Displaying objects as heavy, fragile and complicated as large articulated fossil skeletons requires a great deal of engineering and metalworking expertise. We’ve been dismantling historic skeletal mounts as part of the Deep Time exhibit renovation project, and in the process fossil preparators in the Department of Paleobiology and NMNH conservators have learned a lot about the array of fossil mounting techniques used by our predecessors during nearly 150 years of exhibit building. This series of posts, based on a recent presentation by preparator Michelle Pinsdorf, describes different styles of mounting and considers their advantages and disadvantages in terms of aesthetics, specimen conservation, and, for lack of a better word, “convenience” for those of us tasked with taking the mounts apart.
A common technique for displaying both fossil and modern animal skeletons in museums is to set bones into an artificial slab, or plaque. Plaques can be backed to walls or laid down on floors, and provide a means to create a lifelike pose for the featured animal without a lot of metalworking. At the National Museum of Natural History, plaque mounts have proven to be conveniently mobile, shifting positions as displays have been renovated throughout the years. But for all of the aesthetic and practical advantages plaque mounts have in a museum display, there are research and conservation drawbacks that come with burying almost half of the specimen in an artificial slab. They also are a lot of work to dismantle.
A plaque mount that saw more than a century of continuous exhibition in the NMNH Fossil Halls was Ceratosaurus nasicornis (USNM 4735) a theropod dinosaur from the Jurassic Period. USNM 4735 is a holotype specimen – the physical definition for its entire species. Discovered in 1883, it is both the first and most complete skeleton known from its genus. The plaque was large and fragile. Unlike many of the other mounts we’ve worked on, it couldn’t be moved safely to our fossil preparation lab, so we did the first stages of dismantling work within the closed exhibit halls.
|Deinstalled portions of Ceratosaurus await transport from the Fossil Halls to the Vertebrate Preparation Lab. Click photo to enlarge.|
With all of the sections removed from the plaque, the most time consuming part of the dismantling work is now taking place in our Vertebrate Preparation Lab, where we are freeing the bones of Ceratosaurus one by one, and getting the first view of them in more than a century. The vertebrae are particularly delicate, and with interweaving layers of concrete and plaster adhered directly to them, work is slow and often done under magnification. In addition to exposing the embedded sides of the bones, we are treating the display sides to remove old surface coatings, paint, and sculpted restorations.
The holotype specimen of Ceratosaurus is to return to display in the renovated National Fossil Halls in 2019, but in a very different form. We will mold and cast the bones to assemble and display a freestanding full skeleton, while housing the original fossil material safely in our collections. The process of conserving the bones and building this new mount will be lengthy, but also rewarding. Not only will visitors get a more complete view of this interesting dinosaur, but scientists, finally, will be able to study these important bones in their entirety, not just the parts they could previously see.
Photos other than the first, which is from our archives, are by Michelle Pinsdorf and Abby Telfer.
Read the previous post in this series here.