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Baltic
Amber with Inclusion Order Hymenoptera Specimen 8mm Cenozoic; Paleocene; Eocene Yantarny, Kaliningrad, Russia 4.5 cm long x 3 cm wide x 1.5 cm thick Click on specimen to open up a close-up window. |
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Amber is referred to as petrified tree resin or sap. I prefer petrified tree resin as the term sap refers to fluids transported by xylem or phloem tissues (Raven, Evert, & Curtis, 1981, p. 659). Conifers and some deciduous trees produce resin in response to injury. Resins are viscous liquids that contain volatile terpene compounds and organic solids. Under the right conditions resins polymerize and harden with age, turning into copal. After several million years copal matures into amber. Tree resin breaks down when exposed to drying and oxidation within just a few thousand years. It is not surprising then that amber deposits do not represent forest floor environments. Amber deposits usually represent marine environments. Amber deposits form when resins produced in forests are transported by water to oceans or lakes, where they are deposited into the sedimentary layers. Quick transport and deposition protects the resin from weathering. Once deposited, the resin chemically matures into intermediate forms called copals and finally into amber after millions of years. The amberization process is estimated to take between 2 and 10 million years. However, the type of depositional environment may also affect the time needed for amberization. Amber from Borneo is found in sand and clay sediments deposited in a deep ocean 12 million years ago. The material that comes out of the sandstone has matured into amber, while the specimens from the clay are still copal (Ross, 2010, pp 8-9). Petrified resins have been found in Carboniferous, Triassic, and Jurassic deposits, but represent minute amounts of resins produced inside trees. Resin that collects inside trees does not act as an insect trap. The first occurrence of fossil containing amber is Cretaceous in age. The majority of amber deposits that contain fossils were formed during the Cenozoic (Weitschat & Wichard, 2002, pp.9-10). Fossils entombed in amber are referred to as inclusions. Although the organisms often look complete, most appear to be thinly lined hollow spaces (Weitschat & Wichard, 2002, p. 29). However, under the right conditions the internal organs can be well preserved. The preserved internal organs of a bee exhumed from Dominican amber have been imaged using an electron microscope (Grimaldi & Engel, 2005, p. 59). Studies using scanning electron microscopes as well as transmission electron microscopes have revealed internal organ preservation in Baltic amber spiders and gnats. It seems that many orangisms are preserved through mummification. In the process of mummification, dehydration results in up to a 30% decrease in volume of tissues. The decrease in tissue volume gives the organisms the appearance of an empty husk (Selden & Nudds, 2004, p. 134). The shape of a specimen can be a clue to whether the amber formed inside the tree as an internal resin accumulation or outside the tree as an external resin accumulation. Resin can collect inside the void of a tree, drip off a branch, or flow along the outer bark. Resin that collects inside a tree usually does not contain fossils. Resin that accumulates on the outside of a tree can act as an insect trap. Fossils are almost exclusively found in specimens formed by successive resin flows that collected on the outside of the tree. These specimens are referred to as Schlaube (Weitschat & Wichard, 2002, p. 12). Organisms become trapped in the resin and are then covered by a successive resin flow. You can usually see the plane representing a successive resin flow; it often looks like a fracture in the amber. Amber can represent a brief snapshot in time. Amber has preserved insect developmental stages, mating, egg laying, brood care, feeding, as well as various symbiotic relationships. Amber with and without fossils can be quite valuable so, it is often faked. See Ross (2010) for an excellent discussion regarding materials used to make fake amber and tests that can be used to distinguish real amber from imitations (pp. 11-15).
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 Spider Cenozoic; Paleocene; Eocene Primorskoje, Kaliningrad, Russia |
 Spider Cenozoic; Paleocene; Eocene Primorskoje, Kaliningrad, Russia |
 Insect in Amber |
 Insect in Amber |
Bibliography |
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Grimaldi, D. & Engel, M.S., (2005). Evolution of the Insects. New York: Cambridge University Press. Raven, P.H., Evert, R.F., & Curtis, H. (1981). Biology of Plants [3rd Ed]. New York: Worth Publishers, Inc. Ross, A. (2010). Amber: The Natural Time Capsule. New York: Firefly Books. Selden
P. & Nudds, J. (2004). Evolution of Fossil Ecosystems.
Chicago: The University of Chicago Press. |
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