can replace bone, shell, wood, and even soft body parts
as they dissolve away due to the action of water and decay.
Replacement and mineralization are terms used to describe
this fossilization process (Garcia & Miller, 1998,
p. 15). Part of the ammonite shell above has been replaced
The replacement of soft or hard body parts may occur when minerals precipitate
out of solution due to the action of bacteria or pH changes.
replacement coats of bacteria quickly mineralize the decaying
tissue. If replacement results in a fossil that is completely
articulated with three-dimensional fidelity the
process is referred to as mineral
(Grimaldi and Engel, 2005, p.
Grimaldi and Engel also
classify permineralization as a type of mineral replication that
is a result of microbial decay. Organic
residue on compression fossils can be replaced by minerals
leaving an impression coated with a mineral. Pyrite is
a common replacement mineral. In pyritization sulfur reducing
bacteria facilitate the precipitation of pyrite during
Lagerstätten known as Beecher's
Bed in New York is famous for its pyritized trilobites.
Both the exoskeleton and soft body parts, including, antennae,
legs, muscles, and digestive tract, have been preserved
the mineral pyrite (Etter, 2002, p. 131).
the Orsten deposits of Sweden the meiofauna making up the
of a flocculent-layer just above the seabed is exquisitely
preserved by phosphatization. Eyes, hairs, spines, muscle
scars, joints, pores, and soft body parts have been preserved
on miniature late Cambrian arthropods. Exoskeletal replacement
and or coating by calcium phosphate occur only on specimens
less than 2 mm is size. The
Orsten Lagerstätten is important because it helps to
deepen our understanding of arthropods as many larval stages
2002, pp. 117-121).
examples of leaves, stems, cones, and seeds of Carboniferous
plants along with animal life can be found in the Lagerstätten
known as Mazon Creek, which is just 150 km southwest of
Chicago, Illinois. The soft and hard parts of plants and animals
are replaced with the mineral siderite (iron carbonate). Subtle
pH changes created
by the decaying body of the buried organism caused
available iron carbonate to precipitate. Thus, the organism
nucleation site for the formation of a siderite nodule. When
these nodules are split open, the fossil appears as a 3-D external
cast and mold. Mold surfaces may be coated with kaolinite, pyrite,
calcite or sphalerite. Plant material is sometimes covered
with a carbonaceous film (Nudds & Selden, 2004, p.
material from an Oligocene deposit preserved in barite-
be found near
town of Steinhardt Germany. When split open some of these
nodules reveal molds and casts of plant material replaced
barite (barium sulfate).
process that forms a concretion or nodule, which may contain
replacement fossil, is called authigenic cementation
or authigenic mineralization (Prothero, 2004,
p. 437; Cleal & Thomas, 2009, p. 7). Authigenic minerals
grow in place rather than being transported or deposited.
or nodules are found in the place they formed or in
for "in the place").
C.J. & Thomas, B.A. (2009). Introduction to Plant
Kingdom: Cambridge University Press.
W.. (2002). Beecher's Trilobite Bed: Ordovician Pyritization
for the Other Half of the Trilobite. In Bottjer, D.J., Etter,
W., Hadadorn, J.W., & Tang, C.M. [Eds.] Exceptional
Fossil Preservation: A Unique View on the Evolution of Marine
Life (131-141). New York: Columbia University Press.
F.A. & Miller, D.S. (1998). Discovering Fossils:
How to Find and Identify Remains of the Prehistoric Past.
Pennsylvania: Stackpole Books.
Grimaldi, D. & Engel, M.S., (2005). Evolution
of the Insects. New York: Cambridge University Press.
J.R. & Selden P.A. (2008). Fossil Ecosystems
of North America: A Guide to the Sites and Their Extraordinary
Biotas. Chicago: University of Chicago Press.
D.R. (2004). Bringing Fossils to Life: An Introduction
to Paleobiology [2nd edition]. New York: McGraw-Hill.
C.M. (2002). Orsten Deposits from Sweden: Miniature
Late Cambrian Arthropods. In Bottjer, D.J.,
Etter, W., Hadadorn, J.W., & Tang, C.M. [Eds.] Exceptional
Fossil Preservation: A Unique View on the Evolution
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