Analysis of Small Mammalian Taxa from Selected Levels of Main Cone 1, Parker s Pit. Cave System, South Dakota. Mark Shelleman

Transcription

1

2 Analysis of Small Mammalian Taxa from Selected Levels of Main Cone 1, Parker s Pit Cave System, South Dakota Mark Shelleman Abstract: In the summers of 2006 through 2008 sediment and animal material from the Parker s Pit Cave system, in South Dakota USA were collected (Graham, 2008) and brought back for further analysis. For the purpose of this study samples from selected levels of Parker s Pit Main Cone 1 were used. Based on the known habitats of the extant taxa today along with the sample s stratigraphic location in the cave a climatic picture can be painted. The samples indicate a colder climate deposited during the time of the last glacial event. A general cooling trend is seen as you move up stratigraphically. Using the knowledge of other known dated material from the Main Cone 1 site (Pardi, 2010) and looking at what the climate was during the last glacial these samples can be placed around the start of the Younger Dryas period. Carbon-14 dating will allow the date of these samples to more accurately established. ii

3 Table of Contents Acknowledgements.iv Introduction.1 Purpose of Study.4 Methods..5 Results 13 Discussion..17 Conclusion.19 References Cited 19 iii

4 Acknowledgments: I would like to thank Dr. Russell Graham for all his help, without him this study would not have been possible. The use of his lab and his knowledge as an advisor were invaluable. There are also many individuals who were involved in the collection of the samples that were used in this study that I must thank as well. The US Forest Service must also be thanked for permitting excavation of the site and study of the specimens. I appreciate the time that Dr. Peter Heaney has put into leading the senior thesis class. I also need to thank Dr. Peter Wilf for allowing me to use the photo-microscope in the paleobiology lab. Thanks also go out to Mike Donovan for taking time from his research to show me how to work said microscope. Special thanks go to my family for always pushing me and for all the support over the years. Words can t express what you have meant to me. iv

5 Introduction: About C ka (thousand years ago), (21 ka calendar years) was the Last Glacial Maximum (LGM) (Alley, 1999). This represents the furthest southern expanse of the Laurentide Ice Sheet (LIS). Other than the Younger Dryas (11 to 13 ka) (Alley, 1999), this marks the coldest the Earth has been in the last 125 kyr (thousand years). From around 14 ka till the present day the North American climate has been experiencing a general warming trend. This can be seen from ice core data and δ 18 O ratios as can be seen in Stuiver and Groots (1999). Along with the regression of the ice sheet the warming has led to the migration of biota. During the full glacial period the average annual temperature was 5 to 7 C cooler than it is today (Alley, 1999). During this time cooler flora and fauna will have extended further south than they are today. According to the FAUNMAP Working Group (1996) the migration of North American Holocene animal species tends to follow a Gleasonian model of migration. In this model individual species will migrate when they feel a stress from the environment, in this case the climate change (FAUNMAP, 1996). As opposed to an entire community migrating as a whole, as a response to stress factor. Caves are places where animal bone material can be preserved, especially small mammalian bones. Bones may have accumulated in the cave as a result of the animals crawling or falling into the cave and not been able to escape; living in the cave, or that they were brought there by predators. Raptors are huge contributors to animal material build up in caves (Graham, 1991). These caves can be important in interpreting the change in climate. The location of the cave does not change geographically, but the climate and subsequently the taxa that inhabit the cave at that point in time will change. 1

6 Small mammals, especially insectivores and rodents are very useful for climate studies, due to their inability to migrate large distances over short periods of time (Graham, 1986). Substantial number of these fossils can be found in deposits with adaptation to local environments (Graham, 1986). Another important factor is that most late Pleistocene and Holocene species are extant today (Graham, 1986). Study Area: Figure 1: Regional Location Map (Pardi, 2010) The Black Hills are located in southwestern South Dakota (Stebler, 1939), see Figure 1. It is an isolated forested Mountain range surrounded by plains. They are the result of an igneous uplift about 55 million years ago, as a result of the Laramide Orogeny (Hall et al, 2002). This range has been subject to erosion since the uplift (Hall et al, 2002). The Black Hills are a land island as they are the only uplift in the area and are isolated from the Rocky Mountains (Hall et al, 2002). As noted by Stebler (1939) there are large differences in the distribution of plants and animals between the Black Hills, the nearby Badlands and surrounding plains. This is in part due 2

