Morales, M. and H. Haubold. 1995. Tetrapod tracks from the Lower Permian DeChelly Sandstone of Arizona: systematic description: New Mexico Museum of Natural History and Science Bulletin, v. 6, p. 251-261.

Scuchert, C. 1918. On the Carboniferous of the Grand Canyon of Arizona: American Journal of Science, fourth series, v. 45, p. 362-369.

Spamer, E. E. 1984. Paleontology in the Grand Canyon of Arizona: 125 years of lessons and enigmas from the late Precambrian to the present: The Mosasaur, v. 2, p. 45-128.