Fossil preparation

Last updated December 04, 2024

Fossil preparation is a complex of tasks that can include excavating, revealing, conserving, and replicating the ancient remains and traces of organisms. It is an integral part of the science of paleontology, of museum exhibition, and the preservation of fossils held in the public trust. It involves a wide variety of techniques, from the mechanical to the chemical, depending upon the qualities of the specimen being prepared and the goals of the effort. Fossil preparation may be executed by scientists, students or collections personnel, but is often undertaken by professional fossil preparators.^[1]

Techniques

Acid maceration

Acid maceration is a technique to extract organic microfossils from a surrounding rock matrix using acid. Hydrochloric acid or acetic acid may be used to extract phosphatic fossils, such as the small shelly fossils, from a carbonate matrix. Hydrofluoric acid is also used in acid macerations to extract organic fossils from silicate rocks. Fossiliferous rock may be immersed directly into the acid, or a cellulose nitrate film may be applied (dissolved in amyl acetate), which adheres to the organic component and allows the rock to be dissolved around it.^[2]

Film pull

The film pull technique is a means of recovering carbonaceous compression fossils for study under transmitted light microscopy. An acid is applied to the surface of the rock to etch away the matrix from the surface, leaving carbonaceous tissue protruding. (Surfaces not to be etched can be coated in a wax (e.g. Vaseline or grease). This is usually accomplished by placing the rock upside-down in a weak, continually stirred acid, so that any debris can be washed away. Nitrocellulose is then painted on to the fossil-bearing surface, and once dry may be peeled from the rock, or the rock dissolved in hydrofluoric acid.^[3]

The method was pioneered by John Walton, in collaboration with Reitze Gerben Koopmans, in 1928 as a method to derive serial thin-sections without the time, expense and lost material incurred by dissolving the rock.^[4] An improvement on the method, using gelatine (with glycerin and formalin) instead of cellulose, was reported in 1930, and is especially suitable for larger samples.^[5] This solution-based method was largely superseded by the use of pre-formed sheets of film, similar to those used in overhead transparencies; cellulose nitrate and cellulose acetate can be used, although the latter is preferable.^[6] By wetting the reverse surface of the film with acetate, the film becomes more labile and makes a better contact with the material. The peel can be washed in acid to remove any remaining matrix before mounting onto a slide with resin for further study.^[7] The method is somewhat destructive, as the acid etching used to remove the rock matrix can also destroy some finer detail; the fizzing caused by the reaction of the acid with the matrix breaks up less-robust cellular material.^[7] A second peel without further etching, a "rip peel", will remove any cell walls that are parallel to the surface, and would otherwise be destroyed when subjected to acid.^[7]

Details of the modern application of the method can be found in reference (^[8]). Even the latest technique does have some disadvantages; most notably, smaller fossils that may lie between cell walls will be washed away with the acid etch, and can only be recovered by a thin section preparation.^[9]

In order to mount the slides for microscopy, a series of steps are necessary:^[7]

A glass slide is wetted with acetone, and a fresh layer of acetate is placed upon it. The acetone allows the acetate to 'suck' itself onto the slide, maintaining a good contact by suction. This will later be dissolved, allowing sections of the resin-mounted peel to be cut for transmission electron microscopy.
A thin layer of epoxy resin is applied, covering the acetate and spreading onto the slide. This will serve to attach the preparation to the slide once the underlying acetate has been dissolved.
A glass plate is greased, and the smooth side of a peel pressed down onto it.
The rough side of this peel is covered with warmed (55 °C) epoxy resin, and pressed down onto the previously-prepared slide. After about 45 minutes the glass plate is removed, and the resin is left, warm, to cure.
The preparation is washed in acetone and acid to remove any residues, which would otherwise produce optical artefacts when imaged.

