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.
External Armature Mounts:
When displaying fossils in an exhibit, how can a balance be achieved between exposing surfaces for viewing, and at the same time supporting the specimen to prevent damage? One method developed to address this problem is the external armature mount. Metal rods are bent to conform to the contours of a specimen, and brackets or adhesives secure the specimen to the support structure. External armature mounting techniques have been refined over the years and are now the preferred method of exhibiting fossil specimens. Major and unique advantages of external armature mounts are that they protect the fossils from the types of damage described in my earlier posts, and improve accessibility for research on the displayed specimens.
| Two examples of external armature mounts previously exhibited in the National Museum of Natural History’s Fossil Hall were mounts of Orohippus pumilus, an extinct member of the horse family, shown above, left, and the dinosaur Diplodocus longus, shown above, right. These specimens are among the smallest and the largest fossil mounts, respectively, that were displayed in the hall. The armature map for Orohippus shows the location of armature used to construct the mount. Armature labeled as ‘internal’ (red in color) is not drilled through bone, as shown in earlier examples, but passes either through the natural openings in the vertebral spinal column, or through sculpted pieces in the sternum and tail. The ‘bolts’ marked in light blue also pass through a sculpted portion of the skull’s palate. With this configuration of support, no fossil material was damaged to produce the mount. Click photos to enlarge. | |
The larger a fossil mount gets, the heavier both the specimen and its armature become. The mounts of Orohippus pumilus (USNM V26305, built circa 1958) and Diplodocus longus (USNM V10865, built circa 1930) offer good comparisons between mounts for lighter and heavier specimens.
| Left: the partially disassembled hind limbs of Orohippus pumilus. The brass armature follows the contours of the bones along the back and inside of each limb, reducing the visibility of the armature when the mount was viewed from the side. Because the fossils are small and light in weight, they could be adhered directly to the metal supports without additional hardware. Right: the partially dismantled Diplodocus longus, showing armature for the limbs and ribcage exposed. The heavier bones of Diplodocus required more substantial support, in the form of steel armature and multiple vertical support poles along the mid-line of the skeleton. Brackets, bolted to the main supports, clasped each bone in place. Click photos to enlarge. | |
| Left: The pelvis of Orohippus, viewed from the underside, with the armature for the hind limbs and tail trimmed away. The appearance of the armature was originally disguised by painting the metal to match the bone color and using a tinted papier-mâché-like mixture to fill and blend between the edges of the metal and the adjacent bone. This mixture had to be removed during the disassembly of the mount, to better understand where the armature was located. Right: the pelvis of Diplodocus, viewed from the rear. A vertical support pole positioned between the descending ischia and pubes bones meets the central horizontal support for the vertebrae. Much of the armature for the pelvis and the hind limbs is tied in to this junction. As with Orohippus, the armature of Diplodocus was also painted to match the color of the bone. Click photos to enlarge. | |
In modern external armature mounts, archival-quality coatings are applied to the metal frame to prevent corrosion and chemical interaction with fossils and the exhibit environment. Padding is used wherever contact could occur between fossil and metal, to prevent damage. Another innovation is the use of removable brackets, which allow individual bones to be taken from the mount, while the rest of the skeleton remains independently supported. This ensures that researchers can access all parts of the specimen for scientific study without disrupting the overall display.
| Two examples of modern external armature mounts. Left: the sternum of a fossil whale, Basilosaurus cetoides (USNM V4675 and V12261), on exhibit in the NMNH Sant Ocean Hall. Small screws allow the brackets to be disassembled, providing access to individual bones. Right: a sneak peek at a specimen to debut in the renovated Fossil Hall when it opens in 2019: the “Nation’s Tyrannosaurus rex”. This photo of the mount’s tail shows the complex bracketing (prior to being coated) custom made for each vertebra, cradling them in place just as a setting would hold a gem in a piece of jewelry. Click photos to enlarge. | |
Over the century-plus history of the NMNH fossil displays, the worth of external armature mounts has been proven in many aspects. The majority of full skeletal mounts from the old Fossil Halls that are returning to display have been completely dismantled, and new external armatures are being crafted for them. This allows for great flexibility in terms of designing the new exhibit and presenting these creatures in lifelike and dynamic positions. It also ensures the specimens will be protected and remain scientifically useful throughout their next chapter of public exhibition. We look forward to previewing more specimens and their mounts as work on the new Fossil Hall continues!
All photos by the author except the Diplodocus full mount photo by Jim DiLoreto/NMNH Imaging and the T. rex tail photo by Steve Jabo
Follow these links to read the first and second posts in this series.