7 to the difference in elevation, temperature, and moisture. The change in elevation of the Black Hills compared to the Badlands ranges between ft (Stebler, 1939). At the base of the Black Hills is a drier sagebrush environment (Hall et al, 2002). As one moves up in elevation hardwood forests are more abundant, however ponderosa pine forests make up the bulk of the flora covering the Black Hills (Hall et al, 2002). The fauna found in the Badlands is representative of the fauna of the Great Plains. Meanwhile the fauna of the Black Hills is a combination of Great Plains fauna and typical Rocky Mountain taxa (Stebler,1939). Of the taxa that were observed in this study, some of these species are present in the Black Hills today. There are a few overlapping species that occur in the Badlands and the Black Hills. Some examples are Tamias minimus and Neotoma cinerea (Stebler,1939). The Parker s Pit Cave System is located in the Black Hills of South Dakota (Graham, 2008). This particular pit cave system has multiple entrances and cave tubes, which have been excavated at various times. For this study selected levels of the Main Cone 1 (MC1) excavation site were used. Upon excavation of MC1 three stratigraphic units have been identified. As described in Graham (2008) the top two units are made up of poorly sorted sediments with clasts of broken limestone and intermixed bones. The top layer is dark blown to black transitioning to a more yellowish color in the layer below. The bottom of the three layers is a yellowish fossiliferous limestone (Graham, 2008). Parker s Pit (PP) is located south of what was the furthest extent of the ice sheet during the LGM (Dyke et al, 2002). Therefore, Parker s Pit was open to deposition throughout this interval of time and allows for MC1 to provide a nearly continuous record. As Hadly (1999) 3

8 points out, factors like inconsistent rates of sedimentation in caves, changes in community and predation, and general time averaging can lead to difference in abundance throughout time in caves. Purpose of Study: This study will look at bone material from selected layers of PPMC1 (Parker s Pit Main Cone 1) (Fig 2). This study will focus only on the small mammalian animals. Based on the current adaptations of taxa found in the samples, an environment can be established for that particular level and time. These environments and fauna will show the changing climate through time. My hypothesis is that the bone material should show that the climate was cooler than it is presently in the Black Hills. 4

9 Figure 2: Map of Parker s Pit (modified after Ohms, Walz & Shafer 4/2/05) showing major excavation areas (Main Cone1, Main Cone2, Red Cone, Red Cone, Back Cone and NW Extension Tube). Methods: Excavation and Field Methods: In the summers of 2006 through 2008, a team was sent to excavate various locations of the Parker s Pit Cave system (Graham, 2008). Sediment and bone material were extracted from Parker s Pit Main Cone 1 in 50 cm excavation squares, in 10 cm levels. Stratigraphic horizons were separated within each excavation level. Each sample was weighed after extraction to correct for differences in volume (Pardi, 2010). 5

10 Samples were screen-washed through 0.16 cm standard window screen over a wooden frame. Fine grained sediment was washed from the samples, to reduce the volume and weight of the samples. This helps the removal process of specimens by decreasing the sediment to fossil ratio (Pardi, 2010). After screen washing the samples are allowed time to dry and are then rebagged with their original labels. In a field lab, high grade picking was performed in order to retrieve delicate skull material (Pardi, 2010). The remaining material was brought back to The Pennsylvania State University Vertebrate Paleontology Laboratory for more thorough picking. Specimen Identification: Bones were removed from the high grade matrix of each sample bag via picking. After which specimens were identified using modern osteological collections and published descriptions (these are described as Keys to fossil taxa in Graham lab at Pennsylvania State University ). The majority of the specimens extracted are bone fragments or postcranial material (bone material behind the skull). This material tends to be hard to identify and are not typically useful for identification purposes. Teeth and jaw bone are often good indicators of genus and or species, and are used to make taxonomic identifications. Identifications were made in the Graham lab at Pennsylvania State University, under a microscope in order to see details at the dental level. Photographs of the specimens were taken in the paleobotany lab at Penn State, using a microscopic camera. Microtine Rodents: Microtine rodents have developed a set of molar teeth that are made up of loops and triangles. Each set of molars (the upper and lower) have an anterior and posterior loop (Fig 3). Triangles can either be open or closed depending upon their orientation with other triangles. The 6