Specimens recovered by film pull are prone to wrinkling, especially if the surface to be peeled is not perfectly smoothed—if acetone pools, it can cause the acetate to wrinkle.^[8]

Transfer technique

The transfer technique is a technique to stabilise and prepare fossils by partially embedding them in plastic resins (i.e. epoxy or polyester) in order to preserve the position of the preserved fossil once all of the rock matrix is subsequently removed. Notable examples of this technique are fossils preserved in oil shale (such as those from the Messel Pit) or other substrates that will deteriorate under atmospheric conditions, or fossils preserved in acid-soluble carbonates (such as fossils from the Santana Formation).^[10] The technique is notable for delivering exquisite preparations of both very high scientific and display value, as the area exposed in this method is protected by the matrix prior to the preparation, while the initially exposed fossils are often subject to damage from improper mechanical removal of sediment or where the plane of splitting has extended through the fossil. This allows the potential to preserve microscopic details on the surface of the fossil.^[11]

The method was pioneered by Harry Toombs and A. E. Rixon of the British Museum in 1950^[12] with the introduction of the technique as a means of extracting fish fossils from acid-soluble carbonates. The technique permitted the preparation of delicate, fragmented, or otherwise unstable fossils by the removal of virtually all of the surrounding rock matrix. The resulting preparation retains the position of all of the parts of the fossil in the position in which they were preserved in the fossil. While the method developed by Toombs and Rixon calls for plastic resins, other substances, such as a mix of ground chalk and beeswax have been used.^[13]

While the original method was developed to deal with fossils freed from the matrix by acid, its most well known application is to the fossils from The Messel pit. These fossils, noted for their exquisite preservation, including soft tissue, body outline and even colour sheen on beetle wings, are notoriously difficult to preserve. The fossils themselves are flat, sometimes film-like on the surface of the rock layers. The oil shale contains 40% water. When a slab is broken free of surrounding rock, it will soon dry out and crack.^[14] A slab with a perfect fossil will turn to a heap of rubble in a few hours, destroying the fossil with it. This was the fate of numerous Messel fossils until the transfer technique was started to be applied in the 1970s.

In order to preserve the fossils once their slab is taken out of the rock, the fossil need to be transferred from the rock surface on to a durable, artificial surface. The water in the fossil itself also needs to be replaced.

As soon as the slab bearing the fossil is worked free from the rock, it is submerged in water to stop it from cracking. This involves packing it in plastic and sometimes wet newspaper. While in the wet state, it is cleaned up and all preparation needed for the transfer conducted.^[15]

Once ready for transfer, the fossil (but not the surrounding rock) is dried off with a blow-dryer. As soon as the fossil starts to lighten (a sign of drying), water-soluble lacquer is applied. The lacquer will penetrate the bone and other organic remains, but not the shale itself, as shale is impenetrable to watery solutions.

When the lacquer has set, a frame of modelling clay is built on the rock face around the fossil. A two-component epoxy is poured onto the frame, forming the new artificial surface for the fossil. The composition of the resin is important, as it will have to soak into the fossil to further strengthen it and to bind it to the new surface. This can be controlled by varying the resin viscosity.^[11]

When the epoxy has set, the slab is turned over, and preparation begins from the shale at the back. Layer by layer of oil-shale is removed with brush and scalpel. When the preparator hits the fossil, more lacquer and glue is applied to further stabilize the fragile fossil. When the work is done, all traces of oil-shale have been removed, only the fossil itself remains on the epoxy slab.^[16]

The contrasting physical property of the rock and fossil are essential for this technique to succeed. The organic remains of the fossil are porous and hygroscopic, while the oil-containing rock is not. Thus, the lacquer can penetrate fossils, and not rock, enabling the preparator to “glue” the fossil to the artificial slab, without at the same time gluing it to the shale.

Related Research Articles

Histology, also known as microscopic anatomy or microanatomy, is the branch of biology that studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures visible without a microscope. Although one may divide microscopic anatomy into organology, the study of organs, histology, the study of tissues, and cytology, the study of cells, modern usage places all of these topics under the field of histology. In medicine, histopathology is the branch of histology that includes the microscopic identification and study of diseased tissue. In the field of paleontology, the term paleohistology refers to the histology of fossil organisms.

