Paleontology Lab

Fossil Preparation

Upon arrival back at the museum, fossils collected in the field are brought to the fossil preparation laboratory. Here the specimens are carefully removed from the surrounding rock with a variety of tools such as dental picks and compressed air powered hand tools.

The lab is staffed by museum employees and dedicated volunteers that are currently preparing fossil specimens from the dinosaur project in Big Bend National Park, the fossil fish project in Wyoming and Montana, as well as marine reptile specimens from the Metroplex and dinosaur material from Wyoming.

 

Mounting the Proctor Lake Dinosaur

ABSTRACT

Skeletal mounts using original material are often controversial primarily because of the subsequent inaccessibility of the specimen to the researcher. This problem was considered in planning new fossil mounts at the Museum of Nature and Science and resolved by developing an armature in which individual skeletal elements are removable. Three composite skeletons of a new ornithopod dinosaur are being mounted, each representing a different growth stage in the life history of these animals. The specimens were excavated from the Twin Mountains Formation (Early Cretaceous) near Proctor Lake in Comanche County, Texas, by Southern Methodist University and Tarleton State University.

INTRODUCTION

The technique of mounting fossil vertebrate skeletons so that the individual elements can be removed from the support armature, though not entirely new, has not been fully explored as an exhibit option. Although many mounts have been constructed that can be disassembled in sections (Gilpin, 1959; Barthel, 1966; Madsen, 1973) the American Museum of Natural History is one of the few institutions to have taken full advantage of the removable specimen mount technique (Norell, pers. comm., but also see Bessom, 1963 and Majumdar, 1974). The controversy over displaying real bone would seem to be solved if the fossils are both quickly and easily removable from the armature and completely undamaged during the mounting process. The only advantage in using epoxy and drilling actual bone for a mount is speed and consequently cost. External mounts often require extra space between bones at articulation points to allow for armature, however this is acceptable in dinosaurs, as they possessed a layer of uncalcified cartilage at the epiphyses that is not preserved in fossil specimens (Reid, 1997). Carpenter (1989) and Carpenter et al. (1994) provides a list of common mistakes made in the mounting of fossil vertebrates.

The specimens used in this composite mount were collected in 1985 and 1986 near Proctor Lake, Comanche County, northeast Texas. The locality contained predominantly disarticulated remains of hundreds of individuals ranging from juveniles of about 1m to an estimated adult size of 3 to 3.5m. These herbivorous bipedal dinosaurs from the Early Cretaceous were closely related to Tenontosaurus and the hypsilophodontids (Winkler et al., 1988; Winkler and Murry, 1989; Winkler, pers. comm.). The large number of animals recovered insured that a great percentage of real bone could be used in the mount. Approximately 70% of the skeleton is original material, with much of the remainder consisting of ribs sculpted for strength.

This type of mount was chosen to allow subsequent removal of individual bones for study and to prevent damage during mounting due to drilling or epoxy. Many modern original specimen mounts still employ drilling as a method of concealing the armature (Madsen, 1973), thus eliminating the possibility of future histological studies. In the case of this small individual, drilling the thin bones was not an option, however in the adult it might have been possible. Also, this type of mount is advantageous because disassembly of the skeleton allows easy transport if necessary.

PREPARATION AND MOUNTING

The first of the three skeletons to be mounted was the mid-sized (2m) individual. Due to the high concentration of tiny bones (<1cm; e.g., phalanges, vertebrae, cranial elements), microscope preparation was necessary. Hypodermic needles of various gauges attached to the tips of adhesive bottles helped immensely in exact placement of glue under the microscope. Missing sections of bone were filled in with epoxy putty and then shaped with a Dremel grinder, often before the bone was removed from the matrix block in order to retain stability and initial orientation throughout the process. Paint was added to the epoxy before setting to approximate the fossil tone. Missing bones were fabricated with urethane casts.

A running pose was chosen, with one foot off the ground behind the animal. The small family unit of dinosaurs in the final display will be in an alert state after being startled by a potential predator. The articulations of bones and positioning of the skeleton of this new dinosaur was aided by comparison to some of its close relatives, Hypsilophodon (Galton, 1974) and Tenontosaurus (Forster, 1990). When likened to these animals it was surprising to find that the tail is a full two thirds of the animal's length.

1/8" round steel was used for most of the framework. Initially, armature for the legs was bent from a single rod and the bones mocked up using a hot glue gun, iron rods and clamps. Temporary mounts can also be accomplished using sandbags (Madsen, 1973) or by suspension from cords (Barthel, 1966).

The vertebral armature was then bent to conform to the spinal column. Individual U-shaped cradles created for each vertebra by soldering 19-gauge steel wire to the frame and bending it to contour the bone. Several sections of articulated caudal vertebrae were purposely left unseparated during preparation so that ossified tendons would not be lost. Unfortunately, this meant that the tail had to be kinked at a slightly unnatural angle. All of the bones fit snugly but can be removed by lifting at the appropriate angle. For soldering, a pocket-sized butane torch was useful because of its mobility in hard to reach spots. Corner braces were soldered to the leg and vertebral armatures, which were then attached with a nut and bolt for optional disassembly later. Vertical rods attached to the base and tipped with cradles to support the tail and pectoral girdle were also created with disassembly in mind. Two additional rods, one for each leg, support the entire structure. These rods are set in holes drilled partway through a æ" aluminum base.