11 most useful teeth are the upper third molar (M 3 ) and the lower first molar (M 1 ). The M 1 tooth is located in the front of the mouth and the M 3 subsequently in the rear of the mouth. Figure 3: Generalize dentition for a Microtine rodent. (Pardi, 2010) Voles: A significant amount of the specimens from all the samples, belong to the genus Microtus. However due to indistinguishable morphological dentition similarities the species often cannot be identified. Of the Microtus specimens found from the selected levels at PPMC1, they can be placed into two clades based on the lower M 1 morphology (Bell and Bever, 2006; Keys to fossil taxa; Pardi, 2010). 7

12 The 5-7 closed triangle clade would include species like Microtus pennsylvanicus and Microtus californicus. The 3 closed triangle clade include species like Microtus ochrogaster and Microtus pinetorum (Pardi, 2010). Both of these clades have cement within re-entry angles of triangles ideally, however it is missing sometimes in a specimen. 5-7 Closed Triangle Clade: The M 1 consists of a large posterior loop. Triangles 1-5 are closed. On the M 3 and M 2 there are hooks on the posterior loops. The size of the hook on the M 3 is large. Teeth are cemented and unrooted (Keys to fossil taxa). 3 Closed Triangle Clade: Figure 4: 5-7 closed triangle clade. Lower right dentition (M1, M2) Scale bar 1mm. The M 1 consists of a large posterior loop. Triangles 1-3 are closed. Teeth are cemented and unrooted (Keys to fossil taxa). 8

13 Figure 5: 3 closed triangle clade. Lower right dentition (M2, M3) Scale bar 1mm. Clethrionomys gapperi (Red backed vole): In the lower teeth, triangles open into each other. Typically 5 visible triangles on M 1 unless specimen is a juvenile. Can contain some cement. Teeth are rooted. Triangles are not as arched as in the closed triangle clades (Keys to fossil taxa). Phenacomys sp. (Heather vole): The M1 consists of a large posterior loop. The first 5 to 6 triangles are closed. Anterior loop on M1 is much smaller than other vole species. No cement and teeth are rooted (Keys to fossil taxa). 9

14 Figure 6: Phenacomys sp. Lower left dentition (M1, M2) Scale bar 1mm Cricetine Rodents: Peromyscus sp. (Deer mouse): Has low alternating cusps protruding on the M 1. This creates valleys in-between the cusps. Smaller than Onychomys. Shrews: Shrews are easiest to identify by their red teeth (found on almost all species in North America). The lower jaw of a shrew will have 3 molars in the back with a premolar. In front of that will be a varying amount of unicuspids with a long incisor in the front of the jaw. Of the shrews found in these samples that can be identified, there is Sorex arcticus and Sorex palustris (Keys to fossil taxa). The easiest way to tell the difference between the two species is the presence of a postmandibular foramen (pmf). Both of these species have a mandibular foramen (mf). This appears as a small hole towards the bottom rear of the lower jaw. Sorex palustris only has the mf and 10

15 therefore only has 1 hole. Sorex arcticus has both mf and pmf which results in two holes or the joining of the two holes to form a larger hole, as can be seen in Figures 7. Figure 7: Sorex arcticus. Lower left jaw. Scale bar 1mm. Mustelidae: Mustela sp. (Weasel): Figure 8: Sorex palustris. Lower right jaw. Scale bar 1 mm. Classification of individual species in the Mustela genus can be determined by dentistry measurements. The size indicated the species. This particular weasel specimen was a juvenile and contained mainly deciduous teeth. This specimen did have the presence of the lower M 1 11