Shellac is a resin secreted by the female lac bug on trees in the forests of India and Thailand. Chemically, it is mainly composed of aleuritic acid, jalaric acid, shellolic acid, and other natural waxes. It is processed and sold as dry flakes and dissolved in alcohol to make liquid shellac, which is used as a brush-on colorant, food glaze and wood finish. Shellac functions as a tough natural primer, sanding sealant, tannin-blocker, odour-blocker, stain, and high-gloss varnish. Shellac was once used in electrical applications as it possesses good insulation qualities and seals out moisture. Phonograph and 78 rpm gramophone records were made of shellac until they were gradually replaced by vinyl. By 1948 shellac was no longer used to make records.

<span class="mw-page-title-main">Nitrocellulose</span> Highly flammable compound

Nitrocellulose is a highly flammable compound formed by nitrating cellulose through exposure to a mixture of nitric acid and sulfuric acid. One of its first major uses was as guncotton, a replacement for gunpowder as propellant in firearms. It was also used to replace gunpowder as a low-order explosive in mining and other applications. In the form of collodion it was also a critical component in an early photographic emulsion, the use of which revolutionized photography in the 1860s. In the 20th century it was adapted to automobile lacquer and adhesives.

A resin is a solid or highly viscous liquid that can be converted into a polymer. Resins may be biological or synthetic in origin, but are typically harvested from plants. Resins are mixtures of organic compounds, and predominantly terpenes. Well known resins include amber, hashish, frankincense, myrrh and the animal-derived resin, shellac. Resins are commonly used in varnishes, adhesives, food additives, incenses and perfumes.

<span class="mw-page-title-main">Varnish</span> Transparent hard protective finish or film

Varnish is a clear transparent hard protective coating or film. It is not to be confused with wood stain. It usually has a yellowish shade due to the manufacturing process and materials used, but it may also be pigmented as desired. It is sold commercially in various shades.

Lacquer is a type of hard and usually shiny coating or finish applied to materials such as wood or metal. It is most often made from resin extracted from trees and waxes and has been in use since antiquity.

Collodion is a flammable, syrupy solution of nitrocellulose in ether and alcohol. There are two basic types: flexible and non-flexible. The flexible type is often used as a surgical dressing or to hold dressings in place. When painted on the skin, collodion dries to form a flexible nitrocellulose film. While it is initially colorless, it discolors over time. Non-flexible collodion is often used in theatrical make-up. Collodion was also the basis of most wet-plate photography until it was superseded by modern gelatin emulsions.

In biochemistry, cellulose acetate refers to any acetate ester of cellulose, usually cellulose diacetate. It was first prepared in 1865. A bioplastic, cellulose acetate is used as a film base in photography, as a component in some coatings, and as a frame material for eyeglasses; it is also used as a synthetic fiber in the manufacture of cigarette filters and playing cards. In photographic film, cellulose acetate film replaced nitrate film in the 1950s, being far less flammable and cheaper to produce.

<span class="mw-page-title-main">Acetone</span> Organic compound ((CH3)2CO); simplest ketone

Acetone is an organic compound with the formula (CH₃)₂CO. It is the simplest and smallest ketone. It is a colorless, highly volatile, and flammable liquid with a characteristic pungent odour, very reminiscent of the smell of pear drops.

<span class="mw-page-title-main">Methyl isobutyl ketone</span> Chemical compound

Methyl isobutyl ketone (MIBK, 4-methylpentan-2-one) is an organic compound with the condensed chemical formula (CH₃)₂CHCH₂C(O)CH₃. This ketone is a colourless liquid that is used as a solvent for gums, resins, paints, varnishes, lacquers, and nitrocellulose.

Also known as a "bonderizer" bonding agents are resin materials used to make a dental composite filling material adhere to both dentin and enamel.

Powder coating is a type of coating that is applied as a free-flowing, dry powder. Unlike conventional liquid paint, which is delivered via an evaporating solvent, powder coating is typically applied electrostatically and then cured under heat or with ultraviolet light. The powder may be a thermoplastic or a thermosetting polymer. It is usually used to create a thick, tough finish that is more durable than conventional paint. Powder coating is mainly used for coating of metal objects, particularly those subject to rough use. Advancements in powder coating technology like UV-curable powder coatings allow for other materials such as plastics, composites, carbon fiber, and medium-density fibreboard (MDF) to be powder coated, as little heat or oven dwell time is required to process them.

