Ziegler Reservoir fossil site
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The Snowmastodon site, also known as the Ziegler Reservoir fossil site, is the location of an important Ice Age fossil excavation near
Snowmass Village, Colorado Snowmass Village is a home rule municipality in Pitkin County, Colorado, United States. The population was 2,826 at the 2010 census. A popular winter resort location for skiing and snowboarding, the town is well known as the location of the Sno ...
. Fossils were first discovered on October 14, 2010, during the construction of a reservoir to supply Snowmass Village with water. Over the subsequent weeks, after an agreement had been reached to allow paleontological excavation, crews from the
Denver Museum of Nature & Science The Denver Museum of Nature & Science is a municipal natural history and science museum in Denver, Colorado. It is a resource for informal science education in the Rocky Mountain region. A variety of exhibitions, programs, and activities help mus ...
and the U.S. Geological Survey worked along with the construction crews as more fossil material was uncovered. The site closed for five months over the winter, reopening May 15, 2011. Between May 15 and July 4, 2011, crews from the Denver Museum of Nature & Science conducted a large scale fossil excavation alongside construction crews building a dam for the reservoir. In total over 36,000 vertebrate fossils (including mammoths, mastodons,
ground sloths Ground sloths are a diverse group of extinct sloths in the mammalian superorder Xenarthra. The term is used to refer to all extinct sloths because of the large size of the earliest forms discovered, compared to existing tree sloths. The Carib ...
,
horses The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million yea ...
, camels and deer), more than 100 species of fossil invertebrates and over 100 species of fossil plants were found in sediments deposited by an alpine lake during the last interglacial period.


Discovery

The fossil site was discovered on October 14, 2010, by Gould Construction Inc. crews who had been employed by the Snowmass Water and Sanitation District (SWSD) to expand the
Ziegler Reservoir Ziegler is a common German-language surname meaning "brick-maker" and may refer to the following people: Actors * Ernst Ziegler (1894–1974), German actor *Lulu Ziegler (1903–1973), Danish actress * Matilda Ziegler (born 1964), English actress * ...
and provide additional water supplies to the nearby town of
Snowmass Village Snowmass Village is a home rule municipality in Pitkin County, Colorado, United States. The population was 2,826 at the 2010 census. A popular winter resort location for skiing and snowboarding, the town is well known as the location of the Sn ...
. While clearing the perimeter of the reservoir,
bulldozer A bulldozer or dozer (also called a crawler) is a large, motorized machine equipped with a metal blade to the front for pushing material: soil, sand, snow, rubble, or rock during construction work. It travels most commonly on continuous track ...
operator Jesse Steele unearthed the first animal bones. Recognizing them as possible fossils, Steele informed project foreman, Kent Olson. Olsen took the bones home and identified them as belonging to a mammoth using sources he found on the internet. The next morning, Kit Hamby, the district manager for the Snowmass Water and Sanitation District (SWSD), contacted a contractor from the Colorado Geological Survey who contacted the Denver Museum of Nature & Science (DMNS). The DMNS reached an agreement with the SWSD to allow the museum to excavate the fossils. Crews from the Denver Museum, U.S. Geological Survey, and several other institutions work alongside bulldozers for two weeks in order to salvage the increasing number of fossils being unearthed. The onset of winter caused the site to be closed for five months beginning November 15. When the excavation resumed on May 15, 2011, museum crews had 7 weeks to complete the excavation in order for the reservoir project to be completed on time. By the time excavation had been completed, the team consisting of more than 250 volunteers and 40 project scientists removed approximately 8000 cubic meters of sediment. Thousands of fossils were collected along with stratigraphic, geochronologic, palynologic, paleoentomologic, and paleobotanic data that was subsequently used to reconstruct the paleoecosystem at ancient Lake Ziegler.


