Upper triassic chinle formation, petrified forest national park, arizona stephen t. Hasiotis




Дата канвертавання17.04.2016
Памер34.74 Kb.
PROBABLE REPTILE NESTS FROM THE

UPPER TRIASSIC CHINLE FORMATION,

PETRIFIED FOREST NATIONAL PARK, ARIZONA
STEPHEN T. HASIOTIS1 and ANTHONY J. MARTIN2

1Department of Geological Sciences, Campus Box 399, University of Colorado, Boulder, CO 80309-0399

2Geosciences Program, Emory University, Atlanta, GA 30322
____________________

Abstract—We report evidence for the earliest known reptilian nests in alluvial deposits from the Petrified Forest Member of the Upper Triassic Chinle Formation (Early Norian), Petrified Forest National Park, Arizona. The Triassic nest ichnofossils are nearly 120 million years older than nests previously described from the Late Cretaceous of the Western Interior of the United States. These structures are found in the first "flattop sandstone #1" above the Sonsela Sandstone/Rainbow Forest Sandstone complex at the south end of the park. The hollow, bowl-shaped pits are present in relatively large numbers and occur in two small areas. The pit openings are sometimes constricted with an expansion below. Inside, the shape is circular to elliptical and forms spherical to elongate pits. Rarely, scratch marks are found across the walls. Internal, partial layering is found at the bottom and along the sides. Some pits are rimmed by elliptical depressions with irregular surfaces that contain a few poorly defined vertebrate footprints.

The bowl-shaped pits are interpreted as nest-holes constructed by vertebrates, possibly phytosaurs, aetosaurs, rauisuchians, or dinosaurs. The nests are very similar to those constructed by Late Cretaceous dinosaurs and sea turtles, extant turtles (Reptilia: Cheloniidae), crocodiles, and alligators (Repitilia: Crocodylidae). Females that congregated in specific areas, which are interpreted as nesting sites, most likely excavated the Chinle nests. The patches of irregular ground around the nests represent trample ground and body pits created by the adult. The layering within the nests may represent active modification of the internal walls and floors and backfilling after eggs were deposited. Possible impressions in the basal portion may represent unhatched or partial eggshells.

These ichnofossils appear to represent the earliest known evidence of vertebrate reproductive behavior. If so, they would also represent one of the earliest forms of parental care such that eggs were placed in specialized structures. This is a major step toward the rearing of offspring. Nesting has likely evolved several times in different groups of primitive vertebrates, but basic nest-hole architecture in extant reptiles with Early Mesozoic ancestry has changed very little in nearly 220 million years.

____________________


INTRODUCTION
The fossil record of amniotes begins in the Pennsylvanian Period based on reptilian body fossils and footprints (Carroll, 1964, 1969; Lockley, 1989). Body and trace fossil evidence for reptilian nesting behavior is exceedingly rare in the geologic record. Late Cretaceous ground-nest excavations of non-avian dinosaurs (Horner and Makela, 1979; Horner, 1992; Novell et al., 1995; Varrichio et al., 1997) and sea turtle nests (Bishop et al., 1997) represent in situ evidence of nesting. Fossil eggshell fragments, complete egg clutches, and groups of juvenile remains also provide evidence of nesting (Andrews, 1932; Lapparent and Zybyszewski, 1957; Hirsch et al., 1989; Hirsch, 1994; Kirkland, 1994).

Possible Late Triassic dinosaur eggs (Kitching, 1979; Grine and Kitching, 1987) and Permian eggshell (Hirsch, 1979) have also been reported, but not in nests. Smith (1987) documented the helical burrows of mammal-like reptiles in Upper Permian rocks of South Africa, but made no inferences to brood rearing. No specialized nest structures have been reported from rocks older than the Cretaceous.

