Key Points:
•In order for fossils to be part of our scientific database, they need to be collected from the field and stored and studied in a collection.
•Discovery of fossils in the field requires actively searching likely deposits and careful excavation of bones.
•Steps must be taken to recover the fossils and get them safely to a collection.
•In a museum specimens are prepared: sediment is removed and the bones protected.
•The majority of fossil specimens accessioned into a collection are intended for research purposes, and are not shown on display to the public.
•If the specimens are intended for display, preparation often involves restoring missing fragments of a bone. If they are intended to be mounted as a skeleton, missing bones must be created (by mirror-imaging bones from the other side, or by duplicating from other individuals) and an armature framework constructed to support the whole structure.
Step 1: Finding the Fossils (Prospecting)
In order for a fossil to be useful in paleontology, we have to know it exists! That means someone has to find it in the field, recover it, and bring it back to a lab or museum for description and study.
Many fossils are discovered purely by accident, by individuals not looking for fossils at all. They are found by people digging foundations for buildings, or quarrying rocks, and then brought to the attention of scientists. However, for the most part paleontologists actively seek out new specimens. These might be elaborate expeditions, short day trips, or any scale in between. The team might be a few individuals, to a dozen, to many hundreds (although the latter cases tend to have been rare in history.) (One important aspect, though, is that one should never go out in the field alone (or at least out of communication!)
In order to find dinosaur fossils, you have to go to rocks of the right geologic age and depositional environment. (Some dinosaur specimens do wind up in marine units, but these are relatively scarce. It is more cost effective to have people come across these by accident (or possibly searching for marine fossils) than to organize dinosaur fossil hunting expeditions aimed at marine formations.
While in the field, prospecting works by walking the hills of the badlands and looking for fragments of bones and teeth weathering out of the sediment. Normally you don't immediately find a bone sticking out of the ground: instead, one looks for a trail of fragments weathering out of the hillside, then trace them up to the layer in which they are coming.
If you determine a layer in which fossils are preserved, you move from prospecting to excavating.
When you come across a layer with fossils, it is unlikely that it is the current surface of the ground. (In fact, if that were the case, the fossils would have weathered into fragments!) So some degree of removal of the sediment above the fossil layer (the overburden) has to be done. Depending on the geometry of the situation, this might involve geologic hammers, picks, shovels, pneumatic drills, jackhammers, backhoes, or (in the old days) dynamite. Ideally one wants to expose a broad surface parallel to the bedding plane with the specimens.
Once the area immediately above the fossil is exposed, the team will dig downward onto the fossil layer. ("Digging" here really should be "scraping": when you are close to the bones you use awls and dental picks, not shovels and rock hammers, for fear of obliterating the very specimens you want to collect.) Each person on the team works in their own part of the quarry, working downward to expose the upper part of the bones (if any) they come across.
As bones are exposed, they need to be protected. Permineralized bone may be dense, but it is fragile and subject to shattering. Often a consolident (generally some plastic mixed with acetone) is "painted" or dripped onto the specimen: the mixture penetrates the fossil and enters the pore space, then the plastic is left behind as the acetone quickly evaporates. This helps to hold the specimen together and makes it more resilient.
The quarry site is mapped as the bone layer is exposed. This information is important to help reconstruct the taphonomic setting of the layer, which will help in reconstruction what happened to the bones between the death of the individual(s) and their burial. If nothing else, it is important to figure out which bones go with which individuals!
Little Things Count, Too: Microsites Large dinosaur bones tend to get the majority of attention. But a substantial amount of fossil data can come from isolated teeth and the bones of small animals. Fossil localities in which these are concentrated are called (not too creatively) microsites. The procedures to collect these are different from those of larger skeletons. In many cases the paleontologist may bulk sample (i.e., just dig up a bunch of) sediment, then sieve the material through metal screens of different mesh widths; in others they might just be picked up off the surface. (In both cases these can benefit from a lot of people working together.) The fossils can then be collected and catalogued. Microsites have many beneficial aspects: for instance, they are likely to more accurately preserve the biodiversity of a region. (Consider how much more of an environment is made up of songbirds and rodents than big predators and prey.) On the flip side, their specimens are essentially always disarticulated, so our knowledge of new species collected in this fashion does not include what the whole animal looked like.
