ROBERT M. CHANDLER AND WILLIAM P. WALL
Dept. of Biology, Georgia College & State University, Milledgeville, GA 31061
AbstractThree bird eggs from the Scenic Member of the Brule Formation, Badlands National Park, Shannon County, South Dakota are the first published record of eggs from the early Oligocene (Orellan) of North America. The fossil eggs compare closest to gruiform birds: cranes, rails, limpkins, and their relatives (Aves: Gruiformes) in size, shape, and eggshell porosity. Our understanding of the Paleogene paleo-avifauna is based on fossil skeletons from a limited number of well-known Eocene and fewer Oligocene localities. Eocene and Oligocene gruiform bird species are known; one of which is the earliest record of a limpkin, Badistornis aramus Wetmore, from Shannon County, South Dakota. The eggs described herein compare closest to eggs of the living Limpkin, Aramus guarauna.
Beginning in 1987 field crews from Georgia College & State University (GC&SU) have intensively surface-collected fossiliferous beds in the Brule Formation in the South Unit of Badlands National Park. While mammal fossils comprise the majority of specimens contained in the Badlands strata, there is a significant herpetofauna as well (Maddox & Wall, 1998; Wall & Maddox, 1998).
Few bird fossils have been found in the Badlands National Park and the surrounding area over the 150 years of paleontological studies there. In general, our understanding of Paleogene birds is from species known from the Eocene of France, North America, and the United Kingdom (Feduccia, 1996:167-171). Therefore, any additional information about Paleogene birds, and especially pertaining to the Paleocene and the Oligocene, is important. This paper provides the first record of bird eggs from the early Oligocene (Orellan) of North America.
[An asterisk (*) indicates genera and species described from the Badlands National Park. The following acronyms are used: Georgia College & State University, Vertebrate Paleontology collections (GCVP); Museum of South Dakota School of Mines & Technology (SDSM)].
(cranes, rails, limpkins, and their relatives)
cf. *Genus Badistornis
cf. *Badistornis aramus Wetmore 1940
Holotype.- SDSM 3631, left tarsometatarsus missing the hypotarsus, collected in the Metamynodon zone river channel sandstone of the Brule beds, Upper White River (Orellan), Shannon Co., South Dakota.
Badistornis aramus Wetmore (1940:30) is the earliest record for a limpkin in North America (Brodkorb, 1967:155). In his "Remarks" section, Wetmore states, "The close general resemblance of the fossil specimen to the metatarsus of the living Aramus scolopaceus [=A. guarauna] is such as to leave no doubt almost at glance that it is a species of the family Aramidae." The tarsometatarsus of Badistornis aramus is slightly longer than that of the Limpkin: holotype = 155mm vs. A. guarauna = 113-123mm (n=6, Gilbert, et al., 1981:234). However, osteologically the characteristics of the holotype are that of a limpkin.
New material: Three bird eggs from the Southern Unit of Badlands National Park (Fig. 1 A-C). Two of the specimens (GCVP 3610 and 3682) were found near the southern end of Cedar Butte (GC&SU locality SDS 12). The third egg (GCVP 3958) is from the southern end of Big Corral Draw (GC&SU locality SDS 9; Fig. 3).
Description: GCVP 3610 (Fig. 1A) is in the best state of preservation of the three eggs, with little or no distortion and only slight cracking. Its overall geometry (elongation average, bicone average, asymmetry; as defined by AOU, 1962:13; Preston, 1953:166; Preston, 1968) is elliptical in profile and equal to that of the Aramidae (Preston, 1969:248, Table 1). The porous nature of the eggshell is preserved and compares well with that of Limpkin eggs (Fig. 2).
GCVP 3682 is slightly more distorted by compression than GCVP 3610 with many more cracks (Fig. 1B). Although not as well preserved, the elliptical geometry and the porous nature of the eggshell is still apparent.
GCVP 3958 is in the poorest state of preservation with numerous cracks and
flattening. However, the elliptical geometry and porous nature of the eggshell
is preserved (Fig.1C).
All three eggs were x-rayed but no embryos or internal structures were observed.
