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Mammalia – Mammals Xenarthra – Sloth Megalonyx jeffersonii – Jefferson's ground sloth PowerPoint Presentation
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Mammalia – Mammals Xenarthra – Sloth Megalonyx jeffersonii – Jefferson's ground sloth

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STUCKY, Richard(1), SERTICH, Joseph(1), JOHNSON, Kirk R.(1), MILLER, Ian(1), FISHER, Daniel C.(2), GRAHAM, Russell W.(3), MCDONALD, H. Gregory(4), and PIGATI, Jeffrey S.(5)

(1) Denver Museum of Nature & Science, 2001 Colorado Blvd, Denver, CO 80205,, (2) Museum of Paleontology and Department of Geological Sciences, University of Michigan, 1109 Geddes Ave, Ann Arbor, MI 48109-1079, (3) Earth and Minerals Science Museum, Pennsylvania State University, University Park, PA 16802, (4) Park Museum Management Program, National Park Service, 1201 Oak Ridge Drive, Suite 150, Fort Collins, CO 80525, (5) U. S. Geological Survey, Denver Federal Center, Box 25046, MS-980, Denver, CO 80225

The Snowmastodon Site, Pitkin Co., Colorado was discovered in October 2010 by heavy equipment operators during construction to expand a reservoir. The site was originally a lake formed at 8,874 feet during the Bull Lake glaciations about 150,000 years ago. The original lake area is approximately 11.5 acres in size with a total catchment of 25 acres and lacks an inlet and outlet. The sediments at the site are approximately 10 meters thick and include local gravity and debris flow deposits, airborne fine grained silts and clays, peat beds, and locally derived glacial deposits. Fossiliferous Pleistocene sediments range in age from approximately 130,000 years ago to ~45,000 years ago. Forty vertebrate taxa are currently identified from skeletal material and include the following preliminary identifications. Fish: Oncorhynchus. Amphibians: Ambystoma, several Rana species, and a potential hylid. Squamate reptiles: natricine and crotalid snakes, and two lizards. Birds: a duck (Anas),goose (Anser), grouse (Dendropagus), and a finch (fringilid). Mammals: sloth (Megalonyx jeffersonii), shrew and bat (Sorex andlarge microchiropteran), mink or weasel (Mustela), otter (Lontra), chipmunk (?Tamias), ground squirrel ( Spermophilus), a heteromyid rodent, a geomyid rodent, two genera of voles (two species of Microtus and Myodes), field mice (Peromyscus and Reithrodontomys), a jumping mouse (zapodid), muskrat (Ondatra), beaver (Castor), rabbit (Lepus), Columbian mammoth (Mammuthus columbi), mastodon (Mammut americanum), bison (Bison latifrons), sheep (Ovis), camel (Camelops), deer (Odocoileus), and horse (Equus), and several other taxa. Twp large carnivores are represented only by bone gnaw marks. Two stratigraphically distinct faunas are represented: Mammuthus is only represented in the uppermost peat deposit while Mammut and Megalonyx only occur in lower debris flow and lake margin deposits. Vertebrate specimens from the upper peat level are commonly articulated or associated, in contrast with lower deposits where most specimens are disarticulated due to modest pre- and syndepositional transport. Excavations are complete at the site but more than 3000 kg of matrix remain to be screen-washed and sampled for medium to small vertebrates.

There are two principle faunalzones: The upper peat/clay layers produce mammoth, bison, camel and deer. The lower silt and debris flow layers produce mastodon, sloth, bison, deer, camel and a majority of the other vertebrates. Vertebrates from the upper layers are generally articulated while those from the lower levels primarily consist of isolated bones.

View to east of the Snowmastodon site at Zeigler Reservoir.

Humerus of Lontra canadensis (Left) and Lontra sp. from Snowmass (Right)

Zapodidae M2

Fringilidae premaxilla

Sorex sp. M1-2

Annotated list of fossil vertebrates from the

Snowmastodon Site, Pitkin County, Colorado

Osteichthyes – Fish

Oncorhynchus clarkii – Cutthroat Trout

Trout are represented by small vertebrae of fingerlings. Less than a dozen specimens have been discovered.

Amphibia – Frogs and Salamanders

Ambystoma tigrinum – Tiger Salamander

The tiger salamander is the most abundant vertebrate in the fauna with thousands of specimens estimated to be preserved in the sediments (several thousands collected) including a complete skull and associated lower jaws. Terrestrial, neotenic, and cannibalistic morphs appear to be represented.

Anura spp. – Frogs

Four species are included, the Genus Rana (at least two species), and two additional species including a very small potential hylid or tree frog. One frog cranium or brain case has been found.

Squamata– Lizards and Snakes

Natricinae sp. – Garter snakes

Relatively rare with fewer than 20 specimens known at present, all vertebrae.

?Crotalidae sp. – Rattlesnakes

Several vertebrae have a strong ventral process suggesting affinities with rattlesnakes.

Lacertilia spp. – Lizards

Fragmentary vertebrae and one limb bone (distal humerus) are known. Size differences in the vertebrae suggest two species may be represented.

Aves – birds

Anas sp.– Ducks

Ducks are represented by a coracoid and humeri

Anser sp. – Geese

A single proximal humerus represents a goose .

