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The Wannagan Creek Quarry and Its Reptilian Fauna

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The Wannagan Creek Quarry and Its Reptilian Fauna >. l1J >C\J :51'­ THE WANNAGAN CREEK QUARRY AND ITS <fl.o Ciz Uc .- 0 REPTILIAN FAUNA 0'1. _ 0 ...... -0 000 J QJ.­ IBULLION CREEK FORMATION, PALEOCENE ~ ...... Vl o QJ ...... > o c IN BILLINGS COUNTY, NORTH DAKOTA ~­ 0""­ 0 0 .J::. ..... .... ­0 by '-0. Ow Za::: Bruce R. Erickson REPORT OF INVESTIGATION NO. 72 NORTH DAKOTA GEOLOGICAL SURVEY Don L. Halvorson, Stale Geolo~st 1982 ')(' WAN NAGAN CREEK QUARRY NORTH DAKOTA Loc~\ion and aerial view (inse\) of Wannagan Creek Quarry site looking east. THE WANNAGAN CREEK QUARRY AND ITS REPTILIAN FAUN A (BULLION CREEK FORMATION, PALEOCENE) IN BILLINGS COUNTY, NORTH DAKOTA by Bruce R. Erickson I.. I REPORT OF INVESTIGATION NO. 72 r • NORTH DAKOTA GEOLOGICAL SURVEY Don L. Halvorson, State Geologist 1982 Prinled by Associated Printers, Inc., Grand Forks, ND 58201 1982 CONTENTS Page INTRODUCTION . 1 Historical Review 1 Acknowledgments 1 Geologic Setting . 2 QUARRY SIGNIFICANCE 3 Wannagan Creek Assemblage 3 Reptiles of Wannagan Creek 4 Taphonomy . 6 Paleoecology . 10 Evidence of Predation 11 Evidence of Nesting 14 SUMMARY .. 15 REFERENCES 16 ILLUSTRATrONS Frontispiece Location and aerial view (inset) of Wannagan Creek Quarry site looking east Figure Page 1. Lower jaw halves of a multituberculate, SMM P74. 24 .130 (top), and a primate, Pleisiadapis SMM P78 .14.61 (below) indicate the nature of the small mammal community of Wannagan Creek Quarry . 2 2. Articulated skeleton of Leidyosuchus formidabilis, SMM P74.24.6 length approx. 3.5 meters 4 3. Field sketch of alligator skeleton, SMM P72. 34.274 (posterior two-thirds) in situ showing extznsive scutellation of the caudal region . 6 4. Skull of fish-eating Champsosaurus, SMM P77. 33.24, showing the delicate cranial structures . 7 5. Section of map of Wannagan Creek Quarry illustrating the development of beach cusps and locations of associated vertebrate remains . 9 6. Diagrarrunatic reconstruction of Wannagan Creek Quarry site during the Paleocene . 10 7. The carapace (upper shell) of Protochelydra, SMM P75. 22.271 shows wounds inflicted by large crocodile teeth .. ..... 12 8. Shell differences in two snapping turtles, Protochelydra, SMM P75. 22.271 (Paleocene) and Chelydra (recent common snapper), SMM uncatalogued specimen ..... 13 9. A fragmented crocodile metatarsal, SMM P74.22.329 from the beach facies of Wannagan Creek Quarry shows the telltale marks of gnawing, presumably by small scavenging mammals . .. 14 INTRODUCTION of aU the broken and weathered sur­ face materials for possible future Historical Review reference. Included in the hundreds of pieces recovered by this method were During the late summer of 1970 the many other crocodile bones and several author visited Paleocene exposures in more condyles as well as numerous western North Dakota to search for turtle and fish fragments, some small reported crocodile remains. Evidence of marrunal jaws, and a tiny bird bone. fossil crocodilians in the Dakota bad­ This survey clearly established the lands is not, in itself, cause for presence of a sizable group of animals surprise or even perhaps much in­ and perhaps a potentially important terest, as their osteoscutes (bony paleoecological site. plates) and vertebrae are among some Wannagan Creek Quarry was of the oldest known and most common opened the following year in 1971, and fossils of the West. The rather spec­ it has been intensively worked each tacular sample collection upon which subsequent year. During this period. the report was based, however, excavation has removed considerable deserved more than casual consider­ overburden resulting in a quarry ation; for among some 40 odd pieces of which presently encompasses some weathered bone, which had been 1,500 square meters (13,500 square collected the year before, were six feet). This effort has yielded a re­ occipital condyles of large adult croco­ markable fauna and flora in situ. It diles. The occipital condyle is a heavy, includes all classes of vertebrates, a solitary, bony structure at the back of modest number of invertebrates, and the skull that articulates with the first some interesting trace fossils in the vertebra of the backbone. Six of these form of burrows (Melchior and meant that at least six individual Erickson, 1979). crocodiles were represented--a rather Large amounts of matrix are high number for the limited sample. brought back from the quarry each This initial collection was made by year and subjected to a wet sieving Evelyn Sheldrup in 1969 while vaca­ treatment that separates the diminutive tioning in the area. It is not unusual bones and teeth from the matrix and in the annals of paleontology that retains them in fine mesh baskets. The significant discoveries have been made smaller jaw (fig. 1) is an example of by nonpaleontologists who were not in such a microfossil that probably would search of fossils. Too frequently, have gone undiscovered