A Systematic Review of the Fossil Lizards and Snakes (Squamata) from the White River Group of Badlands National Park

Dennis Maddox1 and William P. Wall2

1
Department of Physiology, Medical College of Georgia, Augusta, GA 30901
2Department of Biology, Georgia College & State University, Milledgeville, GA 31061


Abstract—A general survey of the Squamata from the White River Group (37.0 to 26.9 MYA) from Badlands National Park is presented. New specimens are examined and described. Life habits of the fossil taxa are inferred from comparison with close living relatives where possible. Arboreal taxa are absent from the White River fauna. Since the Badlands region was open forest during much of that time, the absence of these taxa is probably the result of taphonomic bias. The reduction in herpetofauna diversity in this region during the Oligocene is believed to be the result of increasing aridity rather than the decline in temperature.

Introduction

Paleontologists have collected vertebrate fossils from the sedimentary deposits of the Big Badlands in South Dakota since the late 1800's. Cenozoic squamates, however, because of their scarcity and fragmentary nature, have not enjoyed a great deal of attention over the years. Leidy (1851), Cope (1877), and Marsh (1890) were the first paleontologists to extensively study fossil reptiles from the Big Badlands. After more than one hundred years of study much confusion exists regarding these fossil squamates. Part of this problem is due to the misidentification of juvenile specimens as separate taxa from adults of the same species. Other taxa were named without giving sufficient consideration to intraspecific variation.

This paper, first, attempts to clarify some of the systematic confusion regarding the fossil lizards and snakes from the White River Group preserved in Badlands National Park. Second, based on interpretation of the life habits of these organisms, we hope to relate the herpetofauna to the habitats available in the Badlands region during the Oligocene.


Stratigraphy And Paleoecology

The rocks of Late Eocene through Oligocene age (37 - 27 million years ago) bear the majority of vertebrate fossil material (Clark, 1937; Clark, Beerbower, and Kietzke, 1967; Harris and Tuttle, 1977). The lowest unit of the White River group is the Chadron Formation. Deposition of this layer began during the Late Eocene time period, approximately 37million years ago as determined by 40Ar/39Ar dating (see Prothero, 1994 for stratigraphic columns). It is divided into the Ahearn Member, the Crazy Johnson Member, and the Peanut Peak Member. Overlying the Peanut Peak Member of the Chadron is the Brule formation, and it is subdivided into the Scenic Member, and the Poleslide Member. Overlying the Poleslide Member of the Brule is the Sharps Formation. Prothero (1994) recently established that the Arikaree Member of the Sharps Formation was deposited during the late Oligocene. The Chadronian, Orellan, Whitneyan, and Arikareean land mammal "ages" were named from the White River Group.

The Eocene/Oligocene transition was a time of great change throughout the world, in both climate and species diversity (Clark, Beerbower, and Kietzke, 1967; Savage and Russell, 1983). The general trend was a transformation from an early Eocene rain forest type environment to a climate that was more like the modern arid semideserts (Prothero, 1994). Evidence from plant and marine fossils, and oxygen and carbon isotopes indicates that a significant cooling trend began about 50 million years ago and continued through the Oligocene. Hutchison (1992) compiled a listing of all the late Eocene through early Oligocene herpetofaunal taxa of North America. He determined that the percentage of aquatic taxa was decreasing during this time.

Materials And Methods

The Georgia College & State University vertebrate paleontology (GCVP) collection houses the majority of specimens studied. Additional specimens from the South Dakota School of Mines and Technology (SDSM) and The Pratt Museum at Amherst College (ACM) were examined. Recent squamates from the Georgia College & State University herpetology collection (GCH) were used for comparative purposes. All material is identified, described, and placed in the correct stratigraphic position. Interpretations of life habits and climatology are based on analysis of fossil organisms, the depositional sedimentology of the area in which the fossil was found (when possible), and by comparing the fossil organism to modern relatives (when applicable). Relative abundance for each taxon over time is based on specimens in the GCVP collection.

