TWO LATE TRIASSIC VERTEBRATE FAUNAS AT PETRIFIED FOREST NATIONAL PARK

Adrian P. Hunt

Department of Geology

University of Colorado at Denver

Denver, Colorado 80217

Spencer G. Lucas

New Mexico Museum of Natural History and Science

1801 Mountain Road N.W.

Albuquerque, New Mexico 87104

 

 

ABSTRACT

Two different vertebrate faunas are present in the Petrified Forest Formation (Upper Triassic) at Petrified Forest National Park, Arizona. The older fauna is Adamanian (late Tuvalian) in age, occurs in the Blue Mesa Member and is characterized by the presence of Rutiodon, Desmatosuchus and Stagonolepis. The younger fauna is Revueltian (Norian) in age, occurs in the Painted Desert Member and is characterized by the presence of Pseudopalatus and Typothorax. These faunas indicate that there was no major extinction at the Carnian\Norian boundary.

 

INTRODUCTION

Petrified Forest National Park (PEFO) has yielded a very large number of Late Triassic vertebrate fossils dating back to the excavations of Charles Camp in 1921 (Long et al., 1989). Since then, large collections have been amassed which are housed principally at the University of California Museum of Paleontology, Berkeley. Friedrich von Huene recognized in the 1920's the presence of two different faunas in the Upper Triassic of northeastern Arizona (note that Huene considered one fauna to be Middle Triassic in age), but Camp's (1930) influential revision of the phytosaurs only recognized one. Colbert and Gregory, (1957) similarly only recognized one fauna within the Triassic strata which are exposed at PEFO. However, Gregory (1957) resurrected Huene's concept of two faunas within the Chinle of the Colorado Plateau region (Table 1), which has been followed by all later workers. The aforementioned studies were hindered by the poor taxonomic state of the majority of the common families of Late Triassic vertebrates. Notably, the Carnian aetosaur Longosuchus and phytosaur Rutiodon were not distinguished from the Norian taxa Typothorax and Pseudopalatus respectively. However, in the last decade there have been complete or partial revisions of these groups, notably the metoposaurs (Hunt, 1993a, 1994; Hunt and Lucas, 1993b), phytosaurs (Ballew, 1989; Hunt, 1993b, 1994) and aetosaurs (Long and Ballew, 1985; Hunt and Lucas, 1991, 1992b). Utilizing these advances in taxonomy various authors have discussed the twofold division of PEFO vertebrate faunas but none have provided updated faunal lists at the species level (e.g., Long and Ballew, 1985; Long and Padian, 1986, Murry and Long, 1989; Parrish, 1989, 1993; Murry 1990; Hunt and Lucas, 1993b; Lucas, 1993). Lucas (1993) has recently published a revised stratigraphy of PEFO which allows the stratigraphic distribution of these faunas to be reevaluated. The purposes of this paper are threefold: (1) to provide updated faunal lists for both Late Triassic faunas at PEFO; (2) to evaluate their stratigraphic distribution and age; and (3) to comment briefly on the differences between the faunas. UCMP is the University of California Museum of Paleontology, Berkeley.

 

BLUE MESA LOCAL FAUNA

The older of the two vertebrate faunas from PEFO comes from the Blue Mesa Member of the Petrified Forest Formation, Chinle Group (Table 3). Most fossils from this unit come from the southern end of PEFO (south of Interstate 25) where the Blue Mesa Member has its main exposures within the park. This is the type fauna for the Adamanian land-vertebrate faunachron and is late Tuvalian (late Carnian) in age (Lucas and Hunt, 1993b). This fauna, like most late Carnian vertebrate faunas of Laurasia and northern Gondwanaland, is dominated by parasuchid reptiles (phytosaurs). Second most common in abundance are metoposaurid amphibians followed by aetosaurs. Other taxa together form a small minority of the fauna. The vast majority of specimens of this fauna come from a thin stratigraphic interval in the upper portion of the Blue Mesa Member (Lucas, 1993; Fig. 1).

PAINTED DESERT LOCAL FAUNA

The upper of the two vertebrate faunas at PEFO is from the Painted Desert Member of the Petrified Forest Formation. This unit is mainly exposed in the northern half of the park (north of Interstate 25), and this area has produced the majority of the Painted Desert local fauna. Some specimens come from the southern portion of the park in the Flattops area.