We report on evidence for the earliest known reptile nests from the Upper Triassic Chinle Formation, Petrified Forest National Park, Arizona (Fig. 1). Hollow, bowl-shaped pits present in large numbers within limited areas exhibit pronounced similarities to hole-nests excavated by extant turtles (Reptilia: Cheloniidae), crocodiles, and alligators (Repitilia: Crocodylidae). Although no fossil material was found within the nests, the size and location of the nests suggests that the constructors may have been reptiles such as aetosaurs, phytosaurs, rauisuchians, or dinosaurs.

Figure 1—Locality map of Petrified Forest National Park (PEFO), Arizona, and the ichnofossil study area (X).



GEOLOGIC SETTING

The study area is at the south end of Petrified Forest National Park (PEFO), Arizona (Fig. 1), where the lower part of the Upper Triassic Chinle Formation is exposed in badlands, buttes, and mesas (Fig. 2). The lower part of the Chinle was deposited in a succession of valley-fill sequences (Cooley, 1958, 1959; Repenning et al., 1969; Stewart et al, 1972; Demko, 1995; Demko et al. 1998). The upper part of the Chinle, of which only the lower part of the Owl Rock Member is preserved within park boundaries, was deposited in a regionally dynamic basin complex of alluvial-lacustrine systems (Stewart et al, 1972; Dubiel, 1989, 1994).


Figure 2—Composite measured section of the Upper Triassic Chinle Formation in Petrified Forest National Park, the stratigraphic position of the ichnofossils (asterisk), and relationship of these units to the regional geology. Modified from Dubiel et al. (this volume).

Bowl-shaped pits are present locally in the flattop sandstone #1 (Billingsley 1985) above the Sonsela/Rainbow Forest Sandstone complex in the upper part of the Petrified Forest Member in the Chinle Formation (Norian) (Fig. 2). These ichnofossils are found in the uppermost part of a 1.5-m-thick upper fine- to medium-grained, trough cross-stratified sandstone. At this locality, the unit has a relatively planar base and a slightly undulatory top representative of an exposure surface with pedogenic features. Further north, this unit contains inclined, heterolithic, accreted strata composed of trough cross-bedded and ripple-bedded sandstones interbedded with mudstone and siltstone. Also in this interval are small, silicified trunks with lateral roots, rhizoliths, small-diameter backfilled meniscate burrows, crayfish crawling trails, wasp cocoons, coleopteran or lepidopteran cocoons, and termite nests assigned to Archeoentomichnus isp.

The ichnofossil-bearing rocks are interpreted as deposits from medium- to high-sinuosity meandering river. The floodplain contained immature cumulative paleosols capped by a simple, mature paleosol. Based on the sedimentary structures and the degree of pedogenesis, the bowl-shaped pits are interpreted to have been in areas close to the active channel where paleosols were weakly developed.


DESCRIPTION OF THE ICHNOFOSSILS

Two distinct localities with a combined total of over 100 pits are found along first flattops sandstone #1 (sensu Billingsley, 1985). Many of the pits at the first locality occur in large float blocks weathered from the outcrop. The pits at the second locality are found in situ along the top of the outcrop. The density of pits is approximately 1/m2 based on measurements for blocks with more than one pit. Proximity of pits averaged 64 +/- 38 cm (N=19), although at least one pair of pits show overlap and another pair had a distance of 150 cm between them.

Discrete hollow, bowl-shaped pits characterize over 100 ichnofossils (Fig. 3). The circular to elliptical openings range from 10-20 cm in diameter and average between 15-16 cm. Occasionally they are associated with a constriction at or just below the paleosurface. Below the opening the internal part of the structures range from 11-44 cm in diameter, averaging 30-35 cm. The walls and floors appear compacted with several layers of sediment. Narrow, elongate, shallow furrows, 7-15 cm in length, are rare and preserved in the walls. The bottoms of a few of the structures contain crescentic to oval indentations around 4-5 cm long and 2-4 cm wide. In some cases, shallow, broad depressions from 63-65 cm long and 35-40 cm wide are present above the deeper, larger pits. The surfaces of these depressions are highly irregular with bumpy protrusions and multidirectional elongate furrows found clustered with one another (Fig. 4). Rare individual vertebrate tracks are found with the irregular surfaces.

