BIOGENIC
PRODUCTS
Biogenic products constitute another category of
fossils. Many paleontologists refer to such things as trace fossils, but
they really aren't. Biogenic products are objects produced by
ancient organisms. This is different from what trace fossils are
(footprints, tracks, burrows, trails, bitemarks, etc.).
Examples of fossil biogenic products include eggs,
amber (fossilized tree sap), coprolites (fossilized feces), and spider silk.
FOSSIL EGGS
Fossil eggs are good examples of biogenic products -
objects produced by ancient organisms. The most famous fossil eggs are
those of dinosaurs. Dinosaur nests having eggs in their original laying
position are known from several localities around the world. Sometimes,
x-ray analysis or cat-scan analysis shows the presence of dinosaur embryos
inside intact eggs. The embryos would be body fossils, but the
surrounding eggshell material is a biogenic product.
Dinosaur eggshell fragment (5.2 cm across; eggshell thickness is 4 to 5 mm) -
note the surface ornament consisting of large pustules or tubercles; commercial
specimen identified as a sauropod dinosaur eggshell from the Upper Cretaceous
of Patagonia, Argentina.
AMBER & COPAL
Fossilized tree sap (resin) is called amber.
Resin that has not been completely altered to amber is called copal
(“subfossilized tree sap”). The general term for such materials is resinite.
Copal ranges in age from several years old to ~33,000
years old. True amber ranges in age from a few million to hundreds of
millions of years old - as far back as the Carboniferous.
Amber and copal vary in color, but are typically a
rich, light- to dark-golden brown. Resinites are quite lightweight (but
amber is denser than copal), and show conchoidal fracture when broken.
Copal often is, and has been, passed off as true amber.
Amber is valued as a gem material for its transparency
and distinctive color. Amber and copal are also valued for the frequent
presence of fossil inclusions, typically insects.
Amber (resinite) - raw amber from the Baltics (left: 2.7 cm
across; right: 3.1 cm across).
Baltic amber (resinite or succinite) (polished; 16 mm across) showing transparency and
included fossil fly (Arthropoda, Insecta, Diptera, Brachycera). The fly has a milky-white decay coating.
Stratigraphy & age: “Blue Earth layer”, “Amber Formation”, Lutetian
Stage, lower Middle Eocene.
Locality:
Kaliningrad District, Baltic Sea, far-western Russia.
Copal
(left: 4.6 cm across; right: 4.9 cm across) - raw copal (likely
very young) showing obvious crazing (surficial & near-surface
cracking, the result of evaporation of volatile organics; amber does not craze
quickly or as deeply as copal does - see Grimaldi, 1996).
Some modern trees release relatively copious amounts
of resin. The photos below show Acacia trees in the South Australian
Outback that have oozed masses of resin.
Resin mass on Acacia tree (above & below)
near Old Wirrealpa Mine, north of the Blinman-Wirrealpa Road, Flinders Ranges,
South Australian Outback.
Resin mass on Acacia tree (above & below)
near Old Wirrealpa Mine, north of the Blinman-Wirrealpa Road, Flinders Ranges,
South Australian Outback.
Some references on amber & fossils in amber:
Poinar, G. & R. Poinar. 1994. The
Quest for Life in Amber. Reading, Massachusetts. Addison-Wesley
Publishing Company. 219 pp.
Dahlström, A., L. Brost & J. Leijonhufvud.
1996. The Amber Book. Tuscon, Arizona. Geoscience
Press, Inc. 134 pp.
Grimaldi, D.A. 1996. Amber, Window to
the Past. New York. American Museum of Natural History.
215 pp.
Ross, A. 1998. Amber.
London. The Natural History Museum. 73 pp.
Poinar, G.O. & R. Milki. 2001. Lebanese
Amber, the Oldest Insect Ecosystem in Fossilized Resin. Corvallis,
Oregon. Oregon State University Press. 96 pp.
Geirnaert, E. 2002. L'Ambre, Miel de
Fortune et Mémoire de Vie. Monistrol-sur-Loire, France. 176 pp.
[in French]
Hong Youchong. 2002. Amber Insects of
China. Beijing. Beijing Scientific Publishing House. 653
pp. 48 pls. [in Chinese]
Weitschat, W. & W. Wichard. 2002. Atlas
of Plants and Animals in Baltic Amber. Munich. Dr. Friedrich
Pfeil. 256 pp. [excellent resource! highly recommended!]
Selden, P. & J. Nudds. 2004. Baltic
amber. pp. 131-141 in Evolution of Fossil Ecosystems.
Chicago. University of Chicago Press.
COPROLITES
Coprolites are fossilized fecal masses. They
range in size from microscopic-sized pellets to moderately sizable dung piles (see
dinosaur coprolite below). The most famous examples are “Washington
coprolites” from the Miocene Wilkes Formation of Washington State, USA.
These are now considered cololites (intestinal casts). True coprolites
are fossilized dung. Coprolite thin sections often reveal fragments of
incompletely digested plant matter or sometimes undigested animal tissue.
So, coprolite studies can provide information about
the diet of ancient organisms, assuming the coprolite maker is known with some
specificity (which is very frequently not the case).
Coprolite - dinosaur coprolite, attributed to the Morrison Formation (Jurassic)
of Cortez, Colorado, USA.