Ancient Mammal Found at SLAC
Discovery Day
On October 2, 1964, excavations were in progress for the Beam Switchyard (center) and Experimental Area (foreground) at SLAC when a "lucky mistake" brought Paleoparadoxia to the surface.
Three narrow beam channels were being excavated above the Beam Switchyard: the B-line leading to the End Station B, the A-line leading to the End Station A, and the central C-line for future experimental use. Thick dirt banks were to remain in place between these channels.
Observers viewing the excavations from an elevated tower watched as two bulldozers passed each other and turned in the B-line channel. Suddenly realizing that only one machine at a time should have been able to fit in that narrow channel, they realized that the channel must have been cut too wide. Hurrying to assess the extent of the error, they paused to take this photograph which shows both the bulldozers' tracks and the change in grade, indicating where the wider cut had been made. SLAC engineers inspecting the erroneous cut immediately noticed a line of dark brown bones, buried about three feet above the base of the sandy yellow bank. The red dot shows where the fossil was found.
Shored Cave Marks Paleoparadoxia Dig Site
| SLAC's construction crews cut and shored the dig-site tunnel for the paleontologists. The tunnel is marked at the red dot in the distance of this photo of the experimental area under construction. |  |
Because the "lucky mistake" had created a wider channel, extra space was provided so that the construction work of the accelerator was able to continue without interruption throughout the removal of the fossil skeleton.
Paleontologists Prepare Fragile Fossil Bones
Dr. Charles Repenning (photo below) and his assistant are shown at work, forming a plaster jacket around the fossil elements so that the fragile pieces could be removed without damage.
After the bone has been cleared of rock from the upper and side surfaces, it is painted a number of times with a thinned solution of a fast-drying glue. The glue penetrates the surface and serves as a hardener. When it is thoroughly dry, the unit to be jacketed is covered with several layers of wet newspaper. While the paper is still wet, strips of burlap soaked in wet plaster of Paris are laid over the paper, gradually forming a complete cover over the top and around all sides of the exposed bone.
When this jacket is dry and hard, the rock in which the fossil is still embedded is carefully cut away to such a depth that the complete fossil unit can be lifted out and turned over, still protected by the rock matrix. If further protection of the fossil seems desirable, a second plaster jacket covering can be made to cover the newly exposed surfaces. All of this jacketing equipment, plaster, burlap, newspaper, buckets, glue, even water, must be transported to a dig site.
 |
The bones exposed in this photo are the left femur, preserved articulated in the socket of the pelvis, also in view. |
Near them is the sacrum, already undergoing the jacketing process. Repenning is applying the glue solution while his assistant clears away more of the sandstone matrix between the bones.
Uncovering and Collecting Fossil Bones
|
In this photograph, Adele Panofsky clears the sediment from the lower end of the spine. The complete column was preserved in articulation with the ribs, all the way from behind the neck to the end of the tail. |
 |
After clearing away the surrounding rock, the fossil bones were removed individually, or in convenient smaller assemblages to the paleontology laboratory of USGS, Menlo Park. In the photo above, you can see that the ribs were being collected in shorter sections, six at a time. The articulating ends of the right ribs are still in place. The rear elements had not yet been uncovered. Further excavation of the cave and timber-shoring would be done before the dig could be completed.