if it had not however, such discoveries go unre­ been collected in a sieve. corded. In the present case, Mrs. Because the great majority (over Sheldrup is to be commended for 70 percent) of the vertebrate animals bringing these materials to our atten­ found here are previously unknown to tion. science, the entire suite of specimens After a brief search, the exposure is collectively referred to as a "New from which the fossils were originally Fauna" and will henceforth be called collected was located and an examina­ the Wannagan Creek Fauna. tion of the site was begun. The large Each year additional new species number of bone fragments lying on the have been recovered. Until 1977 the surface of the ground at first sug­ rate of discovery of previously un­ gested a mere "bone hed"--a place identified species rose each year. where many bones had been deposited During that year alone nine new taxa and disassociated from one another by were documented. Considering the the action of water currents. Upon scope of the biota and the investi­ closer investigation it was revealed gating yet to be done, it is intended that, even though most of the visible that this discussion serve primarily as fragments were scattered at random, an introduction to the Wannagan Creek complete bones lying just beneath the Quarry community. surface were still intact and articulated with each other much as they had been Acknowledgments in life. This indicated that perhaps a complete skeleton might be found if a The writer is grateful to W. careful excavation were undertaken. Langston and J. Lang for helpful In order to begin a scientific suggestions on fossil crocodilians and excavation, a grid system was em­ discussions of behavior in living croco­ ployed to make a systematic collection dilians. Appreciation is extended to A. Figure 1. Lower jaw halves of a multituberculate, SMM P74.24.130 (top), and a primate, Plesiadallis SMM P78.14.61 (below) indicate the nature of the small mammal community of Wannagan Creek Quarry. Cvancara and C. Carlson for important Badlands exposures here comprise contributions to the text and to R_ Late Paleocene clastics (weakly con­ Melchior for reading the manuscript. solidated sedimentary rocks) of the K. Sander provided figure 4 and Bullion Creek (=Tongue River; Clayton frontispiece and R. Spading provided et a1. , 1977) and Sentinel Butte all of the photographs. Much of the Formations of the Fort Union Group. research related to this report was These rock units were derived from supported by the Geneste M. Anderson sediments carried eastward by streams Paleontology Fund. flowing from the rising Rocky Moun­ tains, and consist of fluvial and Geologic Setting lacustrine sands, silts, clays, lignites, and limestones. The contact between Wannagan Creek Quarry (frontis­ the two formations is clearly marked piece) is located in the "upper breaks" by a prominent lignite bed (the HT of the Little Missouri River in Billings lignite; Royse, 1972) which is trace­ County, North Dakota. Runoff water in able for considerable distances. the area is delivered to the river by Wannagan Creek Quarry occupies a numerous tributaries that have deeply stratigraphic position some 20 meters eroded the bedrock and produced a (66 feet) below this major lignite bed badlands topography. One of the within the Bullion Creek Formation. largest streams is Wannagan Creek The quarry is on the summit of a from which the site takes its name. ridge that: is isolated on all sides but Steep vertical rock faces, slump blocks, the south. It is in a remnant of a local and earthflows further characterize the flood basin in which sediments accumu­ area. lated during a period of quiescence 2 and, therefore, form an uninterrupted QUARRY SIGNIFICANCE sequence. A lower gray silt containing many Wannagan Creek Assemblage pelecypods (clams) and a few gastro­ pods (snails) represents the initial Wannagan Creek Quarry has phase in the development of a back­ yielded a diverse biota with a verte­ swamp environment. This is overlain brate biota that would rival that of by a dark lignitic shale primarily made any extant crocodile-dominated habitat up of locally produced organic material. except for an absence of large mam­ It contains abundant crocodile and mals. Smaller vertebrates are repre­ turtle bones in addition to many deli­ sented by more than 30 species com­ cately preserved tree leaves. This bed prising a variety of fishes, amphibians, grades upward into a fine gray silt birds, and mammals. Their abundant that again contains many vertebrates, remains are found in the silt and clay but fewer plant fossils. Crocodiles are sediment and are recovered through still present at this horizon and sev­ laboratory processing of that material. eral varieties of fishes and plants There are several chelonians appear for the first time in the quarry (turtles) in this fauna. These are sequence. These new species and the represented by numerous individuals of fine-grained sediments suggest that a various age groups.
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