By Dr. Rowland, Paleontologist & Las Vegas Natural History Museum Lab Manager
Paleontologists often encounter a jumble of fragile fossil bones at an excavation site. Time may be short and the weather may be uncomfortably hot or cold or windy. Rather than trying to extricate and catalog each precious bone under these circumstances, we often decide to simply put a plaster jacket on the whole mess ― similar to a doctor putting a plaster cast on a broken arm ― and bring them into the lab to work on them.
The first step is to excavate around and under the bones as much as possible, ideally leaving them perched on a pedestal of sediment. We then drape the pedestalled bone pile with wet paper towels, to prevent the plaster from coming into contact with the bones. Next we mix plaster-of-Paris powder into a bucket of water. We soak strips of burlap in the white, soupy mixture, and we apply the dripping burlap strips to the bone pile. The burlap provides strength to the jacket. (1) The first image shows a group of UNLV students jacketing mammoth bones in Amargosa Valley. We let the first coat of plaster dry overnight, and then we apply multiple additional coats, with appropriate drying intervals between coats. The final jacket may be half an inch to a full inch thick, which makes it very heavy.
After the final coat is dry, we undercut the pedestal and roll the jacket over onto a make-shift stretcher. Then we carry it to the vehicle and transport it back to the lab. (2) The second image shows LVNHM Collection Manager, Michele Jones, and her son, Evan, working on a small jacket of bison bones from the Museum’s Carson City excavation.
The plaster jacket technique was invented in the 19th century by two famous American paleontologists, Edward Drinker Cope and Charles H. Sternberg. The only thing that has changed since then is the brand of beer we crack open after the last plaster jacket is finally loaded onto the truck.