Snowmastodon Project

A $10.5 million dam for the reservoir was scheduled to be completed by mid-October 2011, with the site was expected to be underwater by November 2011. For that reason, any paleontological excavation had to be done quickly. The excavations were led by the Denver Museum of Nature & Science, together with the U.S. Geological Survey and scientists from at least 19 institutions. The Snowmastodon Project, as the efforts had been dubbed, cost approximately $1 million, including public outreach programs. Half of the costs were covered by grants and gifts to the museum, while the rest came from donations. The first scientific excavation officially began on November 2, 2010. It involved 67 workers from the Denver Museum of Nature & Science, and lasted 12 days. Preliminary efforts concluded on November 14, 2010, when the arrival of winter prevented any further excavation. The site and fossils left ''in situ'' were protected with frost-free barrier and the recovered fossils taken to the conservation laboratory of the DMNS. More than 600 bones and 130 plant, rock, and invertebrate samples were recovered, including the first mastodon skull ever recovered in Colorado (unearthed a mere day after the beginning of the excavation) and the first remains of a Jefferson's ground sloth to be found in the state. Other
megafauna In terrestrial zoology, the megafauna (from Greek μέγας ''megas'' "large" and New Latin ''fauna'' "animal life") comprises the large or giant animals of an area, habitat, or geological period, extinct and/or extant. The most common threshold ...
recovered included
giant bison ''Bison latifrons'', also known as the giant bison or long-horned bison, is an extinct species of bison that lived in North America during the Pleistocene epoch ranging from Alaska to Mexico. It was the largest and heaviest bovid ever to live in ...
, two deer-like animals, and more mammoths. Excavations resumed during spring of 2011, from May 15 to July 4, with the support and permission of SWSD and the State of Colorado. By the end of July, the total number of bones recovered was around 36,000, from at least 52 different Ice Age vertebrate animals. Approximately 3,000 of them are believed to come from mastodons of both sexes and of varying ages, from infants to full adults. Other new animals recovered included an Ice Age camel, a horse, and various smaller vertebrates. A small excavation crew from the museum remained at the site, in the event further discoveries were made in the course of the dam construction. The speed at which the fossils were recovered (more or less seven weeks) is remarkable for a scientific dig of this size. Kirk R. Johnson, leader of the Snowmastodon Project on behalf of the Denver Museum of Nature & Science, told the New York Times, ''"The speed of this thing is so unlike normal science — from discovery to completion of one of the biggest digs ever in less than nine months."'' Scientists are not concerned now that the site is covered by water after completion of the reservoir expansion. Being underwater helps preserve the fossils and the reservoir can be drained if ever the need arises for additional excavations.


Importance

The Ziegler Reservoir fossil site is one of the few localities in North America from the Sangamonian Stage, and the only one at high elevation. This site preserves multiple alpine ecosystems stacked on top of each other within sediments of ancient alpine lake. Among the vertebrate fauna, this site represents highest known elevations of a number of species. Additionally, this site holds the record for the most mastodons preserved in a single location, including the largest mastodon ever found. The fossil flora offer unprecedented insights into plant biogeography of the Rocky Mountains during the last interglacial period. The site is also important for the exceptional preservation of fossil material. Fossil sedge and willow leaves were still green, conifer cones were still intact, and large driftwood logs were preserved. In addition, the mollusks and gastropods showed color, and beetle parts were still iridescent. Vertebrate fossil material was in excellent condition as well. The National Geographic Society, which donated a $55,000 grant to the project, featured the site in the '' National Geographic Magazine'' . The science television series ''
Nova A nova (plural novae or novas) is a transient astronomical event that causes the sudden appearance of a bright, apparently "new" star (hence the name "nova", which is Latin for "new") that slowly fades over weeks or months. Causes of the dramati ...
'' broadcast an episode about the site in February, 2012.


