I am given a shot at digging out the fragments and cracking them open in hopes of finding a fossil. This proves to be an exciting and humbling experience. Even after locating a seam to break the rock open, a false strike can cause a break across the bed and the loss of the chance of finding a fossil. In the beginning, I lose more than I win but with time I begin to get the hang of it. Pretty soon the youthful team is encouraging the old-timer along as my specimens return clear leaf and flower fossils, each of which has been hidden from view for 55 million years. I unearth several different specimens, including a “slim,” their nickname for a compound leaf with elongated leaflets, a small compound leaf from a relative of the mimosa tree, and a palm frond. Each of these delicate fragments is a testament to the power of nature to create with an abundance we can only hold in awe. I also find a small fish skeleton showing, Scott tells me, the deposition of the fossils in an ancient pond. Of the plant fossils, the “slim” is a species that is unique to the PETM, seen only in three of the eight fossil plant sites found in this time period. It is in the family of Sapindaceae, which includes the soapberry tree, maples and the golden rain tree. The palm frond and mimosa-like leaf, among others, are signals that during the PETM this area was warm year round, probably with a pronounced dry season, like parts of dry subtropical Mexico or Central America today.
Finding the fossils is exciting and reminds us of a bit of Smithsonian history. Early in the 20th century, the Secretary of the Smithsonian was Charles D. Walcott, an eminent geologist and paleontologist. He is famous as the discoverer of the Burgess Shale in Canada, a deposit containing remarkable numbers and varieties of early marine animal fossils. Scott suggests that my finding a few fossils on this day may be the first time since Secretary Walcott that a Secretary of the Smithsonian has found a fossil.
After review of all of the fossils found for at the quarry, Scott and his crew begin the careful process of wrapping the specimens to protect them during their shipment back to the Smithsonian. The fossils will be delivered to Scott’s laboratory at the Natural History Museum, were they will be meticulously examined and catalogued. They will serve to help in the continuing effort to unravel climatic, vegetational and ecological changes during the PETM.
Picnic Hill Site
Our last site is that being worked by the vertebrate paleontologists under the supervision of Jon Bloch. Jon greets us at the top of the hill overlooking his site and shares two finds of the day’s work—partial jaw bones with teeth intact of two small mammals that lived in the Big Horn Basin during the PETM. The fossils are notable for two reasons: These are mammals that arrived or evolved in North America during the PETM, primitive ancestors of the horse and the pig. Both lineages diversified and became abundant after their arrival near the start of the PETM, but after 50 million years or so, the horse died out in the New World and was not reintroduced until Spanish explorers returned in the 1500s. Both of the mammals were very small, reflecting a trend during the PETM. The horse may have been no larger than a small cat. It seems that during the period of high temperatures in the PETM mammals evolved to smaller sizes to better deal with the needed energy balance between nutrition and growth.
We accompany Jon down to the bottom of the hill where his crew has spread out over the area looking for fossils and other evidence. Where they find a fossil or even a fragment of one, they place a small flag and record the information about the find. The flag is used by a member of the crew who documents the position of the fossil with submeter precision using a GPS system. The location data allow the team to know the precise level from which each specimen comes, a critical element in reconstructing successive changes in the animals through the PETM.
We walk over the site and talk with each of the crew members, a mix of young students and several senior scientists from other institutions who are interested in the work Jon is doing and are pleased to help out. While this site does not produce many large, articulated skeletons, it does yield a multitude of small fragments of bone, joints and teeth, each of which, when added to the larger collection, helps to tell the story of the PETM.
With the day waning, Jon informs the crew it is time to head back to base camp. Even after a long hot day in the sun the crew seems reluctant to leave—one more fossil could be the most important find of the day. At the base camp they will identify and catalogue their finds, and compare and discuss the results of their day’s work with the other teams.
The fieldwork of the day comes to at end at base camp, a location chosen by the team to be central to all of the sites. It is a good spot, on the flank of a hill and protected from the winds, but high enough to afford a beautiful view of the stark surroundings. Every member of the crew stays at the camp, including the senior staff. Scott informs me it helps with expenses, which run about $7 a day per person, and also allows the entire crew to discuss their work into the night. Everyone is tired, but happy about the accomplishments of the day. A rousing stew is prepared for dinner and eaten with relish by all. The sun begins to set behind the hill and the air cools considerably. The softer light of the late afternoon illuminates the hillsides. Prominently in view six miles to the east is North Butte, where Big Red stands out in the light of the setting sun as a reminder of why we are here.