Measurements: GCVP 3610 = length 58.11mm x width 44.13mm; GCVP 3682 = [54.56]mm x [46.12]mm; GCVP 3958 = [55.46]mm x [39.08]mm; Limpkin (Aramus guarauna) 55-64mm x 41-47mm (Walters, 1994:82).
|Figure 1. A, GCVP 3610; B, GCVP 3682; C, GCVP 3958; and D, egg from a modern Limpkin (Aramus guarauna) as illustrated in Walters (1994). Scale bar equals 2 cm.|
|Figure 2. Detailed view of GCVP 3610 showing the porosity pattern characteristic of the eggshells of limpkins.|
Fossiliferous exposures in the gullies where these eggs were collected are Orellan (Scenic member, Brule Formation) in age. All the eggs were collected in float, but based on the stratigraphy of the fossil-bearing horizons a more narrowly defined time interval can be inferred.
GCVP 3610 was collected approximately 15 meters above ground level. Based on the mammal fauna (particularly Miniochoerus gracilis) contained in the only fossil-bearing horizon above that level in the gully, the most likely age for this egg is approximately 32.5 million years (early in Chron C12r of Prothero and Whittlesey, 1998). The same gully produced an unusually high frequency of Leptictis dakotensis specimens (three skulls and four lower jaws in less than two man hours of collecting). While this taxon has no biostratigraphic value its abundance in this gully may have some paleoecologic significance.
GCVP 3682 was collected in a gully approximately 200 meters from the gully containing GCVP 3610. This egg was collected at ground level just below a narrow fossil-rich horizon (approximately 2 meters thick) in a nodular zone. This locality also produced specimens of Ischyromys parvidens therefore the most likely age for this egg is 33 million years (Chron C13n of Prothero and Whittlesey, 1998).
GCVP 3958 was collected in float approximately 10 meters above the Metamynodon channel sandstone. The Orellan section in this locality is highly fossiliferous over multiple horizons, therefore this specimen cannot be assigned with confidence to a specific Chron but it is clearly younger than the early Orellan.
Retallack (1983, 1992) recognized four major habitats in Badlands during the Orellan. These are: streamside swales, near stream, open forest, and savanna. Based on the lithology and associated fauna at the bird egg localities these areas were most likely near stream or open forest habitats. Prothero provides a useful overview of paleoclimate anf faunal composition during the early Oligocene in North America.
In overall geometry (elongation average, bicone average, asymmetry) and eggshell porosity, and texture GCVP 3610 compares closest to the egg of the Limpkin, Aramus guarauna. GCVP 3682 and 3958 both compare very closely to GCVP 3610. An extinct limpkin, Badistornis aramus Wetmore, has been described from essentially the same locality (using identical stratigraphic, lithologic, and age criteria). Although B. aramus did have slightly longer tarsometatarsi than A. guarauna, overall the birds would be of very similar body size and weight. It can be surmised that these two closely related species of North American limpkins would have had eggs of similar size and shape. There are other extinct birds represented in the fossil record during the early Oligocene such as a guan and a quail (Galliformes: Cracidae, Phasianidae, respectively), a hawk (Falconiformes: Accipitridae), and an extinct relative of the modern seriema (Bathornithidae), but all of these living birds have eggs of a very different shape and/or size.
There is a published record of an early Miocene possible duck egg from South Dakota (Farrington, 1899). However, the collecting data is simply "region of the Bad Lands" and, therefore, the age is also questionable. O'Harra (1920:143) cites Farrington's report and states that there are other badlands bird eggs in museums, as was also noted by one of our reviewers, but as yet these are unstudied and unpublished specimens and are, therefore, not science.
We agree with the modern bird literature, e.g., Pettingill (1985:296), that modern bird eggs are best identified in the nest with an adult either sitting on the nest or identifying the species before it flushes from the nest, however, the birds that laid the eggs described herein flushed many millions of years ago.
Figure 3. Map of Badlands National Park showing general locality information. The enlarged portion of the map is modified from Harris et al., (1995).
