Paleontology is the study of pre-existing life based on fossils. A fossil can be an actual portion of the animal, such as bones, teeth, or shells, or may be replaced by minerals such as silica, iron, and manganese as in petrified wood. It can even be hair, hide, and dung preserved in permafrost of the Arctic or a dry cave in the desert. A fossil may also be a track or a trail, an imprint or a cast, anything that reveals information about preexisting life. Through paleontology, scientists hope to create a more complete understanding of how life has changed since it first appeared in the geologic record of time. When organic remains such as a plant or animal dies, it can be altered by sun, precipitation, other animals, and geological actions – and time and time again. This is called ‘taphonomy’. For our work here at The Mammoth Site, it is critical that we look at all aspects of our fossil discoveries.
The fossils from The Mammoth Site sinkhole include hundreds of bones and thousands of snail and clam shells. The huge mammoth bones (predominantly of the Columbian mammoth, Mammuthus columbi) are exciting to uncover and study. It is hard to imagine such a huge beast swimming around (and apparently drowning) in the sinkhole pond. But it often is the smaller species, the rodent tooth, fish skeleton, molluscan shell that helps us reconstruct past local environments.
The Mammoth Site – A Research Institution
The Mammoth Site locality is a sinkhole, one filled in with sediments and fossils. The sinkhole formed years ago when a cavern in the Minnelusa limestone collapsed. The collapse caused a vertical shaft called a breccia (BREH-chee-uh) pipe to form. The ground surface of Spearfish Shale, a red rock unit, also caved in, creating surface depression. This opened a sixty-five foot deep 120 by 150 foot sinkhole. This type of sinkhole is called “karst” (named after a region in Italy). The breccia pipe provided a chimney-like opening for a warm artesian spring to percolate up through the rocks to create a steeply-sided pond.
Presumably enticed by the warm water and pond vegetation, mammoths entered the pond to eat, drink, or bathe and then could not escape. The mammoths were unable to find a foothold to scale the steep, slippery shale banks. Trapped in the pit, the mammoths ultimately died of starvation, exhaustion, or drowning.
The watering hole slowly filled with layers of silt, sand, and some gravels, along with decaying mammoths. The ‘mud’, which had aided in trapping the mammoths, now entombed and preserved the mammoth skeletons.
Eventually the sinkhole filled, and the artesian spring diverted to the lower elevation of Fall River, as the river cut deeper in the valley floor. Over thousands of years, the “hardened mud plug” inside the dried-up pond has remained stable. The surrounding geological unit, the soft red Spearfish shale, easily eroded, leaving the sinkhole a hill.
The Mammoth Site is beginning a new project – the reconstruction of the Ice Age environments of the Black Hills. Although The Mammoth Site is and has been a critical dataset for this topic, the fossil site is a single locality and a single point in time…and it is biased toward capturing pretty much only mammoths. We need more fossil sites, more variety in types of animals, we need more geological localities, and we need to know their respective ages!
Whether we are looking at mammoths and other critters or plants or the Early Americans who might have been here utilizing the meat and plant resources available during the late Ice Age, these two resources are constantly reacting to weather and climate changes. Plants and animals react by changing their distributions based on temperature, precipitation, and the timing of both at the extremes. Over the past 2.2 million years the World, and surely the Black Hills too, has proceeded through at least 22 major shifts in climate, from a glacial maximum (Canada and more covered by 1 mile+ of ice) to an interglacial (such as we are in today). Can we find records of these shifts in climate? They would show up as different geographic distributions in the fossil record. Once we find these fossil sites, do we fully recognize them for what they are, and, most importantly, how old are these sites.
Chronology – how old is it?
What needs to be established first and foremost is an accurate age of The Mammoth Site. For years we have depended on a radiocarbon (14C) analysis using the bone apatite fraction from mammoth bones recovered from the site. This analysis states that the site is about 26,000 years old. This apatite compound is just not the best resource to use for an accurate radiocarbon date – but it was all that we had, all that we could find to use. All other organic fractions were just not turning up in the analyses – they were gone. At least two reasons can account for this. 1) The presumed warm water environment of the sinkhole pond has leached all organic remains out of the bone, so with no charcoal available either, all we had was bone apatite for an 14C analysis. 2) The site is older than what radiocarbon analyses can be used for. 14C is good back to about 50,000 years. Beyond this time, it becomes pretty sketchy as to whether or not we can get an accurate age. So maybe The Mammoth Site is NOT 26,000 years old but much older, greater than the 50,000 years that 14C allows us to assess.
Our answer is to analyze the age based on a different methodology; something other than 14C dating. Years ago Dr. Larry Agenbroad, then Chief Scientist at The Mammoth Site, tried a uranium series analysis. Back then the analysis still had its technical issues for producing accurate age estimates. A date of about 130,000 was determined but Dr. Agenbroad felt that this was just not in the realm of accuracy so the age was dismissed for logical reasons at the time. Thus, we kept with the 26,000 year age estimate. One problem is that the fauna just did not ‘look like’ an environment that would be dating 26,000 years old – a very cold time of our prehistoric past.
