Columbian Mammoth, Mastodon Are Stars of Snowmass Fossil Site

Originally posted on August 2, 2011

Excavation work on the largest and most significant Ice Age fossil discovery in Colorado history—now believed to be one of the most prolific mastodon fossil sites in the world—has recently concluded near Snowmass Village. Scientists are now settling in for a comprehensive study of the ancient treasure trove that promises to dramatically expand understanding of Ice Age fauna, flora and ecosystems in the Rocky Mountains.

"While much of our activity has centered around salvaging fossils from the core of the dam site, we are now entering a phase of intense scientific investigation about the origin of the ice age lake and its history," said Dr. Kirk Johnson, the leader of the excavation team and vice president of the Research and Collections Division at the Denver Museum of Nature and Science (DMNS).

The huge cache of prehistoric animal bones and plant specimens was discovered at the Ziegler Reservoir near Snowmass Village last October by bulldozer operator Jesse Steele. Construction workers had only set out to expand the reservoir, but when Steele’s bulldozer rolled out the plate-sized vertebra of a Columbian mammoth, the site was handed over to the Denver museum’s team of paleontologists. After a rushed 69 total days of digging (a time limit set by the village government, since construction of the reservoir was scheduled to resume), nearly five thousand bones were recovered, ranging from American mastodons, Columbian mammoth and a giant Jefferson’s ground sloth, to salamanders and otters.

The site has now yielded parts of 30 individual American mastodon specimens, at least 4 Columbian mammoth, a giant Jefferson’s ground sloth (the only specimen ever found in Colorado), giant bison, horse, camel, a small deer-like animal, and 19 types of smaller animals, as well as a wealth of Ice Age plant and insect specimens.

"Skeletons of small animals are quite rare," Dr. Johnson said last November in reference to the small deer-like animal, a species that is yet to be identified. "This is a delicate little fawn-size animal, still in the ground."

According to Denver museum scientists, the juvenile female Columbian mammoth that was the first discovery at the site may be the most complete mammoth specimen yet found at high elevation in Colorado. Scientists are also excited because it is rare to find more than one mammoth at a single site; this is also the first site in Colorado to yield both mammoth and mastodon fossils.

The Jefferson's ground sloth was also a significant discovery. "We were truly excited on site when this thing came out," said Dr. Ian Miller, curator of paleontology at DMNS. The giant ground sloth species living during the Ice Age was an impressive animal, standing up to 12 feet tall and armed with massive claws. "Ours is a little bit smaller than that, but massive, massive sloths were running around in this area about 14,000 years ago," Miller said, also noting that this ground sloth was "a rare animal."

Speaking of the plant specimens discovered at the site, Miller (who is also a paleobotanist) said, "The peat is almost entirely plants. You can actually pull plants right off the mud. And what we’re finding in there are leaves and seeds and pollen, logs, insects and snails.” Miller finds the insects particularly fascinating. “The insects are still iridescent when they come in the peat… It’s really spectacular. You pull the peat apart and you’ll see iridescent greens and reds in the insects."

Aside from the sheer quantity of bones, this site is special for many reasons. The bones are, technically speaking, unfossilized.  This means that they have not been permineralized—had most of their organic matter replaced with minerals—because they were layered between oxygen-free layers of peat, clay and silt.  So instead of being mineral casts of bones, they are fresh, a bit like the bones your dog might dig up in your yard today.  (At least one of the prehistoric elephant tusks recovered is still white after tens of thousands of years.) Scientists hope to be able to actually extract DNA from the bones, which could provide groundbreaking insights into various Ice Age species.

The site is at a high elevation, which is also rare.  Previously, scientists had wondered if fossils found at high altitude sites might be different from those found at lower altitudes, but since so few sites have been found, it is hard to know. The Snowmass discovery will be another step towards working out that mystery.

Finally, layers of bones represent a large scale of time. Some of the Snowmass excavation scientists believe that from the youngest specimen to the oldest specimen, there may be a span of 100,000 years, though others make more modest estimates of 30,000 to 40,000. Either way, the Snowmass site will almost certainly provide an expanded understanding of prehistoric animal and plant species and climate change processes during the Ice Age.

So what happens next? The bones, which were saturated from heavy snow and rain during the excavation, must be cleaned, catalogued, and then dried slowly to avoid deterioration. This process, already underway, may take a year or longer. Then the bones will be intensely studied by a team of Denver museum paleontologists and collaborating scientists.

Sediment cores collected from the ancient lake bed will be catalogued, high resolution scans of in-place fossils will be performed, and the cores will be studied, first by the Denver museum staff, and then moved to the National Lacustrine Core Facility at the University of Minnesota for permanent storage. "Sediment cores are a very important way for us to sample the complete sequence of lake sediments and preserve them for future research," said Dr. Johnson. "They are a critical piece of the science that can be archived and studied for climate information such as temperature changes and drought."

Meanwhile, the Denver Museum of Nature & Science along with the Town of Snowmass Village has opened the Snowmass Ice Age Discovery Center on the Snowmass Mall, where visitors can learn more about the exciting discoveries through creative displays, educational panels, a half size wooden Columbian mammoth sculpture, videos and interactive programming. And in Denver, the DMNS is exhibiting a full giant bison skull from the site; museum visitors can also view some of the bones excavated from the site from behind a long array of windows as scientists work on cleaning and preserving them.

It may take another three or four years to gain a complete picture of what has been discovered, so stay tuned for more news from Snowmass, Colorado and the Denver Museum of Nature and Science.