All measurements were taken with Helios dial calipers to 0.05mm. Pictures of Rhineura floridana and Rhineura hatcherii were taken using a Polaroid model 618091 Microcam, an Olympus 20X binocular dissecting microscope, and a Dazor model 364 flexlight. These images were then scanned into a computer and modified using Adobe Photoshop and Illustrator software.

Systematic Paleontology

Order Squamata Merriam, 1820

Family Anguidae Gray, 1825

Genus Peltosaurus Cope, 1873

Peltosaurus granulosus Cope, 1873

Peltosaurus abbotti Gilmore, 1928

Peltosaurus piger Gilmore, 1928

Peltosaurus floridanus Vanzolini, 1952

Holotype.—American Museum of Natural History (AMNH 1610).

Referred Material.—ACM 3900, left jaw fragment; GCVP 2130, partial skull and associated scutes; GCVP 2281, partial skull; GCVP 2429, partial skull; GCVP 2589, jaw fragment; GCVP 3015, partial skeleton and associated dermal osteo-scutes; GCVP 3124, skull fragment and vertebrae; GCVP 3466, partial jaw with one tooth; GCVP 3483, fragmentary skull and jaw; GCVP 4266, jaw fragment; GCVP 4267, cranial scute; GCVP 4268, parietal scute; GCVP 4383, 2 dermal osteoscutes; SDSM 3189, complete skull with articulated dermal scutes and partial skeleton.

Diagnosis.—Gilmore (1928) lists the following as characteristics of Peltosaurus: Seven teeth on premaxillary; 10 teeth on the dentary; parietal bone broad and flat; frontals greatly narrowed and united; postorbital and postfrontal coalesced; parietal in contact with squamosal; head and body covered with unkeeled, finely granular scutes.

Remarks.—Peltosaurus abbotti is generally accepted as a valid taxon because its skull is greatly convex and its appearance is, as a result, drastically different from that of Peltosaurus granulosus. Recently, however, Sullivan (personal communication) has stated his opinion that the type specimen of Peltosaurus abbotti was probably an aberrant individual and, therefore, he considers the species invalid.

Age Distribution.—Known; Chadronian through Arikareean. Most abundant; Orellan.

Modern Relatives.—Modern members of the family Anguidae include the genera Ophisaurus (legless glass lizards) and Gerrhonotus ("alligator" lizard). Since Ophisaurus is a legless, burrowing lizard, it is Gerrhonotus that gives the better idea of the possible habits of peltosaurs. Gerrhonotus is a relatively slow-moving lizard with a prehensile tail. Its diet includes insects, spiders, newborn mice, small snakes, and lizards. It is restricted mainly to Texas.

Genus Helodermoides Douglass, 1903

Helodermoides tuberculatus Douglass, 1903

Glyptosaurus tuberculatus Gilmore, 1928

Glyptosaurus montanus Gilmore, 1928

Glyptosaurus giganteus Gilmore, 1928

Holotype.—Carnegie Museum Catalogue No. 707

Referred Material.—GCVP 1256, dermal osteoscutes; GCVP 2121, dermal armor; GCVP 2132, 4 vertebrae; GCVP 2138, dermal armor; GCVP 3365, heavy cephalic armor; GCVP 3991, dermal armor; GCVP 3992, dermal armor; GCVP 3999, dermal armor.

Diagnosis.—Sullivan (1979) offers these characteristics as diagnostic of Helodermoides: frontals distinct; cephalic osteoderms bulbous; tubercles numerous, usually without definite arrangement (rarely a ring pattern is found on body osteoderms); six or seven rows of cephalic osteoderms between orbits; teeth subconical, posterior ones slightly recurved; jugal blade curved; maxilla straight; dentary moderately slender; supratemporal fenestra closed; skull highly vaulted. Remarks.—The GCVP collection has a small sample of Glyptosaurine material. The only specimens that are available are dermal osteoscutes (GCVP 6128, 6129, 6130, and 6131) and a small portion of the cranial region of one individual (GCVP 6132). This material is tentatively identified as Helodermoides tuberculatus because the cephalic osteoderms do not demonstrate concentrically arranged patterns of tubercles.