Geologic setting and geochronology

The Ziegler Reservoir occupies an unusual geologic setting on top of a ridge above sea level. The lake basin was formed when a glacier flowing down Snowmass Creek Valley became thick enough to overtop the adjacent ridgeline. As the glacier retreated, a moraine impounded a 5 hectare alpine lake that was initially 10 meters deep. Over time, the lake filled in with wind-blown sediments until it became a marshland and ultimately an alpine meadow. After Doug Ziegler and his family purchased the land that now contains the Ziegler Reservoir, they commissioned the construction of a small earthen dam in 1961 to block the meadow drainage and form a shallow, private lake that persisted until the Snowmass Water and Sanitation District bought the water rights in 2010. Several dating techniques were employed in order to determine the age of the ancient lake sediments. Attempts at radiocarbon dating of lake organics, bone collagen and shell carbonate, revealed that the site was radiocarbon dead or greater than 45,000 years old. ''In situ'' cosmogenic beryllium and aluminum from a boulder that was part of the bounding moraine yielded an age of approximately 140,000 years old. Uranium-series dating of vertebrate fossils confirmed the age range of 45,000-140,000 years; however, the extremely low uranium concentrations limited the utility of that method. Optically stimulated luminescence (OSL) ages obtained from the fine-grained quartz provided reliable, replicable ages for the sediments within the established 45,000 – 140,000 time frame. The dates obtained via OSL correlate with the end of the Bull Lake glaciation and the Sangamon interglacial stage, spanning marine isotope stages 6 through 4.


Vertebrate fauna

Over 36,000 bones and teeth belonging to 52 taxa of macro- and microvertebrates were uncovered during the construction of Ziegler Reservoir. These taxa represent a diverse assemblage of fauna belonging to the Rancholabrean North American Land Mammal Age. The smaller vertebrate species include: trout, frog, salamander, snake,
lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...
, duck, goose, pheasant, crane, finch, shrew, river otter,
bear Bears are carnivoran mammals of the family Ursidae. They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats throughout the Nor ...
,
coyote The coyote (''Canis latrans'') is a species of canis, canine native to North America. It is smaller than its close relative, the wolf, and slightly smaller than the closely related eastern wolf and red wolf. It fills much of the same ecologica ...
,
rabbit Rabbits, also known as bunnies or bunny rabbits, are small mammals in the family Leporidae (which also contains the hares) of the order Lagomorpha (which also contains the pikas). ''Oryctolagus cuniculus'' includes the European rabbit speci ...
, chipmunk,
squirrel Squirrels are members of the family Sciuridae, a family that includes small or medium-size rodents. The squirrel family includes tree squirrels, ground squirrels (including chipmunks and prairie dogs, among others), and flying squirrels. Squ ...
,
beaver Beavers are large, semiaquatic rodents in the genus ''Castor'' native to the temperate Northern Hemisphere. There are two extant species: the North American beaver (''Castor canadensis'') and the Eurasian beaver (''C. fiber''). Beavers ar ...
,
mice A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...
and other small
rodents Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are nat ...
. The most abundant species found throughout the site is the tiger salamander. Also represented in the Ziegler Reservoir are the remains of seven megafauna taxa. These taxa include: * Columbian mammoth (''Mammuthus columbi''): Four individuals, including the first fossil recovered from the site (a juvenile nicknamed 'Snowy') were collected. * American mastodon (''Mammut americanum''): The Ziegler Reserver is the largest site for mastodons in the world with at least 35 individuals present. Approximately 60% of the total number of vertebrate elements recovered belong to the American mastodon. * Jefferson's ground sloth (''Megalonyx jeffersonii''): Three individuals, one adult and two juveniles, were found at the site. This marks the first time this species has been found in Colorado. *
Giant bison ''Bison latifrons'', also known as the giant bison or long-horned bison, is an extinct species of bison that lived in North America during the Pleistocene epoch ranging from Alaska to Mexico. It was the largest and heaviest bovid ever to live in ...
(''Bison latifrons''): At least 10 individuals were found making the Ziegler Reservoir one of only three sites to produce multiple individuals of ''B. latifrons'' and the highest known elevation for this species. * Deer: At least two individuals of indeterminate species. * Camelops: A single tooth belonging to the extinct camel genus ''Camelops'' was found in lake-center deposits. This is the highest known elevation for this genus. * Horse: A single foot bone from an indeterminate species of ''
Equus Equus may refer to: * ''Equus'' (genus), a genus of animals including horses, donkeys and zebras * ''Equus'' (play), a play by Peter Shaffer * ''Equus'' (film), a film adaptation of the Peter Shaffer play * Equus (comics), a comic book characte ...
''.


