Diggin' the South Lake Union Mammoth with Biology Grad Dave DeMar!

The Columbian mammoth (Mammathus columbi) is
Washington's state fossil and had tusks up to 15 feet long.
 These mammoths ranged across North America (down to Honduras!)
until the last glacial retreat ~11,000 years ago. Art by Raul Martin. 
      On Tuesday, February 11, 2014, an employee of Transit Plumbing Inc. discovered a Columbian mammoth tusk at a South Lake Union construction site in Seattle. I had heard about its discovery that day but hadn’t given it much thought beyond thinking “you never know when or where fossil discoveries are going to turn up”. The following Thursday at around 8:30 a.m. I received a text message from Dr. Christian Sidor, University of Washington Associate Professor of Biology and Curator of Vertebrate Paleontology at the Burke Museum, asking if I would like to help excavate the mammoth tusk. I immediately responded “Sure!” thinking what an adventure it would be digging up an ice age animal in the middle of a city. Most fossil excavations that I have participated in involve much older deposits such as those from the age of dinosaurs (66 million year plus) and from places like the badlands of Montana and Wyoming. Later that day I met with Dr. Sidor at the Burke Museum along with Burke Museum Fossil Preparator Bruce Crowley and Research Associate of Paleontology Bax Barton to load up tools and collecting materials such as shovels, awls, paint brushes, burlap strips, and plaster before heading to the site to excavate the tusk. Upon arrival at around 3 p.m. we suited up for the construction site excavation by sporting safety vests, goggles, and hard hats. That wasn’t the first time I had worn such apparel while excavating a fossil. In September of 2006, while working for Uinta Paleontological Associates Inc., I helped excavate a Late Jurassic dinosaur bonebed from a pipeline construction site near Laramie, Wyoming. What I hadn’t encountered was the tremendous amount of news coverage the mammoth tusk would generate. Being in the spotlight was a little unnerving for me but luckily I managed to focus on excavating the tusk and by keeping my distance from the news teams as they interviewed Dr. Sidor and the Burke Museum’s Director Dr. Julie Stein.


Chief Preparator Bruce Crowley searches for the end of the tusk.
Photo courtesy of the Burke Museum.
      Our first objective during the excavation was to determine the length of the tusk by exposing its outer margins. We measured its total preserved length at 8.5 feet (2.6 m) which according to Bax is only about half the length of the largest tusks ever found! Dr. Sidor figured that bit of information would satisfy the news reporters during their early interviews until later developments of the dig transpired. As we continued to unearth the mammoth tusk helicopters hovered overhead while children off in the distance from the neighboring day care center yelled “dig it up, dig it up”. The tusk was waterlogged and soft meaning we would have to be even more careful not to damage it during its excavation.  The tusk was surrounded by loose stratified sand and rounded pebbles and cobbles sometimes as large as a softball. Above that coarse sediment was a thick layer of grayish clay which was deposited at the bottom of an ice age lake. As daylight turned to dusk the small ~12 x 12 ft. squared-off pit encompassing the tusk was bathed in light from two bright lamps provided by the construction crew. After shoveling what was likely more than a ton of wet rock from around the tusk we had it fully exposed and on a pedestal. Several zip ties were wrapped around the tusk to help prevent the enamel from delaminating during the drying process. Subsequently, we placed aluminum foil over the tusk and covered it with plaster soaked burlap strips. After the initial two layers of burlap were added we placed several wooden 2x4s at strategic points around the tusk and a final two layers of burlap for additional support. At that point, which was after midnight and approximately nine hours of intense labor, all we could do was wait for the plaster to dry before undercutting the rocky pedestal and flipping the specimen for extraction the following day.

