"Zed" is our newly discovered Columbian mammoth, and the most complete mammoth skeleton we've ever found.
What have we unearthed this week? How's the preparation of Zed, the Columbian mammoth, going? Do the excavators ever wash their clothes?
For answers to these questions and many more, please check out our frequently updated excavation blog, The Excavatrix.
In June of 2006, the Los Angeles County Museum of Art (LACMA) began work on a new underground parking garage. During the course of construction, 16 new fossil deposits were discovered, including the semi-articulated, largely complete skeleton of an adult mammoth. Rather than halting construction, paleontologists at the Page Museum worked with the team that was mitigating the fossil resources to build large wooden “tree” boxes around each deposit. Some of the larger deposits were split into more than one box, eventually resulting in the 23 fossil blocks that "Project 23" is named for. In 2008, the boxes were moved by crane and truck to their present location immediately north of the Pit 91 complex, and excavation began. In addition to the 23 tree boxes, there were also some 327 buckets of fossil material recovered from the LACMA salvage site for paleontologists to clean and sort through.
The boxes are on view to the public, with excavators working seven days a week to recover all the fossils. As with Pit 91, excavators use small hand tools such as dental picks, chisels, hammers, and brushes to remove the matrix (dirt) surrounding the bones. This matrix is kept and will be cleaned at a later date and eventually sorted for microfossils in the lab. Unlike Pit 91 however, excavators sometimes use pneumatic power tools in areas where there is less bone and harder asphalt. Additionally, our measurement system has changed slightly. We now use the metric system rather than Imperial: each deposit is divided into one meter square grids, and each grid is taken down 25 cm at a time. Larger, more complete bones are "measured out" of the grids according the same system developed for Pit 91, whereas bone fragments and plant material are placed into separate containers for bulk cleaning. This speeds up excavation considerably without sacrificing taphonomic data (taphonomy is the study of how fossil assemblages form). By carefully mapping and photographing the fossils as they are found within the grids, we are learning how the pits formed and how the animals may have become trapped.
Excavators typically work on several boxed deposits at any given time. Each deposit is quite different in its geology and fossil content. It is also likely that each deposit was formed and trapped animals at different times. Deposit 1 has already proven itself markedly different from Pit 91. The main fossil deposit is concentrated in only two grids in the southeast corner of the box, and surrounded by incredibly hard asphaltic sediment. Thus far, approximately 75 percent of the deposit has been devoid of the large jumbles of bones typically associated with Rancho La Brea. However, we have found an immense number of invertebrate and plant fossils, including articulated millipedes, large layers of oak leaf litter — in some cases large enough to traverse multiple grids — and a wide variety of shells. Furthermore, excavators have noted a surprisingly high amount of "pit wear" on the fossils — smooth grooves and rivulets caused by bone-on-bone friction. Though pit wear is unique to Rancho La Brea, we are still not sure what forces the bones to rub against each other in the first place. The large number of strangely worn bones coming out of Deposit 1 gives us an exciting opportunity to further study this phenomenon in situ.
For an in depth look at what excavators have dug up this week, please visit their blog, "The Excavatrix!" It's updated about once a week (time permitting) and is filled with photos and video.