The Painted Desert fauna is Revueltian (Norian) in age on the basis of the presence of the phytosaur Pseudopalatus and the aetosaur Typothorax (Lucas and Hunt, 1993b). This fauna is also dominated by parasuchid specimens, but metoposaurs are rare and mainly restricted to localities dominated by terrestrial reptiles (Hunt and Lucas, 1993b; Hunt et al., 1993). Specimens of the aetosaur Typothorax are the second most abundant vertebrate fossils. Note that previous reports of a traversodontid from the Painted Desert Member (e.g., Murry and Long, 1989) are in error (Hunt and Lucas, 1993c). We identify the partial skeleton of a sphenosuchian (UCMP 129740), previously assigned to cf. Sphenosuchus sp. (Parrish, 1991), as cf. Hesperosuchus sp. and consider Padian's (1986) specimen of Coelophysis (UCMP 129618) to represent a new genus (Hunt and Santucci, 1993). Like the Adamanian fauna, the Revueltian fauna at PEFO is stratigraphically restricted and the majority of specimens occur in the lower part of the Painted Desert Member (Lucas, 1993; Fig. 1).

FAUNAL EVOLUTION ACROSS THE CARNIAN/NORIAN BOUNDARY

The Adamanian and Revueltian faunas at PEFO straddle the Carnian/Norian boundary, which has been postulated as a time of a major tetrapod extinction (e.g., Benton, 1994), but this has been disputed recently (Hunt and Lucas, 1992a; Lucas, 1994). Comparison between the two faunas at PEFO should provide a test of extinction theories. Even a cursory examination of Table 3 reveals that there is no major extinction at the Carnian/Norian boundary in the America Southwest, which is typified by the faunas at PEFO. The major groups of tetrapods (phytosaurs, aetosaurs, metoposaurs) exhibit generic level turnover at most. Terrestrial tetrapods appear more common in the Painted Desert fauna (Parrish, 1993), but this is biased by the fact that the older portion of the Revueltian is an acme zone for terrestrial tetrapods across the southwestern United States (Hunt and Lucas, 1993a). Aquatic/semiaquatic elements of the fauna (fish, metoposaurs), with the notable exception of phytosaurs, are less numerous in the Revueltian fauna (Hunt and Lucas, 1993a; Parrish, 1993). The only extinction at the Carnian/Norian boundary which has any global significance is the demise of the last dicynodont Placerias which disappears globally at this time though its disappearance precedes the end of the Carnian (Lucas and Hunt, 1993a). The replacement of xenacanth sharks by hybodonts at the Carnian/Norian boundary is consistent with a pattern throughout the Chinle Group (Huber et al., 1993). Some other rarer taxa may have become extinct at this time for example the enigmatic reptile Trilophosaurus. The apparent extinction of the prosauropods between the two faunas is an example of the Lazarus effect because these dinosaurs are known from Norian and Rhaetian (by footprints) portions of the Chinle Group elsewhere.

 

ACKNOWLEDGMENTS

We thank the Petrified Forest Museum Association for supporting various projects at PEFO and Vincent Santucci for diverse help.

 

REFERENCES

Ballew, K.L., 1989. A phylogenetic analysis of Phytosauria from the Late Triassic of the western United States; in Lucas, S.G. and Hunt, A.P., eds., Dawn of the age of dinosaurs in the American Southwest: Albuquerque, New Mexico Museum of Natural History, p. 340-348.

Benton, M.J., 1984. Late Triassic to Middle Jurassic extinctions among tetrapods: testing the pattern; in Fraser, N.C. and Sues, H.-D. (eds.), In the Shadow of Dinosaurs: Early Mesozoic Tetrapods: Cambridge, Cambridge University Press, in press.

Camp, C.L., 1930. A study of the phytosaurs with description of new material from western North America: University of California Monographs, v. 10, p. 1-175.

Colbert, E.H. and Gregory, J.T., 1957. Correlation of continental Triassic sediments by vertebrate fossils: Geological Society of America Bulletin, v. 68, p. 1456-1467.

Gregory, J.T., 1957. Significance of fossil vertebrates for correlation of Late Triassic continental deposits of North America: Report of the 20th Session of the International Geological Congress 1956, Section II, p. 7-25.

Huber, P., Lucas, S.G. and Hunt, A.P., 1993. Late Triassic fish assemblages of the North American Western Interior: Museum of Northern Arizona Bulletin, v. 59, p.51-66.

Hunt, A.P., 1993a. A revision of the Metoposauridae (Amphibia: Temnospondyli) of the Late Triassic with description of a new genus from the western North America: Museum of Northern Arizona Bulletin, v. 59, p. 67-97.

Hunt, A.P., 1993b. Taxonomy of phytosaurs (Reptilia: Archosauria) from the Blue Mesa Member of the Petrified Forest Formation, Petrified Forest National Park, northeastern Arizona: New Mexico Museum of Natural History and Science Bulletin, v. 3, p. G44-45.