Chris, Dave, Bruce, and Bax pose with their wrapped prize!
Photo courtesy of the Burke Museum.
      On the second and final day of the mammoth tusk excavation, we prepared for what we had hoped would be a successful extraction of the specimen. Ron Eng, Collections Manager at the Burke Museum, joined us that day at the construction site with a flatbed truck and metal palette for transport of the tusk back to the Burke Museum. Upon our arrival the construction crew and crane operator readied the crane lurking high above for removal of the tusk from out of the ~30 ft. deep pit and onto the flatbed truck. Two of the construction workers attached the palette resting on the flatbed truck to the crane via hooks and rigging and directed it up and over to the smaller pit surrounding the tusk. Once the palette was in place adjacent to the tusk, Dr. Sidor, Bruce, the two construction workers guiding the crane operator, and I readied the palette with blankets for cushioning and extra rigging for securing the tusk to the palette. We also created a makeshift ramp using 2x4s for guiding the tusk up and onto the palette from its pedestalled position. Our biggest concern during the tusk’s removal was that it would break apart as we separated it from its pedestal. Flipping jacketed fossil bones can be tricky as each situation is unique. Given the delicate nature, size, and spiraling shape of the waterlogged tusk we had to act fast yet gentle when flipping the tusk. The last thing we wanted was for the specimen to fall out of the bottom of the jacket, especially under the watchful eyes of the news crews and numerous excited spectators. As we prepared to flip the jacketed tusk, Bruce took the tip end while I took the root end. Dr. Sidor and the two construction workers readied the center of the tusk. On the count of three we swiftly flipped the specimen onto the makeshift ramp and pushed it up and onto the palette with relative ease. Thankfully, our major concern of it coming apart wasn’t realized as the specimen remained intact revealing nicely preserved ivory on its underside. Once the specimen was secured to the palette with a blanket on top for added protection, the palette was fastened to the rigging of the crane and hoisted out of the pit. As it slowly made its way up and out of the pit spectators from all around the construction site began cheering and whistling. Those of us at ground zero shared a sigh of relief and Dr. Sidor and I exchanged a welcomed handshake for its successful extraction. Dr. Sidor soon made his way out of the construction site to watch the tusk’s final descent onto the back of the flatbed truck and to meet the news teams for questions. 

The tusk is hoisted into the air and delivered
to a waiting flatbed truck. Photo courtesy of
the Burke Museum.
      During the two day tusk excavation I also aided Bax in digging an approximately two meter tall vertical trench for sediment samples and description of the lithology (rock types) and stratigraphy (rock layering) of the surrounding rocks. Those collected samples and data are critical for determining the depositional environment (e.g., lake versus stream deposits) that the tusk was buried in and for reconstructing the ancient landscape of the area the mammoth once roamed. To determine what plant types may have been around during the life of the mammoth, Bax and I collected 21 small sediment samples at every 10 cm interval for fossil pollen. We additionally collected bulk sediment from each of those 10 cm intervals for underwater screenwashing and sieving with hopes that at least part of the contemporaneous microfauna and flora was also preserved. We are somewhat optimistic in finding additional components of the microfauna and flora in those samples as we already discovered the fossilized remains of a partial insect carapace (likely a beetle) in the clay deposits of the ancient lake as well as plant debris.  Those samples including the Columbian mammoth tusk are now at the Burke Museum waiting preparation and study and the results hopefully will provide a better understanding of what Seattle was like 10’s of thousands of years ago.

Here are the rest of the Burke's photos, including those with excited children.

A tour of Cretaceous Montana with Dave
      As an added bonus to Dave’s experience at the South Lake Union mammoth site, check out this Jurassic Park themed video he initially created for his family entitled An Adventure 66 Million Years in the Making... Watch while Dave narrates and walks you through his 2012 dissertation research field season in northeastern Montana starting with the Wilson Lab’s base camp at Hell Creek State Park and later in the field in dinosaur-occupied deposits of the Hell Creek Formation. Dave and his field assistant and ex UW Biology student Bashira Chowdhury guide you through their discoveries and collection of the fossilized remains of animals that lived more than 66 million years ago; a time just before the extinction of non-avian dinosaurs and prior to the rise of mammals following the end-Cretaceous mass extinction. The first few minutes of the video are a bit windy but bear with it as the adventures had only just begun. The video is broken into seven major segments with times provided in parentheses for quick access to each major segment and shorter sub-segment:

1) Base Camp: Hell Creek State Park (00:25) and Base Camp Part II (03:01)
2) Preparing to work the From Mars locality (08:50)
3) Crossing Reid Coulee: The way down (10:25), At the bottom (11:47), and The other side (12:47)
4) The Journey to From Mars Parts I-V: Navigating the Landscape (13:52), Fossil Clams (15:00), Fossil Turtle (15:33), The Hill (16:40), and The Locality (17:34)
5) CMM & JPC Localities (19:55)
6) Kafir Locality (21:52)
7) Breakfast at Base Camp and Finale (23:57) and End Credits (24:58)



Comments

  1. Great story Dave! I enjoyed prospecting with you at the Dig School in Hell Creek last summer. Your knowledge and experience was invaluable to me.

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