One of the National Museum of Natural History's responsibilities as a repository for the National Fossil Collections is ensuring that the fossils are preserved, in excellent condition, for future scientific study. But without special care, fossils tend to break over time. Not only are there stresses from being picked up and moved around, but gravity takes a natural toll on heavy, rigid, irregularly shaped objects such as fossils. An earlier post described our work in FossiLab to rehouse our fossil crocodilians in supportive storage trays designed to reduce such damage. Last month, the volunteers finished the crocs and began to rehouse the Museum's type collection of fossil marine mammals. "Type" collections are especially important because they include the fossils on which scientists based the naming and detailed descriptions of new species. Because subsequent discoveries must be compared to type specimens to determine if they are new to science or simply new specimens of known species, there is high demand for access to type collections. This increases both the potential for damage from "wear and tear" and the need to keep the specimens in excellent repair. The photos in this post show some our strategies for achieving both goals. Click photos to zoom.
The lower jaw of a primitive dolphin, Simocetus rayi (USNM 256517), shown above, left, is about 30 million years old. In its new tray, the bone makes contact with the foam beneath it, but the delicate teeth rest on a pillow of batting. This prevents the teeth from shouldering any of the weight of the surrounding bone and reduces the chance they will break. The finger-sized cutouts to the left guide researchers wishing to lift the jaw to grasp it at a safe distance from the teeth. We incorporate "behavior guides" like this into the housing for most specimens. Even the robust vertebra, shown above right, from Basilotritus wardii (USNM 310633), a primitive whale, could be damaged if picked up by the relatively delicate transverse processes (the winglike structures extending from the left and right sides), so we guide the hands elsewhere.
Above left, a volunteer compares bones from the shark toothed dolphin Squalodon whitmorei (USNM 183023) to the photos in the scientific article in which it originally was described. Checking the bones against the illustrations lets us know if any of them have broken during their years in storage. If pieces are missing, we find and reattach them with adhesive. Specimens often include small bone fragments that were found alongside the larger bones, and we check these for pieces that go together, as well. It's surprising how often we find a match (already, through the years, the pieces have been looked over by many sets of eyes) but we are very good at jigsaw puzzles. To the right, above, repaired and rehoused vertebrae of Squalodon calvertensis (USNM 10484) are laid out neatly in a new storage tray.
While all of the fossils in the type collections are scientifically important, some of them are particularly awe inspiring. The three bones to the right are the paired pelvic bones and a femur (upper leg bone) of Basilosaurus cetoides (USNM 12261), a primitive whale that lived about 40 million years ago. Whales evolved from 4-legged animals that lived on land, and as they adapted to life in the water, their hind limbs became small and lost their original function. In the sketch below, taken from an early 20th century publication, you can see these bones in the context of the full skeleton, about half the distance between the ribs and the tip of the tail. The specimen is about 17 meters (55 feet) long, overall, but the diminutive femur measures only about 20 cm (8 inches) in length! When the rest of our skeletal mount of Basilosaurus was put on display in the Sant Ocean Hall, our scientists decided to keep these bones in the relative safety of our collections, replacing them with replicas made from the hind limbs of another specimen.
Follow these links to read more about our specimen of Basilosaurus and visit the Historical Art Gallery of the Department of Paleobiology to learn about the historic scientific illustrations that also are in our care.