Age Distribution.—Known; Chadronian through Orellan. Most abundant; Chadronian through Orellan.

Modern Relatives.—Same as for Peltosaurus.

Family Rhineuridae Vanzolini, 1951

Genus Rhineura Cope, 1861

Rhineura hatcheri Baur, 1893

Gilmoreia attenuatus Taylor, 1951

Lepidosternon sp. Gilmore, 1928

Pseudorhineura minuta Vanzolini, 1951

Rhineura amblyceps Taylor, 1951

Rhineura attenuatus Estes, 1983

Rhineura coloradoensis Gilmore, 1928

Rhineura hatcherii Baur, 1893

Rhineura hibbardi Taylor, 1951

Rhineura minutus Gilmore, 1938

Rhineura sternbergii Walker, 1932

Rhineura wilsoni Taylor, 1951

Holotype.—Princeton University, Yale Peabody Museum (YPM-PU 11389).

Referred Material.—GCVP 2223, skull and jaws; GCVP 2224, partial skull; GCVP 2707, partial skull; GCVP 3628, skull and jaws; GCVP 3686, skull and jaws; GCVP 3935, partial skull and jaws; GCVP 4068, skull and jaws.

Diagnosis.—A compact well-ossified skull, with pleurodont teeth lacking the postorbital and postfrontal squamosal arches and epipterygoid (Gilmore, 1928).

Remarks.—Sullivan and Holman (1996) question whether Rhineura is the proper generic name for the fossil amphisbaenids from the White River Group. We believe that the fossil specimens show a definite affinity with the Rhineurinae. We do, however, recognize two differences between R. hatcherii and R. floridana. First, the teeth of R. floridana are less robust and more recurved than are those of R. hatcherii (Figure 1). Second, the parietal regions of the skulls of R. hatcheri and R. floridana appear to vary greatly with R. hatcherii having a visibly more expanded parietal re
gion. Parietal expansion was measured across the widest point of the squamosals, skull lengths were measured from the midpoint of the occipital condyle to the anterior tip of the premaxillary. All of our skulls of R. hatcherii are more brachycephalic than R. floridana. The smallest difference in ratios is between GCH 100 and GCVP 4068, 4.9%. If the expansion of the parietal area in R. hatcherii holds true for a larger sample size and a variety of age groups, this characteristic may be a useful diagnostic trait at the specific (or possibly the generic) level.

Age Distribution.—Known; Orellan through Whitneyan. Most abundant; Orellan.

Modern Relatives.—Rhineura floridana is the only extant member of the genus found in North America. Its body is segmented like that of an earthworm, but is covered in scales. This animal is adapted for burrowing and has no external eyes, limbs, or ear openings. Its range is restricted to the Florida peninsula where it lives in sand or soil and eats earthworms, spiders, and termites.

Family Boidae Gray, 1825

Subfamily Erycinae Bonaparte, 1831

Genus Calamagras Cope, 1873

Calamagras angulatus Cope, 1873

Ogmophis angulatus Cope, 1874

Holotype.—American Museum of Natural History (AMNH 1654).

Referred Material.—GCVP 1864, five articulated vertebrae, Poleslide Member of the Brule; 3410, two articulated vertebrae, Scenic Member of the Brule.

Diagnosis.—The vertebrae of Calamagras are characterized as having short, thick neural spines. The vertebral centra of Calamagras are less than 9mm. The neural spine is less than one-half the total length of the centrum, but it is not tubular or dorsally swollen (Holman, 1979).

Remarks.—Holman (1979) believed this poorly defined small boa-like snake might have had vestiges of hind limbs. Calamagras is a member of the Infraorder Henophidia, and general characteristics for this group include: neural arches usually vaulted, condyles and cotyles usually round, foramina usually lacking on either side of the cotyles, and hemal keel poorly developed.