We thank Dr. Rachel Benton of Badlands National Park for her extensive support of our research efforts and Mr. Vince Santucci for his enthusiasm and support for paleontological research in the National Parks. We would like to thank Ms. Linda D. Chandler and two anonymous reviewers for critically reading the manuscript. Linda Chandler also helped with illustrations. Ms. Elaine Zeiger, Geology Department, Field Museum of Natural History, provided a copy of the Farrington publication. Dr. Sara Toni Hall took x-rays of the bird eggs and discussed the results with RMC. This research was partially funded by faculty research grants from Georgia College & State University.
American Ornithologists' Union, 1962. Handbook of North American Birds. R.S. Palmer (ed.). Yale University Press, New Haven and London, Vol. 1, 567 pp.
Brodkorb, P., 1967. Catalogue of fossil birds: Part 3 (Ralliformes, Ichthyornithiformes, Charadriiformes). Bulletin of the Florida State Museum, Biological Sciences, 11(3):99-220.
Farrington, O.C., 1899. A fossil egg from South Dakota. Field Columbian Museum, Geological Series, Publication 35, v. 1(5):193-200.
Feduccia, A., 1996. The Origin and Evolution of Birds. Yale University Press, New Haven and London, 420 pp.
Gilbert, B. M., L.D. Martin, and H.G. Savage, 1981. Avian Osteology. B. Miles Gilbert, Publisher, 252 pp.
Harris, A. G., E. Tuttle, and S.D. Tuttle, 1995. Geology of National Parks. Kendall/Hunt Publishing Company, Dubuque, 758 pp.
Maddox, D. and W.P. Wall, 1998. A systematic review of the fossil lizards and snakes (Squamata) from the White River Group of Badlands National Park. National Park Service Paleontological Research Vol. 3 Technical Report NPS/NRGRD/GRDTR-98/1, pp.4-7
O'Harra, C.C. 1920. The White River Badlands. Bulletin No. 13, Department of Geology, South Dakota School of Mines and Technology, Rapid City, South Dakota. 181pp.
Pettingill, O.S.,Jr., 1985. Ornithology in laboratory and field. 5th ed. Academic Press, Harcourt Brace Jovanovich, San Diego, 403pp.
Preston, F.W., 1953. The shapes of birds' eggs. The Auk 70(2): 160-182
_____ , 1968. The shapes of birds' eggs: mathematical aspects. The Auk 85(4):454-463.
_____, 1969. Shapes of birds' eggs: extant North American families. The Auk 86(2):246-264.
Prothero, D.R., 1994. The Eocene-Oligocene transition. Paradise Lost. Columbia University Press, New York, 283 pp
_____ and K.E. Whittlesey, 1998. Magnetic stratigraphy and biostratigraphy of the Orellan and Whitneyan land mammal "ages" in the White River Group. Pp.39-61 in: D.O. Terry, H.E. LaGarry, and R.M. Hunt (eds.), Depositional Environments, Lithostratigraphy, and Biostratigraphy of the White River and Arikaree Groups (late Eocene to early Miocene, North America). Geo. Soc. Amer. Sp. Paper 325.
Retallack, G.J., 1983. A paleopedological approach to the interpretation of terrestrial sedimentary rocks: the mid-Tertiary fossil soils of Badlands National Park, South Dakota. Geological Society of America Bulletin 94:823-840.
______, 1992. Paleosols and changes in climate and vegetation across the Eocene/Oligocene boundary. in Eocene/Oligocene Climate and Biotic Evolution. Princeton University Press: New York. pp.382-398
Wall, W.P. and D. Maddox, 1998. Reassessment of characteristics determining generic affinity in Gopherus and Stylemys (Testudinidae) from the White River Group, Badlands National Park. National Park Service Paleontological Research Vol. 3 Technical Report NPS/NRGRD/GRDTR-98/1, pp.8-12
Walters, M., 1994. Birds' Eggs. Dorling Kindersley, London, New York, Stuttgart, 256 pp.
Wetmore, A., 1940. Fosssil bird remains from Tertiary deposits in the United States. Journal of Morphology, 66(1): 25-37.