Hunt, A. P., 1994. Vertebrate paleontology and biostratigraphy of the Bull Canyon Formation (Chinle Group, Upper Triassic), east-central New Mexico with revisions of the families Metoposauridae (Amphibia: Temnospondyli) and Parasuchidae (Reptilia: Archosauria)[Ph. D. dissertation]: Albuquerque, University of New Mexico, 403 p.

Hunt, A.P. and Lucas, S.G., 1991. Re-evaluation of "Typothorax" meadei, a Late Triassic aetosaur from the United States: Palaontologische Zeitschrift, v. 64, p. 317-328.

Hunt, A.P. and Lucas, S.G., 1992a. No tetrapod-extinction at the Carnian-Norian boundary (Late Triassic): evidence from the western United States and India: 29th International Geological Congress Abstracts, v. 1, p. 66.

Hunt, A.P. and Lucas, S.G., 1992b. The first occurrence of the aetosaur Paratypothorax andressi (Reptilia: Archosauria) in the western United States and its biochronological significance: Palaontologische Zeitschrift, v. 66, p. 147-157.

Hunt, A.P. and, Lucas, S.G., 1993a. Sequence stratigraphy and a tetrapod acme zone during the early Revueltian (Late Triassic\: early Norian) of western North America: New Mexico Museum of Natural History and Science Bulletin, v. 3, p. G46.

Hunt, A.P. and Lucas, S.G., 1993b. Taxonomy and stratigraphic distribution of Late Triassic metoposaurid amphibians from Petrified Forest National Park, Arizona: Journal of the Arizona-Nevada Academy of Sciences, v. 27, p. 89-96.

Hunt, A.P. and Lucas, S.G., 1993c. The search for advanced therapsids and mammals in Upper Triassic strata of Petrified Forest National Park: Petrified Forest National Park Research Abstracts, v. 2, p. 13.

Hunt, A.P. and Santucci, V.L. 1993. The record of Late Triassic dinosaurs at Petrified Forest National Park: Petrified Forest National Park Research Abstracts, v. 2, p. 14.

Hunt, A.P., Santucci, V.L. and Wall, W.P., 1993. Paleoecology of Late Triassic metoposaurid amphibians: evidence from Petrified Forest National Park: Park Science, v. 13, p.12.

Long, R.A., Lucas, S.G., Hunt, A.P. and McCrea, R., 1989. Charles Camp: collecting Late Triassic vertebrates in the American Southwest during the 1920's and 1930's; in Lucas, S.G. and Hunt, A.P., eds., Dawn of the age of dinosaurs in the American Southwest: Albuquerque, New Mexico Museum of Natural History, p. 65-71.

Long, R.A. and Ballew, K., 1985. Aetosaur dermal armor from the Late Triassic of southwestern North America, with special reference to material from the Chinle Formation of Petrified Forest National Park: Museum of Northern Arizona Bulletin, v. 54, p. 45-68.

Long, R.A. and Padian, K., 1986. Vertebrate biostratigraphy of the Late Triassic Chinle Formation, Petrified Forest National Park, Arizona: preliminary results; in Padian, K., ed., The beginning of the age of dinosaurs: faunal change across the Triassic-Jurassic boundary: Cambridge, University of Cambridge Press, p. 161-169.

Lucas, S.G., 1993. The Chinle Group: revised stratigraphy and chronology of Upper Triassic nonmarine strata in the western United States: Museum of Northern Arizona Bulletin, v. 59, p. 27-50.

Lucas, S.G., 1994. Triassic tetrapod extinctions and the compiled correlation effect; in Embry, A. F., ed., Pangaea: Canadian Association of Geologists Memoir, in press.

Lucas, S.G. and Hunt, A.P., 1993a. A dicynodont from the Upper Triassic of New Mexico and its biochronological significance: New Mexico Museum of Natural History and Science Bulletin, v. 3, p. 321-325.

Lucas, S.G. and Hunt, A.P., 1993b. Tetrapod biochronology of the Chinle Group (Upper Triassic), western United States: New Mexico Museum of Natural History and Science Bulletin, v. 3, p. 327-329.

Murry, P.A., 1989. Microvertebrate fossils from the Petrified Forest and Owl Rock members (Chinle Formation) in Petrified Forest National Park and vicinity, Arizona; in Lucas, S. G. and Hunt, A. P., eds., Dawn of the age of dinosaurs in the American Southwest: Albuquerque, New Mexico Museum of Natural History, p. 249-277.