Age Distribution.—Known; Orellan through Arikareean. Most abundant; Orellan.

Modern relatives.—Calamagras is similar to the living North American genera Lichanura and Charina (Holman,1979). L. trivirgata, the Rosy Boa, inhabits rocky brushlands and deserts (Stebbins,1966). A burrowing snake, it is attracted to oases and permanent or intermittent streams and feeds on small mammals and birds. Charina bottae, the Rubber Boa, is a good swimmer, burrower, and climber, frequenting grasslands, woodlands, and forests. It is usually found under rocks, logs, or the bark of fallen trees, generally feeding on small mammals and lizards.

Figure 1—Oblique side views of skulls of A, Rhineura hatcheri and B, Rhineura floridana showing differences in dental curvature.

Genus Geringophis Holman 1976

Geringophis vetus Holman, 1982

Holotype.—University of Kansas (KU 49126)

Referred Material.—GCVP 3460, 2 associated vertebrae.

Diagnosis.—This erycine boid is distinct from the other small boid genera found in the White River Group in that it has a flattened shape and a long, high neural spine. Holman (1979) describes Geringophis as having a "… unique combination of vertebral characters of a depressed neural arch, a long, well-developed, dorsally swollen neural spine, and a distinct hemal keel and sub-central ridges."

Remarks.—Geringophis vetus is the earliest occurrence of the genus Geringophis in the fossil record. It is quite interesting because of the variation of its vertebrae from the normal boid pattern. Sullivan and Holman (1996) state, "Whether this genus arose from Cadurcoboa [from the late Eocene of France] and immigrated to North America from the Old World, or originated from an erycine boid with a flattened vertebral form such as Calamagras angulatus, is unknown". Two other members of this genus are known: Holman (1979) reports G. depressus from the Lower Miocene of Nebraska and G. yatkolae from the Upper Miocene of Nebraska.

Age Distribution.—Known; Orellan. Most abundant; Orellan.

Modern relatives.— See Calamagras.


Discussion

Retallack (1992) stated that during the Orellan the Badlands region was open forest. It is necessary therefore, to explain the absence of any arboreal herpetofauna from the White River Group. The only herpetofauna observed from this time period are fossorial or ground dwelling, and if the area were, in fact, open forest, it seems that arboreal herpetofauna should be represented in the fossil record. This discrepancy, however, may be the result of taphonomic bias. The ground-dwelling forms had heavy dermal armor and their life habits may have increased the likelihood of preservation.

Prothero (1994) emphasized the decrease in temperature during the Eocene/Oligocene as the major climatic factor affecting species diversity. Hutchison (1992), however, stated that the increase in aridity (and accompanying decrease in aquatic habitats) had a greater impact on species diversity than the change in temperature. The squamate fauna tends to support Hutchison's interpretation. Aquatic lower vertebrates could find some measure of protection from cold weather by hibernating under water. The terrestrial vertebrates, however, would be more susceptible to cold weather. The aquatic lower vertebrates, particularly the boas, show a significant decline in abundance by the end of the Orellan. Since terrestrial lower vertebrates continue to flourish into the Whitneyan and Arikareean, it seems likely that the lack of aquatic habitats probably had the greater impact on squamate species diversity.


Acknowledgements

We thank Dr. Philip Bjork (SDSM) and Dr. Margery
Coombs (ACM) for access to specimens in their respective collections. We also thank Ms. Rachel Benton of Badlands National Park for her extensive support of our research efforts. We both benefited greatly from discussions with Dr. Dennis Parmley on the anatomy and systematics of fossil and recent squamates. Thanks are also due Dr. Robert Sullivan for providing us with useful insights on squamate identification and systematics. We thank Ms. Linda Chandler for the drawings presented in Figure 1. We thank three anonymous reviewers for their useful comments. Finally we thank Mr. Vince Santucci for his enthusiasm and support for paleontological research in the National Parks. This research was partially funded by faculty research grants from Georgia College & State University.

References

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