Footprints in the Field: While in many body fossils the physical substance of the bones and teeth are the key information, that isn't always the case for body fossils. For footprints in particular it is the shape and position of the imprints which is generally more important. This is especially true for footprint sites that might cover many hectares: it would be impossible to physically collect all these tracks!! Various forms of GIS (geographic information systems) are used to record the position of the tracks in 3D space; high quality photographs, 3D photogrammetry, lidar (laser-scanning), and other techniques are used to digitally preserve the features of the individual tracks.
Smaller bones and teeth might be wrapped up with paper towels and/or foil, requiring no additional protection. These can be carried back to the field vehicle as is. But larger bones--or sets of bones still in articulation--require special care. A very standard technique in field paleontology is jacketing. The upper surface of the bone is exposed, then a short margin of sediment around the bone is traced. The field workers move downwards until the bone is on top of a short pillar of sediment. When they are underneath the bone layer, the whole area is cleaned off. Some sort of separator (in the 19th Century it was wet rice paper, but for the last century or more the go-to material has been wet toilet paper) is put on to cover the surface, then a layer or two of plaster and burlap is laid over this and left to dry. The team then undercuts the pillar and as carefully as possible (often praying to Lethaia, the goddess of field paleontology, or any other imaginary supernatural help they can think of) tip the pillar over and hope that the whole block doesn't fall apart. On the newly-exposed undersurface the work starts again, carefully working the way down to close to the bone layer. A new cover of separator and plaster is put on the lower side, so that the whole bone and some surrounding sediment is jacketed. These jacketed blocks (whose positions should have been carefully mapped up at the beginning of the process) then can be carried back to the vehicles.
As a field season (running from a week or two to most of the summer, but normally around a month) progresses, it is almost certainly the case that many individual sites and quarries will be worked by a team. All the appropriate data has to be collected for each site: its sedimentology, sedimentary structures, statigraphic level, specimen maps, etc. All specimens have to be carefully labels so which site they are from and where in the site they come from can be reconstructed.
At the end of a field season the specimens need to be shipped back to the museum in which they will be studied. By muscle power (or sledge or helicopter) the bags or bones and jackets are moved to the off-road vehicles, then driven back (or shipped via some other transport) to a lab.
Back at a laboratory the field specimens need to be prepared before they can be stored and studied. Some require very little work: often teeth need very little cleaning or repairs, for instance. But in many cases there is a substantial amount of work required, done by a special group of technical paleontologists called preparators.
Specimens in jackets can be stored in these until they are ready for preparation. (In fact, there are jackets from the 19th Century Yale field expeditions still unopened in the collections of the Peabody Museum!) But since most paleontologists actually want to study the bones that they found, jacketed specimens need to be removed from their jackets. This is done in a preparation lab. These have appropriate tables, lighting, HVAC and other air handling equipment, and especially cutting, drilling, and scribing devices. Preparators carefully open the jacket and excavate the bones from the sediment. They will often be applying special consolidents and other protectors on it the bone.
There may be more serious repairs required: gluing together broken pieces, for instance. Larger specimens need a new sort of jacket: a storage jacket, to protect them while they are in cabinets and shelves.
Copying Fossils: Casts: Another task that preparators have to do is duplicating fossils. This is the process of casting, an artificial equivalent to natural casts. This is done so that copies of the fossil can be shared with other researchers, used for display at other museums, brought to classrooms and other scientific outreach, and possibly for mounted specimens. Molds are made so that many plastic casts can be made.
Every specimen in a museum has to have a record; otherwise they are useless as data. So museums have catalogues listing each specimen, its identity, the site and formation it was from, who found it and when, etc. This process is called accessioning, and is the way a bone or tooth makes its way into the scientific record.
Specimen Numbers & Museum Abbreviations: Each fossil specimen accessioned in a museum has a particular code--a specimen number. This allows researchers to go back to the same specimen to attempt to replicate the observations of previous workers. Each specimen number consists of a museum abbreviation (representing the institution and collection in which the specimen is maintained) and a unique number associated with that specimen (different institutions have different algorithms for this; some simply list specimens sequentially in the order they were accessioned; others with codes that combine the year of discovery and other information.)