Dendrogapus sp. – Grouse

A sacrum represents remains of a grouse.

Fringilidae sp. – Finch

A nearly complete premaxilla represents a finch of medium size.

Aves sp. – Birds

Additional taxa of birds are represented by vertebrae and limb elements that have not been studied.

Mammalia – Mammals

Xenarthra – Sloth

Megalonyx jeffersonii – Jefferson's ground sloth

At least three individuals are represented by skull material and front limb bones including one juvenile. First record from Colorado and specimens are from highest elevation for this species.

Soricomorpha -- Shrew

Sorex sp. – Shrew

A maxilla preserving an M1-2 represents a soricid shrew.

Chiroptera -- Bat

Chiroptera sp. – Bat

A single radius of a chiropteran is larger than any extant Colorado bat.

Carnivora – Dogs, weasels, bears

Mustela sp.-- mink/weasel

A small mink or weasel is represented by a small canine .

Lontra sp. – Snowmass otter

Otters are extremely rare in the fossil record. The Snowmass otter is represented by a humerus that has the distinctive anatomy of an otter.

Canidae/Ursidae sp. – dogs and bears

Gnaw marks from two sizes of carnivores (large size, bear or large canid, and medium size, medium to large canid) represent evidence for at least two scavengers/predators but the bones of either animal have not been recovered.

Rodentia -- Rodents, Beavers and Mice

Castor sp. – Beaver

The Beaver is represented by a fragmentary ulna and by gnaw marks on wood.

Microtus spp (two species) – Voles

At least two vole species are represented among the five specimens known at the site. These include isolated teeth and two jaws.

Myodes sp.– Red backed vole

Several molars represent the red backed vole.

Muridae sp. – Mice

A fragment of the p4 represents a larger Microtine rodent that is about the size of a woodrat. The specimen represents an additional taxon but is too fragmentary for identification to generic level.

Rodentia -- Rodents, Beavers and Mice.

Ondatra sp. – Muskrat

Muskrat is represented by an isolated molar and a femur. Although the tooth specimen is of a size similar to that of Ondatra zibethicus, the femur is about 25% longer than any specimen of this species in the modern DMNH collections.

Peromyscus sp. – Deer Mice

Deer mice are represented by isolated teeth.

Reithrodontomys sp. – Harvest Mice

Several specimens represent a harvest mouse.

Tamias sp. – Chipmunk

A single upper jaw (maxilla) of a chipmunk is represented.

Spermophilus lateralis – Golden-mantled ground squirrel

A frontal bone and teeth are comparable in size and morphology to that of the golden-mantled ground squirrel.

Heteromyidae sp. – Kangaroo rat

A kangaroo rat is represented by a single isolated molar.

?Geomyidae sp.– Pocket gopher

 A single tooth fragment represents a geomyid rodent.

Zapodidae sp. – Jumping mouse

An M2 of a jumping mouse displays a morphology similar to living jumping mice but is more primitive representing a distinct genus.

Lagomorpha – Rabbits, hares and pikas

Lepussp. – rabbits and hares

One vertebra and two fragmentary femora of a rabbit are known at the site from the lower debris flow/silt and shoreline deposits.

Proboscidea – Elephants, Mammoths and Mastodons

Mammut americanum – American Mastodon

Mastodons are by far the most common large mammals. The 2011 season collection includes a high frequency of young and older individuals, including several individuals with pathologies including broken bones, such as ribs and vertebrae, and fused elements. Also some animals show evidence for broken bones that healed during the lifetime of an animal (ribs and vertebrae). Mastodons are known from diamicton and silt deposits of the lower horizons and deposits along the shore line along the depositional basin margin.

Mammuthus columbi– Mammoth

Columbian mammoths are found only from clay and peat layers in the upper fossil deposits. At least two partially associated skeletons are known from the site including the original mammoth discovery at Snowmass. An unusual association of large boulders and a partial skeleton of a mammoth were excavated in a single field jacket that weighed 5 tons which was brought back for preparation in the laboratory. This specimen, known as the “clay mammoth,” preserves articulated vertebrae, the skull and lower jaws, and part of the imbs of the skeleton. Detailed preparation is being done to determine the complete taphonomic history of this unique specimen.

Artiodactyla – Bison, Camel, and deer

Bison latifrons – long-horned bison

The long horned bison is represented by several individuals from debris flow, silt, and peat deposits. A partial skeleton of a large bison is known from the peat deposits.

Ovissp. – sheep/goats

A fused radius and ulna and a partially articulated skeleton from Recent deposits at the highest stratigraphic level of Zeigler Reservoir represent domesticated sheep and the onset of the Anthropocene.

Odocoileus sp. – The Snowmass deer

Snowmass deer includes a complete skeleton and isolated elements of younger individuals. The Snowmass deer skeleton from the upper peat represents a 1.5 year old male whose antlers resemble that of a mule deer. However, preliminary investigations of the anatomy of the front leg suggest that the Snowmass deer was larger and had longer toes but shorter forelimbs than O. hemionus. A lower jaw from a fawn comes from the silt above the debris flow.

Camelops sp. – Camels

A single isolated lower molar tooth and phalange indicate a large camel.

Perissodactyla – Horse

Equussp. – Pleistocene horse

An isolated distal metatarsal indicates the presence of a horse from the lowermost debris flow deposits.