An enteric coating is a polymer barrier applied to oral medication that prevents its dissolution or disintegration in the gastric environment. This helps by either protecting drugs from the acidity of the stomach, the stomach from the detrimental effects of the drug, or to release the drug after the stomach. Some drugs are unstable at the pH of gastric acid and need to be protected from degradation. Enteric coating is also an effective method to obtain drug targeting. Other drugs such as some anthelmintics may need to reach a high concentration in a specific part of the intestine. Enteric coating may also be used during studies as a research tool to determine drug absorption. Enteric-coated medications pertain to the "delayed action" dosage form category. Tablets, mini-tablets, pellets and granules are the most common enteric-coated dosage forms.

<span class="mw-page-title-main">Compression fossil</span>

A compression fossil is a fossil preserved in sedimentary rock that has undergone physical compression. While it is uncommon to find animals preserved as good compression fossils, it is very common to find plants preserved this way. The reason for this is that physical compression of the rock often leads to distortion of the fossil.

<span class="mw-page-title-main">Cellulose acetate phthalate</span> Chemical compound

Cellulose acetate phthalate (CAP), also known as cellacefate (INN) and cellulosi acetas phthalas, is a commonly used polymer phthalate in the formulation of pharmaceuticals, such as the enteric coating of tablets or capsules and for controlled release formulations. It is a cellulose polymer where about half of the hydroxyls are esterified with acetyls, a quarter are esterified with one or two carboxyls of a phthalic acid, and the remainder are unchanged. It is a hygroscopic white to off-white free-flowing powder, granules, or flakes. It is tasteless and odorless, though may have a weak odor of acetic acid. Its main use in pharmaceutics is with enteric formulations. It can be used together with other coating agents, e.g. ethyl cellulose. Cellulose acetate phthalate is commonly plasticized with diethyl phthalate, a hydrophobic compound, or triethyl citrate, a hydrophilic compound; other compatible plasticizers are various phthalates, triacetin, dibutyl tartrate, glycerol, propylene glycol, tripropionin, triacetin citrate, acetylated monoglycerides, etc.

Extraction in chemistry is a separation process consisting of the separation of a substance from a matrix. The distribution of a solute between two phases is an equilibrium condition described by partition theory. This is based on exactly how the analyte moves from the initial solvent into the extracting solvent. The term washing may also be used to refer to an extraction in which impurities are extracted from the solvent containing the desired compound.

Small carbonaceous fossils (SCFs) are sub-millimetric organic remains of organisms preserved in sedimentary strata.

<span class="mw-page-title-main">Coal ball</span> Stone of peat that did not turn into coal

A coal ball is a type of concretion, varying in shape from an imperfect sphere to a flat-lying, irregular slab. Coal balls were formed in Carboniferous Period swamps and mires, when peat was prevented from being turned into coal by the high amount of calcite surrounding the peat; the calcite caused it to be turned into stone instead. As such, despite not actually being made of coal, the coal ball owes its name to its similar origins as well as its similar shape with actual coal.

Conservation and restoration of ceramic objects is a process dedicated to the preservation and protection of objects of historical and personal value made from ceramic. Typically, this activity of conservation-restoration is undertaken by a conservator-restorer, especially when dealing with an object of cultural heritage. Ceramics are created from a production of coatings of inorganic, nonmetallic materials using heating and cooling to create a glaze. These coatings are often permanent and sustainable for utilitarian and decorative purposes. The cleaning, handling, storage, and in general treatment of ceramics is consistent with that of glass because they are made of similar oxygen-rich components, such as silicates. In conservation ceramics are broken down into three groups: unfired clay, earthenware or terracotta, and stoneware and porcelain.

Paraloid B-72 or B-72 is a thermoplastic resin that was created by Rohm and Haas for use as a surface coating and as a vehicle for flexographic ink. Subsequently, it has found popular use as an adhesive by conservator-restorers, specifically in the conservation and restoration of ceramic objects, glass objects, the preparation of fossils, the hardening of piano hammers, and can also be used for labeling museum objects.