INTERPRETATION

The pits and depressions are interpreted as vertebrate nest-holes based on our comparisons of the Triassic ichnofossils to modern burrows and nests constructed by invertebrates and vertebrates. The pits represent the nest proper, most likely excavated by females, in which the eggs were laid. These ichnofossils are very similar to the nest-holes excavated by extant sea and terrestrial turtles (Reptilia: Cheloniidae), crocodiles, and alligators (Repitilia: Crocodylidae) (Brannen and Bishop, 1993; Bishop et al., 1997). In the Triassic nests, the elongate furrows and the compacted thin layers of sediment along the walls and floors reflect the excavation and completion of the nest prior to egg-laying. The crescentic to oval patterns seen in one of the nests grossly resemble impressions of eggshells or eggs. Modern turtle and crocodile eggs have a leathery texture and are not highly calcified. Egg characteristics cannot be determined from the Triassic impressions at this time. The large shallow depressions associated with some of the nests are interpreted as body pits made by the female excavating her nest and laying her eggs. The highly irregular bumpy protrusions and multidirectional elongate furrows within these shallow depressions represent trampled ground that sometimes preserve partial footprints of the nest-maker. Smaller, incomplete pits associated with the nests are interpreted as test pits made by females testing the substrate conditions (e.g., texture, consistency, moisture), as observed in extant turtles (Hailman and Elowson, 1992; Brannen and Bishop, 1993). Thus, several incomplete or much smaller pits adjacent to completed pits and other pits and depressions show various stages of completion as compared to those that appear to be completely constructed nests.




Figure 3 —An example of a block of sandstone with the nest ichnofossils, with a schematic diagram of the block.

Figure 4 — A. Example of trampled ground around some of the nest ichnofossils. B. Close-up of a partial footprint within the trampled area.
The distribution of the Chinle nest-holes are also similar to the nest distribution of extant sea and terrestrial turtles (Reptilia: Cheloniidae), hole-nesting crocodiles, and hole-nesting alligators (Repitilia: Crocodylidae), as opposed to mound-nesters (Cott, 1961; Webb et al., 1983; Woodward et al., 1984; Thorbjarnarson, 1996). Today, the females of these reptiles congregate along rivers, swamps, and beaches to construct their nests and lay their eggs. The females and their offspring return to the same areas to nest for many consecutive years, reflecting nesting site-fidelity (Cott, 1961; Carr, 1967; Mazzotti, 1989; Leslie, 1997). Similar patterns of nest site-fidelity have also been observed with nests constructed by Late Cretaceous dinosaurs (Horner, 1982). Nests interpreted as having been constructed during the same reproductive season are separated by a mean distance analogous to the body-length of adult hadrosaurs. For the Chinle, the spacing between the nests is similar to the length of the interpreted body pits. A few examples of nest construction overlap likely reflect recolonization of the nesting site. This interpretation is supported by observed nest-site reuse by extant crocodilians and alligatorids (Cott, 1961; Webb et al., 1983; Thorbjarnson and Hernandez, 1993). However, in some cases, nesting sites can be also occupied by more than one species of reptile, such as crocodilians and iguanas (Dugan et al., 1981; Bock and Rand, 1989). This implies that the nests may not necessarily be indicative of monospecific nest makers. At this point, the morphology of the Chinle nests suggests only one type of nest-maker.


