Fossil whales provide the field researcher with a number of challenges. First and foremost, as the name whale implies, the skulls of extant and fossil mysticetes are very large. Even a small mysticete has a skull that is at least several feet long and wide. At the other end of the spectrum are skulls of large balaenopterid mysticetes, or rorquals (this family includes humpback, blue, fin, and minke whales), which can measure upwards of 8-10 feet long.
Additionally, fossil mysticetes are typically encountered in coastal exposures, as marine sediments are frequently deposited along continental margins. The removal of large plaster jackets from coastal areas is a particularly daunting task, especially if it is a rocky shoreline. Wide, sandy beaches pose much less of a problem, and can be towed on a sled or simply placed in a vehicle with low pressure tires.
Here are a couple examples of mysticete crania that I have excavated from the coast in central California, illustrating some of the challenges encountered.Unidentified Balaenopterid Excavation: August 2005
(Coming soon)Herpetocetus bramblei Excavation: June 2007
In June 2007 I found a partial whale skull exposed in this cliff. Part of a small point had collapsed, and in the fracture where the boulders broke away, a cross-section right through the rostrum (nose) of the skull was exposed (red arrow). I found a related chunk of sandstone with a large portion of the rostrum intact. I prepared this, and based on the configuration of the bones in that block, reasoned that the braincase and posterior portion of the skull was in the cliff, intact. Fortunately, I was right.
This is all that was visible at the time of discovery. The V-shaped bone in the middle of the photograph is the vomer, which is shaped somewhat like a canoe in baleen whales; this was slam-dunk proof that this was a whale skull. The cranium is in a shell bed, likely deposited during an ancient storm.
After discovery, the next task was to excavate the skull. This entailed removing overburden (what the railroad pick is for), careful removal of sediment to define the limits of the skull (smaller tools), and listening to classic rock (exhibit C, red radio).
A difficult part of this excavation was trenching. Trenching is the method of digging a trench around the fossil so as to leave the fossil in a pedestal of rock that can be easily undercut after a plaster jacket is applied. In many cases a paleontologist has access to other crew members to help dig a bigger hole; I was working solo for three of the four days, and thus had to dig 'blind' - around the back of the pedestal most of the digging was done by touch, rather than sight, since the hole was too small to get in there myself.
The last day I actually got some help, so this was the only day I appeared in any photos. This is basically the same photo as above, just prior to jacketing. (Photo Courtesy Chris Pirrone)
Here you can see how much of a vertical drop we had, and no room to flip any sort of a jacket. That was very challenging/entertaining.
Finally, the pedestal was wrapped in wet toilet paper. Wet toilet paper doesn't behave well, and tends to shred and cling easily. So, I've patented a method which dampens the paper after its on the fossil. Its far easier to do when you're by yourself, or only have toilet paper (paper towels are far superior, as they can be wetted first). Just like little kids pretending to be fountains in a pool (albeit with urine and chlorine saturated pool water), I simply take a mouthful of water from my water bottle, and spout it out of my mouth; this way, I can use both hands still. This is not a problem if there are more than two people, who can hold down the material while another drips water, or uses the mouthpiece/hose of a camelbak.
But that's besides the point. The TP/PT is to provide a barrier between the fossil and the plaster, because plaster is very difficult to remove, from everything, and especially from something hard and brittle.
Plaster jacketing was completed at about 6pm, and the tide was coming in very quickly. Over the next four hours a herculean effort was made to bring the fossil to safety. These were literally the most stressful four hours of my life, which is why I have no photos of this process. The jacket (which weighed well over 250 lbs) was hauled through the surf for about 150 feet, and then carefully lugged up an algae covered set of natural stairs in the rock. Then, the jacket was placed in a floormat from a car (like a hammock), and carried across a 16" wide rock ledge (with a 10 foot drop to the ocean), and then up a series of "surfer's stairs"; this required lifting the jacket to eye level several times, which was no easy feat. Finally, at 10pm, we hoisted the jacket into the back of my car.