GIANT SLOTH FOSSILS

The giant sloth pelvis has been preserved for 25-45,000 years in the Los Angeles labrea tar pits. Scientists have spent more than a century excavating and cleaning fossils from this area, which helps fill in gaps on a 50,000 year timeline of life in the region. We went to the la brea tar pits to see how specimens are discovered, cleaned, and pieced together to build that record.

The process of excavating specimens from the La Brea Tar Pits begins with a sticky scavenger hunt. There are around 130 pits at the tar pits, which is technically a misnomer since they don't produce tar anymore.

We don't have pits the way we actually do, which is with asphalt. Some tarpits are still connected to their oil source, like this one. Right now, I'm in Pit 91. That was the 91st pit I know about. Others become disconnected from their oil source and dry out huge chunks of the deposit. Box 13 contains tens of thousands of fossils. The excavation process isn't as simple as just pulling a bone out of some goo. Sometimes I find a fossil and excavate it out in 15 minutes. Other times, I'm looking at a fossil for several months, and it's still not easy to get it out!

In order to begin our search, Laura first sets up a makeshift grid. This will help Laura keep track of where and in what position fossils are found since the asphalt is too dense for traditional radar to provide initial images. Take this sabretooth cat skull, which has been weeks in the making. Based on 16 years of experience, laura can estimate how many fossils are in a given deposit. After applying some elbow grease and eyes, she starts the painstaking task of carefully cutting the skull out of the matrix that surrounds it.

This is where it gets tricky: if I'm certain that I won't find any fossils, I'll have tools like hammers and chisels that will allow me to reach in and remove some of those items. Asphalt serves to both protect the organic matter surrounding the fossils and make them more delicate than traditional stone fossils. To begin, I'll use very small tools like this dental pick, which I obtained from local dentists. At times, I'll use it like a dentist would, sometimes more like a clay sculpting tool to remove sediment from the fossils. At other times, you'll see me using a paintbrush with natural bristles to preserve not only the delicate bones but also the matrix itself.

We will thus pour that chemical solvent—a novak 73de, which is a chemical degreaser into that area. The solvent dissolves the asphalt and leaves behind treasures. This fossil, which is the end of a tibiotarsus, is larger than a chicken, and we also have plant fossils. After the matrix is gathered and the surrounding sediment is removed, I should be able to carefully remove the fossil from its tangle and send it to the lab, where experts will spend even more time crafting this one masticated skull.I would say that this could probably take me up to 10 hours in total to complete.

Since the firm tip applicators don't grip fibers and cause harm to the fossil by transferring too much fiber onto it, we like to use them in regions where exposed bone is jagged. It pretty much works like painting. Our goal is not to thoroughly clean the specimen; rather, it is to prevent deterioration over time, so some debris remains behind. We leave the internal matrix in the skull because it provides structural support and stability. The asphalt permanently stains the fossil a deep brown color. If a fossil is damaged or comes out of the pit in pieces it can be fixed.