DISCUSSION

Based on the size, spacing, and distribution of the nest ichnofossils, the constructors could have been aetosaurs, small phytosaurs, rauisuchians, or dinosaurs. Within 1500 m of the nesting sites is fossil evidence of reptilians that lived within the same stratigraphic interval, which include a partial skull, teeth, and armor plates of phytosaurs, armor plates of aetosaurs, and tracks and trackways of swimming reptiles (Martin and Hasiotis, 1998). Evidence of theropod dinosaurs are also found in both the lower and higher stratigraphic levels (Padian, 1986; Hunt, 1995; Long and Murray, 1995; Hunt et al., 1996; Martin and Hasiotis, 1998). The Triassic nest ichnofossils are nearly 120 million years older than nests previously described from the Late Cretaceous of the Western Interior of the United States. Whoever the nest-makers were, their ichnofossils suggest that they were gregarious, lived and bred along or in perennial watercourses, and exhibited basic parental instincts. There is no way to tell if these reptiles tended to their nests, eggs, or young after hatching. However, the pattern of nests is analogous to that observed for dinosaurs in the Late Cretaceous purported to have cared for their eggs/offspring (Horner and Makela, 1979; Horner 1982; Varricchio et al., 1997) and hole-nesting crocodilians and alligatorids (e.g., Kushlan and Simon, 1981; Mazzotti, 1989; Thorbjarnson, 1996).

The morphology of the Triassic nest ichnofossils and the pattern of their occurrence suggest that basic nest construction and architecture has remained relatively unchanged for over 200 million years. The ichnofossils imply that eggs were cared for through their deposition in excavated nests, rather then simply laid on the ground or in vegetation. This observation indicates that rudimentary parental care may have begun at least in the Triassic and may be even older, and is a major step toward the rearing of offspring and advanced parental care.
ACKNOWLEDGMENTS

We thank Timothy M. Demko and Howard Feldman for comments and suggestions to the manuscript. We also thank Jordi De Gilbert, Nicole Bonuso, Pat Quinn, and Todd Shipman for assistance in the field. The Petrified Forest Museum Association generously supported this research. This research is part of a Ph.D. dissertation by Stephen T. Hasiotis, at the University of Colorado, Boulder.


REFERENCES

Andrews, R.C., 1932. The conquest of Asia. American Museum of Natural History, New York.

Benton, M. J., 1997. Vertebrate Paleontology (second edition). Chapman and Hall, London, 452 p.

Bishop, G.A., N.B. Marsh, J. Barron, F.L. Pirkle, R.S.U. Smith, 1997. A Cretaceous sea turtle nest, Fox Hills Formation, Elbert Co., CO. Geological Society of America, Abstracts with Programs, 29(6):104.

Billingsley, G.H., 1985. General stratigraphy of the Petrified Forest National Park, Arizona. Bulletin of the Museum of Northern Arizona, 54:3-8.

Blakey, R. C., 1989. Triassic and Jurassic Geology of the southern Colorado Plateau. in, Jenny, J.P. and Reynolds, S. J., eds., Geologic Evolution of Arizona.

Arizona Geological Society Digest 17, p. 369-396.

______, and R. Gubitosa, 1983. Late Triassic paleogeography and depositional history of the Chinle Formation, southern Utah and northern Arizona: in, Reynolds, M. W. and Dolly, E. D., eds., Mesozoic Paleogeography of the West-Central United States. Rocky Mountain Section SEPM, p. 57-76.

______, and ______, 1984. Controls of sandstone body geometry and architecture in the Chinle Formation (Late Triassic), Colorado Plateau. Sedimentary Geology 17: 51-86.

Bock, B. C. and A.S. Rand, 1989. Factors influencing nesting synchrony and hatching success at a green iguana nesting aggregation in Panama. Copeia, 1989:978-986.

Bonaparte, J. F. and M. Vincent, 1979. El hallazgo del primer nido de dinosaurios triasicos (Saurischia: Prosauropoda), Triasico superior de Patagonia, Argentina. Ameghiana, 16:173-182.

Brannen, N.A. and G.A. Bishop, 1993. Nesting traces of the loggerhead sea turtle (Caretta caretta Linne), St. Catherine Island, Georgia: Implications for the

fossil record. in, Farrell, K. M., Hoffman, C. W., and Henry, V. J., Jr., eds., Geomorphology and facies relationships of Quaternary barrier island complexes

near St. Mary's, Georgia. Georgia Geological Society Guidebook, 13(1):30-96.

Carr, A., 1967. So excellent a fish: a natural history of turtles. The Natural History Press, American Museum of Natural History, New York, 248 p.