The final framework for the femora involves fitting the fourth trochanter into a loop of wire in addition to cradling the distal ends and heads of the femora. The right tibia complex (including the fibula, astragalus and calcaneum) is nearly vertical and must be twisted clockwise to lock into place. The right foot touches the ground and merely rests on the base against the rod. The armatures for the pelvic and pectoral girdles, arms, ribs and skull were each done separately and then attached. Some of the cradles, especially that of the skull, were completed once their supporting rods were soldered into place on the main armature. Most of the skull bones are separate and removable in a specific order. This required the most planning as well as trial and error. The carpals, metacarpals and phalanges of the hands were adhered and cradled as discreet units. The ribcage armatures are removable due to the necessity of accessing elements beneath. The ribs are entirely sculpted due to strength considerations and the lack of complete bones, and are epoxied to the frame. The only real bones that were glued to the armature were the chevrons, as satisfactory cradles could not be created.

The articulated skeleton has illustrated once again the value of assembling a set of bones into a three dimensional animal. Features that are not otherwise obvious can be revealed when the bones are properly articulated. The aforementioned unsuspected length of the tail is a case in point. In addition, the articulation of the skull revealed a much shorter face in this subadult than had been anticipated. As a result, the animal takes on a much different look.

On completion of the skeleton the bones were removed, the armature painted, and a set of assembly/disassembly instructions drawn up for future workers. At this point the fact that the bones are unattached was convenient for another reason. A stop motion video was produced for exhibit and advertising purposes showing the skeleton "building" itself. The completed Proctor Lake specimen is presently on display at the Museum of Nature and Science in a glass case (fig.) until work is completed on the final two skeletons, at which point the diorama scene will be constructed.

ACKNOWLEDGMENTS

IDale Winkler for his assistance during preparation and mounting, and Anthony Fiorillo and Louis Jacobs for their comments and encouragement. Mark Norell for information on the American Museum's mounts. The fossil materials for this project were provided to the Dallas Museum of Natural History through a partnership with Southern Methodist University and the Institute for the Study of Earth and Man. Funding for this project was generously provided by the Honorable Bill Clements.

REFERENCES

Barthel, K. Werner. 1966. Mounting a skeleton of Smilodon californicus BOVARD. Curator. 9(2): 119-124.

Bessom, Leonard. 1963. A technique for mounting skeletons with fiberglass. Curator. 6(3): 231-239.

Carpenter, Kenneth. 1989. Common mistakes in the mounting of fossil skeletons. Journal of Vertebrate Paleontology 9, Supplement to No. 3: p. 15A.

_____, James H. Madsen, and Arnold Lewis. 1994. Mounting of fossil vertebrate skeletons. In Patrick Leiggi and Peter May (Eds.), Vertebrate Paleontological Techniques. New York: Cambridge University Press.

Forster, Catherine A. 1990. The postcranial skeleton of the ornithopod dinosaur Tenontosaurus tilletti. Journal of Vertebrate Paleontology. 10(3): 273-294.

Galton, Peter M. 1974. The ornithischian dinosaur Hypsilophodon from the Wealden of the Isle of Wight. Bulletin of the British Museum (Natural History). 25(1): 1-152.

Gilpin, Orville L. 1959. A free-standing mount of Gorgosaurus. Curator. 2(2): 162-186.

Madsen, James H. 1973. On skinning a dinosaur. Curator. 16: 224-266.

Majumdar, Pranab K. 1974. A free-standing mount of an Indian rhynchosaur. Curator. 17(1): 50-55.

Reid, R. E. H. 1997. How dinosaurs grew. In James O. Farlow and M. K. Brett-Surman (eds.) The Complete Dinosaur. Bloomington & Indianapolis: Indiana University Press

Winkler, Dale A. and Phillip A. Murry. 1989. Paleoecology and hypsilophodontid behavior at the Proctor Lake dinosaur locality (Early Cretaceous), Texas. In James O. Farlow (ed.) Paleobiology of the Dinosaurs. Boulder, Colorado. Geological Society of America Special Paper 238: 55-61.

_____, _____, L. L. Jacobs, W. R. Downs, J. R. Branch, and P. Trundel. 1988. The Proctor Lake dinosaur locality, Lower Cretaceous of Texas. University of Colorado. Hunteria. 2(5): 1-8. Figure. Proctor Lake specimen on display at the Dallas Museum of Natural His-tory.

A poster on the new dinosaur skeletal mount at the Dallas Museum of Natural History was presented at the Society of Vertebrate Paleontology Annual Meeting, 1997:

(Full citation: G. E. Bennett, III. 1997. A skeletal reconstruction of a new subadult ornithopod from the Twin Mountains Formation of Texas using a removable specimen mount. Journal of Vertebrate Paleontology 17(3): 32A.)

A REMOVABLE SPECIMEN MOUNT OF A NEW DINOSAUR FROM TEXAS

George (Geb) E. Bennett, III

Another form of this manuscript has been submitted for publication in Curator.