So now we are analyzing the age of the sinkhole contents using Optically Stimulated Luminescence (OSL). For this we extract out of the sediments (instead of bone); we have the US Geological Survey experts taking feldspar and quartz grains to analyze. Our site has loads of these minute crystals. We took multiple samples at the top of the site and many samples down at the bottom of the excavation (but remember that this is still 40+ft above what we think is the true bottom of the sinkhole). More about this soon.
Persistence and Other Caves
For the past few years The Mammoth Site and staff at Wind Cave National Park have a working partnership in the study of Persistence Cave. This tiny cave that seems to be more of a long tube filled with sediments and bones then a ‘classic cave.’ Hundreds of thousands of bones and teeth along with some plants and lots of snails are being recovered from the sediments that choke this winding cave. Radiocarbon ages go back to about 40,000 years so far. Some of the mammal species live today in the Black Hills, but others are nowhere to be found in the Hills. Some rodents live only to the east, others only to the north on into Canada. A relative of the cottontail rabbit (pika) is found no closer than the Bighorn Mountains to the west in Wyoming. Some of the lizards and snakes that we are recovering in the cave do not occur in the Black Hills today. Plus we are recovering bison, horse, and camel – all dating to the Ice Age.
Sandy Swift is washing pretty much all the removed cave sediments and then sorts all bone and teeth from the dried, wet-sieved remaining debris. Again, thousands and thousands of fossils are being recovered. Dr. Jim Mead, Mammoth Site Chief Scientist and Site Director is spearheading this project and works mainly with the reptiles, amphibians, and some of the smaller mammals and the bison. Dr. Chris Jass (Curator of Quaternary Paleontology, Royal Alberta Museum, Canada) is concentrating on the various species of vole rodents (his specialty).
There are a few other caves closer to Pringle that are showing signs of incredible Ice Age faunal remains. Two of these caves are being overseen by Dr. Chris Jass (via The Mammoth Site) while Dr. Jim Mead will spearhead the research on the reptiles and amphibians along with most of the large mammals should they be recovered, such as bison etc.
The Mammoth Site is taking a more prominent role to understanding the evolution and distribution through time of our National Mammal, the Bison. The Mammoth Site sinkhole does not have a record of bison…at least not yet. And there might be a good reason for this, but more on this in the near future!
Persistence Cave has a number of bison remains – of all ages. We are finding more and more bison localities around the Black Hills that have bison. Now we need to determine their ages. Jeff Martin is a Ph.D. student at the Texas A&M University where he is working on how (not if) climate directly affects the size (mass and overall stature) of bison today. His preliminary findings are interesting, startling, and relate to climate change of the past 10,000 years (including the recent changes!). Jeff is working with Dr. Jim Mead at The Mammoth Site – we are the ‘remote field station’ for his bison studies along with his work with Jim on bison from various sites around and within the Black Hills. Jeff and Jim worked together on the fossil bison from the Colorado Plateau of the Four Corner States region. They are currently working on the bison record from Southern Arizona and Northern Sonora, Mexico.
Olga Potapova, Mammoth Site Collections Manager, is also working on various aspects of bison, especially some remains from the frozen permafrost of Siberia. She is collaborating with colleagues including Albert Protopopov in Yakutia, Russia.
So you can see that besides the Ice Age iconic mammoth, The Mammoth Site is also including Bison as a focus of study.
You may not have realized that The Mammoth Site has a leading research lab with state-of-the-art comparative collections to study present, Holocene (past 11,000 years), and Ice Age (11,000+ years old) fossils. The Site has a tremendous comparative collection of DUNG! Why you ask? So an archaeological site in southern Texas has some dung in one layer. The archaeologist want to know what produced it, what did the animal eat, when, and why is that animal no longer in that region today. An ecologist discovered a dried dung mat in a shelter on Tiburon Island, a desert island in the Sea of Cortez, Mexico. The ecologist and his Mexican colleagues want to know all there is about this bighorn sheep on an island. A cave north of Tucson, Arizona, up in the Santa Catalina Mountains has a floor dung mat containing very large dung pellets – identical to the fossil dung pellets of the extinct Shrub-ox that Jim Mead studied from Bechan Cave (big poop cave in Navajo), Utah. Where does one go to study dietary remains preserved in dung remains – The Mammoth Site of course!
If someone needs to study fossil snakes, lizards, frogs, salamanders, mammals – The Mammoth Site is a place to go for North American remains. The collection has taken decades to develop. Thousands of bones of small mammals, lizards, and salamanders are being recovered from alluvium and shelters on islands of the Channel Islands National Park off the coast from Santa Barbara, California. Justin Wilkins and Dr. Jim Mead at The Mammoth Site are working on identifying these remains. Interestingly they just recovered and identified the first fossil frog (chorus frog) from the Ice Age of the Channel Islands. They are now focusing on the lizards and salamanders from a number of these deposits.