Carroll, R.L., 1964. The earliest reptiles. Journal of the Linnean Society, Zoology, 45:61-83.

Carroll, R.L., 1969. A middle Pennsylvanian captorhinomorph and the interrelationships of primitive reptiles. Journal of Paleontology, 43:151-170.

Cooley, M.E., 1958. The Mesa Redondo Member of the Chinle Formation, Apache and Navajo counties, Arizona. Plateau, 31:7-15.

______, 1959. Triassic stratigraphy in the state line region of west-central New Mexico and east-central Arizona. New Mexico Geological Society Guidebook of West-Central New Mexico, Tenth Field Conference, p. 66-73.

Cott, H.B., 1961. Scientific results of an inquiry into the ecology and economic status of the Nile crocodile (Crocodylus niloticus) in Uganda and northern Rhodesia. Transactions of the Zoological Society of London, 29:211-356.

Demko, T. M., 1995. Taphonomy of fossil plants in the Upper Triassic Chinle Formation: Ph.D. Dissertation, University of Arizona, 274 p.

______, R.F. Dubiel, and J.T. Parrish, 1998. Plant taphonomy in incised valleys: implications for interpreting paleoclimate from fossil plants. Geology, 26:1119-1122.

Dubiel, R.F., 1989. Depositional and climatic setting of the Upper Triassic Chinle Formation, Colorado Plateau. in, Lucas, S. G. and Hunt, A. P., eds., Dawn of the Age of Dinosaurs, New Mexico Museum of Natural History Spring Field Conference Guidebook, p. 171-187.

______, 1994. Triassic deposystems, paleogeography, and paleoclimate of the Western Interior: in, Caputo, M. V., Peterson, J. A., and Franczyk, K. J., eds., Mesozoic systems of the Rocky Mountain region, USA. Rocky Mountain Section, SEPM, Denver, Colorado, p. 133-168.

Dugan, B.A., A.S. Rand, G.M. Burghardt, and B.C. Bock, 1981. Interactions between crocodiles and iguanas. Journal of Herpetology, 15:409-414.

Grine, F.E. and J.W. Kitching, 1987. Scanning electron microscopy of early dinosaur eggshell structure: a comparison with other rigid sauropsid eggs. Scanning Microscopy, 1:615-630.

Hailman, J.P. and A.M. Elowson, 1992. Ethogram of the nesting female loggerhead turtle (Caretta caretta). Herpetologia, 48(1):1-30.

Hirsch, K.F., 1979. The oldest vertebrate egg? Journal of Paleontology, 53:1068-1084.

______, 1994. Upper Jurassic eggshells from the Western Interior of North America. in, Carpenter, K., Hirsch, K. F., and Horner, J. R., (eds.), Dinosaur eggs and babies, Cambridge University Press, Cambridge, p. 137-150.

______, K. Stadtman, W. Miller, and J. Madsen, 1989. Upper Jurassic dinosaur egg from Utah. Science, 243:1711-1713.

Horner, J.F., 1982. Evidence of colonial nesting and "site fidelity" among ornithiscian dinosaurs. Nature, 297:676-678.

______, and R. Makela, 1979. Nest of juveniles provides evidence of family structure among dinosaurs. Nature, 282:296-298.

Hunt, A.P., 1995. Stratigraphy and taphonomy of Late Triassic dinosaur localities, Petrified Forest National Park, northeastern Arizona. Program and Abstracts of Presented papers and Posters of the Third Biennial Conference of Research on the Colorado Plateau, p. 26.

______, T.P. Olson, P. Huber, T. Shipman, P. Bircheff, and J.E. Frost, 1996. A new theropod locality at Petrified Forest National Park with a review of Late Triassic dinosaur localities in the park. in, Boaz, D., Dierking, P., Dornan, M., McGeorge, R., and Tegowski, B. J., eds., Proceedings of the Fourth Annual Fossils of Arizona Symposium, Mesa Southwest Museum and Southwest Paleontological Society, Mesa, Arizona, p. 55-61.