There is no way (or reason) for you to memorize all the various museum abbreviations. In fact, any paper which discusses particular specimens is obliged to have a table or paragraph listing the institutional abbreviations used in that particular paper. Here is a crowd-sourcing attempt to create an online list for vertebrate paleontological collections. But just to give some examples of ones you are likely to commonly encounter in this course:
American Institutions: AMNH: American Museum of Natural History, New York, NY; CM, Carnegie Museum of Natural History, Pittsburgh, PA; CMNH, Cleveland Museum of Natural History, Cleveland, OH; DINO (formerly DNM), Dinosaur National Monument, UT; FMNH, Field Museum of Natural History, Chicago, IL; LACM, Natural History Museum of Los Angeles County, Los Angeles, CA; MCZ, Museum of Comparative Zoology, Harvard University, Cambridge, MA; MNA, Museum of Northern Arizona, Flagstaff, AZ; MOR, Museum of the Rockies, Montana State University, Bozeman, MT; SDSM, Museum of Geology, South Dakota School of Mines and Technology, Rapid City, SD; TMM, Texas Memorial Museum, University of Texas, Austin, TX; UCMP, University of California Museum of Paleontology, Berkeley, CA; USNM, National Museum of Natural History, Smithsonian Institution (formerly the United States National Museum, hence the acronym), Washington, DC; YPM, Yale Peabody Museum of Natural History, Yale University, New Haven, CT
Canadian Institutions: CMN (formerly NMC), Canadian Museum of Nature, Ottawa, ON; ROM, Royal Ontario Museum, Toronto, ON; RTMP (sometimes TMP), Royal Tyrrell Museum of Palaeontology, Drumheller, AB
A Smattering of Other Institutions from Around the Globe: GI PST Institute of Geology, Section of Paleontology and Stratigraphy, Mongolian Academy of Sciences, Ulaanbaatar, Mongolia; IVPP, Institute for Vertebrate Paleontology and Paleoanthropology, Beijing, China; MACN, Museo Argentino de Ciencias Naturales 'Bernardino Rivadavia', Buenos Aires, Argentina; MfN (formerly HMN), Museum für Naturkunde Berlin (formerly the Humboldt Museum für Naturkunde), Berlin, Germany; MNHN, Muséum National d'Histoire Naturelle, Paris, France; MUCPv, Museo de Geologia y Paleontologia de la Universidad Nacional del Comahue, Neuquén, Argentina; NHM (also NHMUK, formerly BMNH), Natural History Museum (formerly the British Museum of Natural History), London, UK; PIN, Paleontological Institute, Russian Academy of Sciences, Moscow, Russia; SAM, Iziko South African Museum, Capetown, South Africa; ZPAL, Institute of Paleobiology, Polish Academy of Sciences, Warsaw, Poland
Museums behind the scenes have collection rooms where fossils are stacked on shelves or in cabinets. A staff of collection managers is responsible for maintaining these, and making them accessible to visiting researchers. (Despite common thoughts to the contrary, this is a different job than curator, which is normally a research-oriented position.)
The vast majority of fossils in any museum will mostly be in storage, and be worked on by researchers but not seen by the general public. But a number of skeletons and other specimens might be selected for public display. These are chosen for a number of reason: most importantly how impressive they might be and how they might be incorporated thematically into a larger exhibit.
Complete fossil skeletons are vanishing rare, however, especially for larger species. Broken bones need to be repaired, for instance, and missing bones need to be replaced. In the case of missing bones, they might be sculpted (or today, 3D printed) by mirror-imaging the same bone from the opposite side of the body. In other cases it might be replaced by the same bone from another individual (but care must be taken to make sure the proportions are appropriate for the main skeleton). Some museums make it clear (by color, for instance) which parts of a restored fossil are real, and which are filled in; in others, though, it is hard to tell.
The bones are arranged on an armature to hold them together (since skeletons do not stand up by themselves!) Museum technicians these days construct such armatures to allow individual bones to be removed and studied, but in the older times they would actually drill right through the bones and run metal piping through them! As a consequence, older museums often have programs trying to repair and restore fossil displays from the 19th and 20th Centuries. This is a long and costly process, though, so in some cases the old-style mounted skeletons remain as-is.
Not every fossil skeleton on display at a museum is actually the "real" thing, though. Many museums have at least some skeletons which are entirely casts, based on specimens at other museums. However, claims that museums are trying to dupe people are totally unfounded: simply reading the museum display sign for that specimen should make it clear if it is the original or a cast!!
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