Invertebrate fauna

; Fossil insects A total of 99 taxa of insect were identified from samples spanning the interval of 125,000 to 77,000 years ago. These fossils are the oldest known Pleistocene high elevation insect faunas from the Rocky Mountains. The fossil assemblages were dominated by
beetles Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...
, ants,
midges A midge is any small fly, including species in several families of non-mosquito Nematoceran Diptera. Midges are found (seasonally or otherwise) on practically every land area outside permanently arid deserts and the frigid zones. Some midg ...
, and caddisflies, which were used to document the climatic oscillations during the time represented by the samples. ; Mollusks and ostracodes Sediments containing terrestrial and aquatic
mollusks Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000  extant species of molluscs are recognized. The number of fossil species is esti ...
and
ostracods Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typical ...
span 130,000 to 87,000 years ago. These sediments produced 12 identifiable taxa of terrestrial gastropods, 5 taxa of aquatic bivalves, 8 taxa of aquatic gastropods, along with 7 taxa of ostracodes. These taxa indicate that the ancient lakeshore was a shallow, well-vegetated, fresh water wetland during the time periods sampled.


Fossil flora

A diverse assemblage of plant macrofossils and
pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...
was collected during Snowmastodon. Approximately 99 taxa of plant macrofossil, including
seeds A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosperm pl ...
,
leaves A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...
, needles, cones,
twigs A twig is a thin, often short, branch of a tree or bush. The buds on the twig are an important diagnostic characteristic, as are the abscission scars where the leaves have fallen away. The color, texture, and patterning of the twig bark are ...
and wood were identified. Over 300 specimens of fossil wood were collected ranging in size from small stems to logs greater than 50 cm in diameter and more than 10 m in length. The majority of wood fossils came from the “beach” horizon at the lake margin. Species of
fir Firs (''Abies'') are a genus of 48–56 species of evergreen coniferous trees in the family (biology), family Pinaceae. They are found on mountains throughout much of North America, North and Central America, Europe, Asia, and North Africa. The ...
,
Douglas fir The Douglas fir (''Pseudotsuga menziesii'') is an evergreen conifer species in the pine family, Pinaceae. It is native to western North America and is also known as Douglas-fir, Douglas spruce, Oregon pine, and Columbian pine. There are three va ...
,
spruce A spruce is a tree of the genus ''Picea'' (), a genus of about 35 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal (taiga) regions of the Earth. ''Picea'' is the sole genus in the subfami ...
and pine were represented. The pollen collected includes species of sagebrush, spruce, pine, oak, Douglas fir, fir,
juniper Junipers are coniferous trees and shrubs in the genus ''Juniperus'' () of the cypress family Cupressaceae. Depending on the taxonomy, between 50 and 67 species of junipers are widely distributed throughout the Northern Hemisphere, from the Arcti ...
, as well as
herbaceous Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials. Definitions of "herb" and "herbaceous" The fourth edition of t ...
and
aquatic plants Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or macrophytes to distinguish them from algae and other microphytes. A macrophyte is a plant that ...
.


See also

* Denver Museum of Nature and Science * List of fossil sites * Pitkin County, Colorado * Pleistocene megafauna *
Snowmass Village, Colorado Snowmass Village is a home rule municipality in Pitkin County, Colorado, United States. The population was 2,826 at the 2010 census. A popular winter resort location for skiing and snowboarding, the town is well known as the location of the Sno ...
*
Southern Rocky Mountains The Southern Rocky Mountains are a major subregion of the Rocky Mountains of North America located in the southeastern portion of the U.S. state of Wyoming, the central and western portions of Colorado, the northern portion of New Mexico, and ex ...


References

{{Reflist, 30em


External links


"Ice Age Death Trap"
Episode of PBS's ''
Nova A nova (plural novae or novas) is a transient astronomical event that causes the sudden appearance of a bright, apparently "new" star (hence the name "nova", which is Latin for "new") that slowly fades over weeks or months. Causes of the dramati ...
'' on the Snowmastodon excavation project, broadcast February 1, 2012 (archive; introduction only) 2010 in paleontology Cenozoic paleontological sites of North America Geography of Pitkin County, Colorado Paleontology in Colorado