Kirkland, J.I., 1994. Predation of dinosaur nests by terrestrial crocodilians. in, Carpenter, K., Hirsch, K. F., and Horner, J. R., (eds.), Dinosaur eggs and babies, Cambridge University Press, Cambridge, p. 124-133.

Kitching, J.W., 1979. Preliminary report on a clutch of six dinosaurian eggs from the Upper Triassic Elliot Formation, North Orange Free State. Paleontographica Africana, 22:41-45.

Kushlan, J.A. and J.C. Simon, 1981. Egg manipulation by the American alligator. Journal of Herpetology, 15:477-488.

Lapparent, A. and G. Zybyszewski, 1957. Les dinosauriens du Portugal. Memoires du Service Geologique de Portugal, 2:1-63.

Leslie, A.J., 1997. The ecology and physiology of the Nile crocodile, Crocodylus niloticus, in Lake St. Lucia. Kwazulu/Natal, South Africa (osmoregulation, estuary, sex determination). Unpublished dissertation, Drexel University, Philadelphia, Pennsylvania, 316 p.

Lockley, M.G., 1989. Middle Pennsylvanian paleoecology of the Eagle Basin region, central Colorado. 21st Congres International de Stratigraphie et de geologie du Carbonifere, Beijing, 1987, Compte redu 3:245-250.

Long, R.A. and P.A. Murray, 1989. Late Triassic (Carnian and Norian) tetrapods from the Southwestern United States. Museum of Northern Arizona Bulletin, 59:27-50.

Mazzotti, F.J., 1989. Factors affecting the nesting success of the American crocodile, Crocodylus acutus, in Florida Bay. Bulletin of Marine Science, 44:220-228.

Novell, M.A., J.M. Clark, L.M. Chiappe, and D.M. Dashzeveg, 1995. A nesting dinosaur. Nature, 378:774-776.

Padian, K., 1986. On the type material of Coelophysis (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 University Press, Cambridge, p. 45-60.

Repenning, C.A., M.E. Cooley, and J.P. Akers, 1969, Stratigraphy of the Chinle and Moenkopi Formations, Navajo and Hopi Indian Reservations, Arizona, New Mexico, and Utah. U.S. Geological Survey Professional Paper 521-B, p. B1-B31.

Smith, R.M.H., 1987. Helical burrow casts of therapsid origin from the Beufort Group (Permian) of South Africa. Palaeogeography, Palaeoclimatology, Palaeoecology, 57:285-331.

Stewart, J.H., F.G. Poole, and R.F. Wilson, 1972, Stratigraphy and origin of the Chinle Formation and related Triassic strata in the Colorado Plateau region with a section on sedimentary petrology by R. A. Cadigan and on conglomerate studies by W. Thordarson, H. F. Albee, and J. H. Stewart. U.S. Geological Survey Professional Paper 690, 336 p.

Thorbjarnson, J.B., 1996. Reproductive characteristics of the Order Crocodylia. Herpetologia, 52:8-24.

______, and G. Hernandez, 1983. Reproductive ecology of the Orinoco crocodile (Crocodylus intermedius) in Venezuela. I. nesting ecology and clutch relationships. Journal of Herpetology, 27:363-370.

Varricchio, D.J., F. Jackson, J.J. Borkowski, and J.R. Horner, 1997. Nest and egg clutches of the dinosaur Troodon formosus and the evolution of avian reproductive traits. Nature, 385:247-250.



Webb, G.J.W., W.R. Buckworth, and S.C. Manolis, 1983. Crocodylus johnstoni in the McKinley River area, N. T. VI. Nesting biology. Australian Wildlife Research, 10:607-637.

Woodward, A., T. Hines, C. Abercrombie, and C. Hope, 1984. Spacing patterns in alligator nests. Journal of Herpetology, 18:8-12.


База данных защищена авторским правом ©shkola.of.by 2016
звярнуцца да адміністрацыі

    Галоўная старонка