ReBecca Hunt-Foster, Dinosaur National Monument, Colorado and Utah
Matthew Smith, Petrified Forest National Park, Arizona
For many years, visitors to Dinosaur National Monument (DINO) have been able to see a skull of the large carnivorous dinosaur Allosaurus fragilis. This skull, DINO 2560, has most recently been on display in the Quarry Exhibit Hall (QEH) in front of the cast of its skeleton, on the lower level across from the Carnegie Quarry Wall where it was discovered in 1924. It is currently the only real complete dinosaur skull material available for close-up viewing rather than on the quarry wall. The skull is located in the QEH's main exhibit area and is very popular with the 300,000+ yearly visitors to DINO. In 2019, this skull was temporarily removed from exhibit so it could be repaired and stabilized.
DINO and Petrified Forest National Park (PEFO) entered a partnership to support the critically needed preventative conservation of this rare and complete skull. The manner in which the skull was on display was creating stress fractures on the skull and lower jaws where certain small points were carrying their entire weight. Part of the lower jaw had also been removed for research and was unable to be properly reinstalled for exhibit due to the condition of the mount. The jaw had been lying flat within the exhibit case for over a year, which was hard on the specimen because a fossil resting unsupported typically only contacts the exhibit surface at three or four points and thus develops stress fractures.
It was decided through a technical assistance request to take advantage of the fabulous skills and past experience of museum curator Matt Smith at Petrified Forest National Park. Smith supervises a small cadre of seasonal museum support staff and has gained much experience in constructing and fabricating museum exhibits during his 22 years working for the National Park Service. The skull was removed from exhibit in late August of 2019, and the skull of the newest dinosaur named from DINO, Allosaurus jimmadseni, was put on display—a rare treat for visitors and a wonderful substitution. A notable difference between these two species of dinosaur which have both been discovered within the monument is one of geologic age: Allosaurus jimmadseni was discovered in the older Salt Wash Member rocks of the late Jurassic Morrison Formation, and Allosaurus fragilis is known from the younger Brushy Basin Member of the Morrison Formation, where the historic Carnegie Quarry is located.
The Allosaurus fragilis skull (DINO 2560) was transported by DINO Paleontologist ReBecca Hunt-Foster to PEFO for the work to take place. The steel mount for the skull was strengthened with an additional strut to reduce the visible sway and bounce that had been observed while on display at DINO. This should reduce the likelihood of damage over time through vibration due to seismic, construction, or other activities. The padding on the skull mount, which originally was an unknown silicone-like material, was removed and replaced with a form-fitting epoxy “cradle”. The cradle is minimalistic but supports the skull along much of the underside of the palate and robust quadrates (bones that articulate to the lower jaw) while avoiding the delicate bones of the braincase. The cradle is lined with a soft cover of museum-quality felt which adds padding and should last for years while it largely protects the skull from chemical contamination at the points of contact. PEFO museum technician Nicole Dzenowski and intern William Reyes, stabilized small cracks in the skull and lower jaws with Paraloid B-72, an archival adhesive used by art conservators, and larger fractures were filled and stabilized with a mix of B-72 and glass microbeads. Several kinds of historic fillers such as plaster, epoxy putties, and other unknown kinds were documented and painted a neutral grey color to distinguish them from the fossil while standardizing their appearance to avoid distracting the public with their patchwork appearance.
Previously, in order to properly mount the specimen, the skull needed to be slowly lowered into place above the delicate lower jaws subjecting the specimen to an unsafe level of handling risk. One slip and much of the specimen could be badly damaged. Custom felt-lined brass mounts that conform to the lower jaws were fabricated with small removable clips. The clips allow the mandibles to be safely removed and replaced beneath the skull for research purposes while holding them securely in the event of possible seismic activity. All treatments were recorded and can be added to DINO’s archives. A time-lapse video detailing the process should be available in the coming months on the PEFO YouTube channel.
The skull was returned to DINO in mid-November and immediately went back on display. Through this partnership, the skull is now ready for a longer, safer presentation while on display to the public at the Quarry Exhibit Hall.