References

↑ Wylie, Caitlin Donahue (2009). "Preparation in action: Paleontological skill and the role of the fossil preparator". Fossil Preparation: Proceedings of the First Annual Fossil Preparation and Collections Symposium.
↑ Edwards, D. (1982), "Fragmentary non-vascular plant microfossils from the late Silurian of Wales", Botanical Journal of the Linnean Society, 84 (3): 223–256, doi:10.1111/j.1095-8339.1982.tb00536.x
↑ Hernick, L.; Landing, E.; Bartowski, K. (2008). "Earth's oldest liverworts—Metzgeriothallus sharonae sp. Nov. From the Middle Devonian (Givetian) of eastern New York, USA". Review of Palaeobotany and Palynology. 148 (2–4): 154–162. Bibcode:2008RPaPa.148..154H. doi:10.1016/j.revpalbo.2007.09.002.
↑ Walton, J. (1928). "A Method of Preparing Sections of Fossil Plants contained in Coal Balls or in other Types of Petrifaction". Nature. 122 (3076): 571. Bibcode:1928Natur.122..571W. doi: 10.1038/122571a0 . S2CID 4102720.
↑ Walton, J. (1930). "Improvements in the Peel-Method of Preparing Sections of Fossil Plants". Nature. 125 (3150): 413–414. Bibcode:1930Natur.125..413W. doi:10.1038/125413b0. S2CID 4083168.
↑ Joy, K. W.; Willis, A. J.; Lacey, W. S. (1956). "A Rapid Cellulose Peel Technique in Palaeobotany". Annals of Botany. 20 (4): 635–637. doi:10.1093/oxfordjournals.aob.a083546.
1 2 3 4 Holmes, J.; Lopez, J. (1986). "The disappearing peel technique: an improved method for studying permineralized plant tissues". Palaeontology. 29 (4). 787–808.
1 2 Galtier, J.; Phillips, T. L. (1999). "The acetate peel technique". In Jones, T. P.; Rowe, N. P. (eds.). Fossil Plants and Spores: Modern Techniques. The Geological Society, London. pp. 67–70. ISBN 978-1-86239-035-5.
↑ Taylor, T. N.; Krings, M.; Dotzler, N.; Galtier, J. (2011). "The Advantage of Thin Section Preparations over Acetate Peels in the Study of Late Paleozoic Fungi and Other Microorganisms". PALAIOS. 26 (4): 239–244. Bibcode:2011Palai..26..239T. doi:10.2110/palo.2010.p10-131r. S2CID 128546972.
↑ Maisey, J. G., Rutzky, I., Blum, S. & W. Elvers (1991): Laboratory Preparation Techniques. In Maisey, j:G. (ed): Santana Fossils: An Illustrated Atlas, Tfh Pubns Inc. ISBN 0866225498. pp 99–103.
1 2 Barling, Nathan; David M. Martill; Florence Gallien (2019). "The resin transfer technique: an application to insect fossils in laminated limestones of the Crato Formation (Lower Cretaceous) of north-east Brazil" (PDF). Cretaceous Research. 98: 1–2. Bibcode:2019CrRes..98..179B. doi:10.1016/j.cretres.2019.02.009. S2CID 134208049.
↑ Toombs, Harry; A. E. Rixon (1950). "The use of plastics in the "transfer method" of preparing fossils". The Museums Journal. 50: 105–107. Archived from the original on 2016-03-04. Retrieved 2020-08-21.
↑ Keller, T.; Frey, E.; Hell, R.; Rietschel, S.; Schaal, S.; Schmitz, M. (1991). "Ein Regelwerk für paläontologische Grabungen in der Grube Messel". Paläontologische Zeitschrift. 65 (1–2): 221–224. Bibcode:1991PalZ...65..221K. doi:10.1007/BF02985786. S2CID 128399238.
↑ Messel Oil Shale Fossil Site Lagerstatte, Virtual fossil museum website
↑ Messel Research Station, Senckenberg Forschungsinstitut und Naturmuseum website
↑ Messel Fossils from Germany website Archived 2016-03-04 at the Wayback Machine

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[Wylie-1] Wylie, Caitlin Donahue (2009). "Preparation in action: Paleontological skill and the role of the fossil preparator". Fossil Preparation: Proceedings of the First Annual Fossil Preparation and Collections Symposium.