Murry, P.A., 1990. Stratigraphy of the Upper Triassic Petrified Forest Member (Chinle Formation) in Petrified Forest National Park, Arizona, USA: Journal of Geology, v. 98, p. 780-789.

Murry, P.A. and Long, R.L., 1989. Geology and paleontology of the Chinle Formation, Petrified Forest National Park and vicinity, Arizona and a discussion of vertebrate fossils of the southwestern Upper Triassic; in Lucas, S. G. and Hunt, A.P., eds., Dawn of the age of dinosaurs in the American Southwest: Albuquerque, New Mexico Museum of Natural History, p. 29-64.

Padian, K., 1986. On the type material of Coelophysis Cope (saurischia: Theropoda) and a new specimen from the Petrified Forest of Arizona (Late Triassic: Chinle Formation); in Padian, K., ed., The beginning of the age of dinosaurs: faunal change across the Triassic-Jurassic boundary: Cambridge, Cambridge University Press. p. 45-60.

Parrish, J.M., 1991. A new specimen of an early crocodylomorph (cf.Sphenosuchus sp.) from the Upper Triassic Chinle Formation of Petrified Forest National Park, Arizona: Journal of Vertebrate Paleontology, v. 11, p. 198-212.

Santucci, V.L. and Hunt, A.P., 1993. Late Triassic vertebrate tracks discovered at Petrified Forest National Park: Park Science, v. 13, p. 14.

 

TABLE 1

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Lower portion of formation Upper portion of formation

Fish:

Ceratodus

Semionotus/Lepidotes

Amphibians:

Eupelor Rarer Eupelor

Phytosaurs:

Primitive species of Phytosaurus Primitive species of Phytosaurus

Advanced species of Phytosaurus

Aetosaurs:

Typothorax Rarer Typothorax

Desmatosuchus

Sphenosuchians:

Hesperosuchus

Mammal-like reptiles:

Placerias

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Table 1. Gregory's (1957) twofold division of the Chinle vertebrate faunas in the Petrified Forest Formation (sensu Lucas, 1993) in the region of what is now Petrified Forest National Park. Note that Hesperosuchus was found outside the park.

 

TABLE 2

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Blue Mesa Member local fauna Painted Desert Member local fauna

Sharks:

Xenacanthus moorei

Lissodus humblei

undescribed shark hybodont

Lungfish:

Arganodus dorotheae Arganodus dorotheae

Coelacanths:

indeterminate coelacanthid indeterminate coelacanthid

Other fish:

cf. Turseodus sp. cf. Turseodus sp.

indeterminate redfieldiid indeterminate redfieldiid

indeterminate colobodontid indeterminate colobodontid

Metoposaurid amphibians:

Buettneria perfecta Buettneria sp.

Apachesaurus sp. Apachesaurus gregorii

Primitive reptiles:

Trilophosaurus buettneria

undescribed ?proterochampsid

indeterminate sphenodontid

Phytosaurian reptiles:

Rutiodon carolinensis

Rutiodon crosbiensis

"Rutiodon" gregorii

Pseudopalatus pristinus

Pseudopalatus andersoni

Aetosaurian reptiles:

"Acaenasuchus geoffreyi"*

Stagonolepis wellesi

Desmatosuchus haplocerus

Paratypothorax andressi

Typothorax coccinarum

"Rauisuchian" reptiles:

Postosuchus kirkpatricki Postosuchus kirkpatricki

"Chatterjeea elegans"*

Sphenosuchian reptiles:

cf. Hesperosuchus sp.

Theropod dinosaurs:

"Chindesaurus bryansmalli"*

undescribed ceratosaurian

indeterminate theropod

Prosauropod dinosaurs:

indeterminate prosauropod?

Ornithischian dinosaurs:

Revueltosaurus callenderi

Mammal-like reptiles:

Placerias sp.

Vertebrate trace fossils:

coprolites coprolites

Rhynchosauroides sp.

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Table 2. Vertebrate faunas of Petrified Forest National Park (Long and Ballew, 1985; Murry, 1989, 1990; Murry and Long, 1989; Huber et al., 1993; Hunt, 1993a, b, 1994; Hunt and Lucas, 1993b; Lucas and Hunt, 1993b; Parrish, 1993; Santucci and Hunt, 1993; PEFO archives; original identifications). * indicates nomina nuda in Murry and Long (1989).

 

Figure 1. Stratigraphic distribution of the Blue Mesa and Painted Desert local faunas at Petrified Forest National Park, Arizona. FS is Flattops sandstone and PDS is Painted Desert sandstone.