Preparator Virginia Heisey instructs students in the fossil
of WISE 187..
The Stony Brook vertebrate fossil preparation lab is a state-of-the-art facility. We are equipped to perform fossil preparation on
specimens as small as the inner ear bones of mouse-sized mammals, and as large as sauropod dinosaur limb bones. We also have
the material and technical capabilities for molding and casting
specimens for scientific research or for display. With two fume hoods, three vacuum trunks to filter out ambient dust, and
two sealed work boxes, our lab staff has excellent protection against dust, chemical, and noise pollution. Over the last
several years we have taught a section of a course on fossil lab methodologies to first-year undergraduate students in
Brook Women in Science and Engineering program. We welcome the opportunity to train serious, hard-working
people from all backgrounds as volunteers, and we regularly host a variety of students and visitors interested
in paleontology and fossil preparation.
Fossils from Madagascar awaiting preparation in the lab.
After fossils have been collected in the field, it is not usually possible for paleontologists to study them
immediately. Weathering of bone before it becomes fossilized, geological processes, and erosion of fossilized
bone when it again comes near the surface of the earth all do damage to specimens. Fossils are therefore often
broken, dislocated, and covered with sediment. Preparation is the process by which fossils are cleaned and
repaired. The two general categories of fossil preparation are mechanical and chemical.
A variety of simple tools are used in mechanical fossil preparation.
MECHANICAL PREPARATION utilizes tools that apply
external physical force to sediment (also called matrix) in order to remove it from fossil bone. A whole suite of
tools are used in mechanical prep, from insect pins and dental picks to jackhammers and sandblasters, depending
on the hardness of the matrix and the nature of the preservation of the fossil. Tools such as
airscribes vibrate at hundreds to thousands
of cycles per minute, and shake or chisel matrix from bone. Grinding
tools apply more tangential, frictional forces, usually employing a wheel coated with fine abrasive
grit. The air abrasive uses compressed air to
shoot streams of fine particles, eroding the matrix in much the same way a sandblaster is used in construction.
To see an example, CLICK HERE.
This piece of limestone is probably fossiliferous; the green circle on the top left of
the block marks an area where bone is showing. After several iterations of acid etching, washing, and mechanically
picking away limestone softened by acid, the bone becomes more obvious along the upper edge of the block.
More acid runs begin to reveal the partially intact skeleton of a chipmunk-sized mammal. As matrix is removed,
cracks are filled and bone is supported by cyclododecane, a sublimating hydrocarbon.
CHEMICAL PREPARATION relies on chemical
rather than physical forces to remove matrix from fossils. The most common chemical prep method
is acid etching. Many fossil-bearing rocks are partly or wholly composed of limestone, or
calcium carbonate, which dissolves into carbon dioxide and calcium ions when in the presence
of acids. Highly dilute (3-7%) concentrations of formic or acetic acid in water are most commonly used,
along with a buffer to protect the calcium phosphate that comprises the fossil bone. Two
other less-used forms of chemical preparation are iron reduction and clay disaggregation.
MOLDING AND CASTING
The replication of important fossil materials is often essential to scientific study. Original
specimens can be too fragile to be frequently handled, must sometimes be viewed by multiple
researchers at different institutions, and may need to be returned to a distant, foreign
museum for curation. All these factors make molding and casting important in paleontological
research. Furthermore, public desire to see particularly well-preserved fossil specimens
facilitates the production of replicas for light-weight, dynamic museum displays not
necessarily achievable with fragile originals.
MOLDING is the capture of surface detail on an object. In our prep
lab, this translates into using latex, silicone, or urethane rubbers that can be applied to
and peeled safely away from the surfaces of fossil bones. Molding rubbers are poured
or layered on with a brush; the end result is analogous to a photographic negative, with mold
concavities corresponding to fossil convexities, and vice versa. When the molding material is
too thin to support its own shape, a secondary layer, called an overmold or a mothermold, is
applied in plaster, urethane, or fiberglass-reinforced polyester. To see a slideshow demonstrating
how to mold a simple object, CLICK HERE.
Some molds can be quite complex, requiring many distinct pieces and taking months to complete.
CASTING is the capture of the negative surface detail on a mold
onto a positive surface, thus recreating the size and external detail of the original molded
object. Plaster is sometimes used to fill molds, but more frequently thermoplastic resins such
as epoxy, urethane, or polyester are employed. All of these materials begin as a liquid which,
when catalyzed, hardens into a solid representation of the original molded object. As with
molding, casting materials are sometimes poured and sometimes brushed in thin layers which
are backed with a harder substance. The resins are sometimes tinted, and the final product
can be painted for purposes of research or display.
The two skulls shown here are plastic replicas of original fossil
specimens. The theropod dinosaur Majungatholus (right) and the broad-snouted
crocodile Mahajangasuchus (left) were both cast from constituent skull elements found
in pieces in the field and then re-assembled as they would have appeared in life. The skull for Majungatholus
was virtually complete; Mahajangasuchus had only a partially-preserved skull which needed to be reconstructed in certain places for a
museum-type display. CLICK HERE to see a slide show of that process.
Stony Brook University
Department of Anatomical Sciences
HSC T8 031
Stony Brook, NY 11794
e-mail inquiries: firstname.lastname@example.org