16 molar which allows for measurements to be compared to other samples. Measurements were done under a microscope and are shown in Table 1. Upon comparison of other specimens of Mustela the specimen from my samples seems to be Mustela frenata or the long-tailed weasel. Though my specimen is on the low end of the range of other collections of Mustela frenata it is still larger than the other smaller weasels in the Mustela genus. Contributing factors to the smaller size could be things like sexual dimorphism and that this specimen was still a juvenile when it deceased. PPMC1 PPMC1 LBEC LBEC Colo. Colo. Units mm OR (mm) Mean (mm) OR (mm) Mean (mm) Length of M Width of M Table 1: Table of measurements of lower weasel jaws. PPMC1 specimen comes from sample Bag 1 from Level 10, Unit 2, elevation: of Parker s Pit Main Cone 1. For PPMC1 specimen 32 units = 3mm. LBEC (Little Box Elder Cave). Colo. (Cave system in Colorado). Both samples from LBEC and Colo. are measurements of Mustela frenata from the University of Colorado Studies Series in Earth Science No.6. Fauna of the Little Box Elder Cave Converse County Wyoming, pg Figure 9: Mustela sp. Lower Jaw (M1, DP4, DP3, DP2) Scale bar 1mm. 12

17 AnalyticalMethods: After completion of species identification a faunal list was created. This contains a count of each taxon per stratigraphic sample. From these lists an environmental analysis was created for each sample. Using the known preferred niche that a particular taxon inhabits today, the fossil species were assigned a habitat (or habitats) preference, as seen in Banfield, 1974, Higgins et al, 2002, and conversations with Graham. Particular habitats are only found in certain climate types. Using these assumptions, percentages of different habitats were calculated for each sample. This was done in Microsoft Excel. The diagrams then illustrate how the environments changed over time. Results: A faunal list was created using all specimens from each of the sample bags, to create counts (Table 2). This included non-skull or dental specimens. Each individual specimen receives a count of one regardless of size or completeness. All but Bag 8 gave workable amounts of data. For the purposes of most of the environment interpretations Bag 8 is not included as it would provide no useful information. 13

18 Excavation Locations Taxa Bag # 1 Bag # 12 Bag # 5 Bag # 3 Bag # 4 Bag # 8 Total Sorex arcticus Sorex palustris Sorex sp. (large) Sorex sp. (small) Soricidae Chiroptera Sylvilagus sp Sciuridae Tamias Tamiasciurs hudsonicus Thomomys sp Cricetidae Peromyscus sp Onychomys leucogaster Neotoma sp Clethrionomys gapperi Phenacomys sp Microtus : 3 triangle clade Microtus : 5-6 triangle clade Microtus sp Zapus sp Mustela sp Total Table 2: Faunal List of samples from PPMC1. Bags are ordered by excavation elevation. Since all of the bags are from the same stratigraphic unit, elevation serves as a relative time marker with the youngest sediment from the highest elevation and the oldest from the lowest. Bag 12 is from Unit 2, Level 9, elevation , weights 17 lbs. 4oz. (17 04 ), and excavated 8/15/2007. Bag 4: Units 2, Level 9, elev , wt , 8/15/2007. Bag 3: Unit 2, Level 9, elev , 8/15/2007. Bag 5: Unit 2, Level 9, elev , wt. 8 04, 8/15/2007. Bag 1: Unit 2, Level 10, elev , wt , 8/15/2007. Bag 8-67: Unit 2, Level 12, elev , wt , 6/27/2008. In order to determine the dominant environment and subsequent climate of each bag, niches were assigned to the taxon based on present day habitats. This can be seen in Table 3. The environment classified as prairie is comprised of dry grassland areas. This would be very similar to the conditions experienced in the Great Plains region of the central United States. Wet grasslands are regions of higher elevation or more precipitation. These regions don t have large expanses of woods and are predominantly open. Many of the taxa in the samples can be found in mixed forest localities. This classification includes deciduous and coniferous forests. This classification is in-between the two extremes. It is always the largest percentage of each of the 14