[Edwards1982-2] Edwards, D. (1982), "Fragmentary non-vascular plant microfossils from the late Silurian of Wales", Botanical Journal of the Linnean Society, 84 (3): 223–256, doi:10.1111/j.1095-8339.1982.tb00536.x

[Hernick2008-3] Hernick, L.; Landing, E.; Bartowski, K. (2008). "Earth's oldest liverworts—Metzgeriothallus sharonae sp. Nov. From the Middle Devonian (Givetian) of eastern New York, USA". Review of Palaeobotany and Palynology. 148 (2–4): 154–162. Bibcode:2008RPaPa.148..154H. doi:10.1016/j.revpalbo.2007.09.002.

[Walton1928-4] Walton, J. (1928). "A Method of Preparing Sections of Fossil Plants contained in Coal Balls or in other Types of Petrifaction". Nature. 122 (3076): 571. Bibcode:1928Natur.122..571W. doi: 10.1038/122571a0 . S2CID 4102720.

[Walton1930-5] Walton, J. (1930). "Improvements in the Peel-Method of Preparing Sections of Fossil Plants". Nature. 125 (3150): 413–414. Bibcode:1930Natur.125..413W. doi:10.1038/125413b0. S2CID 4083168.

[6] Joy, K. W.; Willis, A. J.; Lacey, W. S. (1956). "A Rapid Cellulose Peel Technique in Palaeobotany". Annals of Botany. 20 (4): 635–637. doi:10.1093/oxfordjournals.aob.a083546.

[Holmes1986-7] 1 2 3 4 Holmes, J.; Lopez, J. (1986). "The disappearing peel technique: an improved method for studying permineralized plant tissues". Palaeontology. 29 (4). 787–808.

[bare_url-8] 1 2 Galtier, J.; Phillips, T. L. (1999). "The acetate peel technique". In Jones, T. P.; Rowe, N. P. (eds.). Fossil Plants and Spores: Modern Techniques. The Geological Society, London. pp. 67–70. ISBN 978-1-86239-035-5.

[9] Taylor, T. N.; Krings, M.; Dotzler, N.; Galtier, J. (2011). "The Advantage of Thin Section Preparations over Acetate Peels in the Study of Late Paleozoic Fungi and Other Microorganisms". PALAIOS. 26 (4): 239–244. Bibcode:2011Palai..26..239T. doi:10.2110/palo.2010.p10-131r. S2CID 128546972.

[10] Maisey, J. G., Rutzky, I., Blum, S. & W. Elvers (1991): Laboratory Preparation Techniques. In Maisey, j:G. (ed): Santana Fossils: An Illustrated Atlas, Tfh Pubns Inc. ISBN 0866225498. pp 99–103.

[Barling-11] 1 2 Barling, Nathan; David M. Martill; Florence Gallien (2019). "The resin transfer technique: an application to insect fossils in laminated limestones of the Crato Formation (Lower Cretaceous) of north-east Brazil" (PDF). Cretaceous Research. 98: 1–2. Bibcode:2019CrRes..98..179B. doi:10.1016/j.cretres.2019.02.009. S2CID 134208049.

[12] Toombs, Harry; A. E. Rixon (1950). "The use of plastics in the "transfer method" of preparing fossils". The Museums Journal. 50: 105–107. Archived from the original on 2016-03-04. Retrieved 2020-08-21.

[13] Keller, T.; Frey, E.; Hell, R.; Rietschel, S.; Schaal, S.; Schmitz, M. (1991). "Ein Regelwerk für paläontologische Grabungen in der Grube Messel". Paläontologische Zeitschrift. 65 (1–2): 221–224. Bibcode:1991PalZ...65..221K. doi:10.1007/BF02985786. S2CID 128399238.

[14] Messel Oil Shale Fossil Site Lagerstatte, Virtual fossil museum website

[15] Messel Research Station, Senckenberg Forschungsinstitut und Naturmuseum website

[16] Messel Fossils from Germany website Archived 2016-03-04 at the Wayback Machine

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