19 sample bags. The classification Tiaga is a boreal forest environment. This is predominantly conifer forests with low annual temperatures. A tundra environment is typical of arctic conditions. Vegetation is much sparser in these regions due to the temperatures. Environment Taxa Tundra Tiaga Mixed Forest Wet grassland Prairie Sorex arcticus x x Sorex palustris x Sorex sp. (large) Sorex sp. (small) x Soricidae Chiroptera x x x Sylvilagus sp. x x x x x Sciuridae Tamias x x Tamiasciurs hudsonicus x Thomomys sp. x x Cricetidae Peromyscus sp. x x Onychomys leucogaster x Neotoma sp. x Clethrionomys gapperi x Phenacomys sp. x Microtus : 3 triangle clade x Microtus : 5-6 triangle clade x x Microtus sp. x x x Zapus sp. x x Mustela sp. x x x x Table 3: List of taxa and what environment they can be found today. An x means that taxa can be found in that particular environment. PPMC1 Level 9 Unit 2 elev wt % 4% Bag #12 7% 15% Tundra Tiaga Mixed Forest Wet Grassland n = 27 48% Prairie Figure 10: Environmental Breakdown of Bag specimens were used. 15

20 PPMC1 Level 9 Unit 2 elev % 5% 5% Bag # 3 Tundra 29% Tiaga Mixed Forest n = 41 59% Wet Grassland Prairie Figure 11: Environmental Breakdown of Bag specimens were used. PPMC1 Level 9 Unit 2 elev wt % 1% Bag # 4 1% 12% Tundra Tiaga Mixed Forest Wet Grassland n = 75 52% Prairie Figure 12: Environmental Breakdown of Bag specimens were used. PPMC1 Level 9 Unit 2 elev wt % 2% 13% Bag # 5 Tundra Tiaga n = 63 33% 43% Mixed Forest Wet Grassland Prairie Figure 13: Environmental Breakdown of Bag specimens were used. 16

21 PPMC1 Level 10 Unit 2 elev wt % 7% 11% Bag # 1 Tundra 32% Tiaga Mixed Forest n = % Wet Grassland Prairie Figure 14: Environmental Breakdown of Bag specimens were used. Figures 10 through 14 are listed in descending order from towards the top of the cave entrance to the bottom, implying that the youngest sediments are towards the top of the cave. They will also have the highest listed elevation. Discussion: The coldest sample appears to be from sample Bag 12. The rest of the samples in increasing order of warmth are: Bag 4, Bag 3, Bag 1, and then the warmest being Bag 5. Though it is not showing a warming trend as was my initial hypothesis based on an assumption that the age was between ka, the samples do show a change in climate over time and represent a climate that was colder than it is in present times. This does not mean that this method is inadequate to identify changes in climate rather that the ages of the samples are from a different age (possibly ka) than was previously expected. As all of these samples are from the same stratigraphic unit, if they were to originate around a warmer interglacial time and move to a cooler glacial time the record would show a cooling trend. Based upon the environmental analysis the samples seem to support a colder climate, even in the warmest samples. This may have occurred during the last glaciations. The presence 17

22 of cold weather taxa such as Phenacomys sp. and Sorex arcticus help support this point. The lack of lemmings is worth noting and may be an indication as to when these samples are from. Species like Dicrostonyx richardsoni are only adapted to living in very cold climates. From conversations with Graham and as is apparent in Pardi s (2010) thesis, they go extinct sometime around 14 ka. This is probably caused from the warm period after the last full glacial around 14 ka. Some of the samples seem to indicate climates that would be suitable for Dicrostonyx. From the general cooling trend and the lack of Dicrostonyx the date for these samples likely is from around the start of the Younger Dryas. Figure 15: Delta 18 O curve for the last glacial period produced from the GRIP core. Younger Dryas is the darker green section in the Late Glacial section of the curve. More negative δ 18 O values indicate colder temperatures and more negative values indicate warmer temperatures. Best estimates of the age of the samples is from around the start of the Y.D. (Younger Dryas). In Figure 15 the Y.D. is the highlighted darker green area in the region of the δ 18 O curve that is labeled Late Glacial. As can be seen in Figure 15 the Y.D. is the major cold spike that occurred around 14 to 12 ka. It is not yet fully understood what causes the Y.D. There is one 18

23 date from PPMC1 stratigraphically above the ones in this study and it is from about 10 ka radiocarbon years (= 12 ka). Although other factors like stratigraphic mixing cannot be ruled out until radiocarbon dates can be used to confirm the age. Conclusion: Fossil material from Parker s Pit Cave Main Cone 1 documents a change in environments through time. Samples seem to show a general cooling trend as you move upwards stratigraphically Even the warmest samples indicate that these samples are from a cold period, by the presence of arctic and boreal forest taxa Best estimates for dates of these samples are from 13 ka around the last warmer period before entering the Y.D. References: Alley, R.B., P.U. Clark The Deglaciation of the Northern Hemisphere: A Global Perspective. Annual Review of Earth and Planetary Sciences, 27: Anderson, E The Carnivoria. Fauna of the Little Box Elder Cave Converse County, Wyoming. University of Colorado Studies Series In Earth Sciences No. 6. pp University of Colorado Press, Boulder. Banfield, A.W.F The Mammals of Canada. University of Toronto Press, Toronto. Bell, C.J., and Bever, G.S., Description and significance of the Microtus (Rodentia: Arvicolinae) from the type Irvington fauna, Alameda County, California. Journal of Vertebrate Paleontology, 26:

24 Dyke, A.S., J.T. Andrews, P.U. Clark, J.H. England, G.H. Miller, J. Shaw, J.J. Veillette The Laurentide and Innuition ice sheets during the Last Glacial Maximum. Quaternary Science Reviews, 21: FAUNMAP Working Group, Spatial Response of mammals to late Quaternary Environmental Fluctuations. Science, 272: Graham, R.W Response of Mammalian Communities to Environmental Changes During the Late Quaternary. pp In Community Ecology, J. Diamond and T.J. Case (eds.). Graham, R.W Owls, Caves and Fossils-Predation, Preservation, and Accumulation of Small Mammal Bones in Caves, with an Analysis of the Pleistocene Cave Faunas from Westburry-Sub-MenDip, Somerset, UK-Andrews, P. Science, 253: Graham, R.W Report of Excavation at Parker s Pit and Don s Gooseberry Pit in the Black Hills National Forest Black Hills of South Dakota August 2006 & August Graham, R.W., E.C. Grimm Effects of Global Climate Change on the Patterns of Terrestrial Biological Communities. Trends in Ecology & Evolution, 5: Hadly, E.A Fidelity of terrestrial vertebrate fossils to a modern ecosystem. Palaeoecology, Hall, J.S., H.J. Marriott, J.K. Perot Ecoregional Conservation In The Black Hills. The Nature Conservancy. Higgins, K.F., E.D. Stokel, J.M. Goulet and D.C. Backland Wild Mammals of South Dakota. South Dakota Department of Game, Fish and Parks, Pierre. Keys to fossil taxa in Graham lab at Pennsylvania State University Pardi, M.I Local and Broad Scale Changes In North America Small Mammal Community Structure: The Late Pleistocene Through The Late Holocene. Masters Thesis. Pennsylvania State University, University Park. 20

25 Stebler, A.M An Ecological Study of the Mammals of the Badlands and the Black Hills of South Dakota and Wyoming. Ecology, 20: Stuiver, M., P.M. Grootes GISP2 Oxygen Isotope Ratios. Quaternary Research. 53: