bogs, oil seeps, paraffin, tar pits and asphalt are good
sources for fossils that have been chemically preserved
(Garcia & Miller, 1998, p. 15). Paraffin
mines and peat bogs can preserve soft tissue. Tar pits or asphalt
preserve only hard parts such as bones, shells or exoskeletons.
In 1907, a paraffin mine in Poland produced the head, forelegs,
and skin of a woolly rhinoceros (Rich,
p. 3). The
Rancho La Brea Tar Pits in California, Big Bone Lick in
and Talara, Peru are well known sites for fossils preserved
pits (Garcia & Miller, 1998, p. 15).
La Brea within the city of Los Angeles is one of the richest
deposits of ice aged animals. The sabre-toothed cat Smilodon
fatalis, the imperial mammoth Mammuthus imperator,
the American mastodon Mammut americanum, and the
sloth Glossotherium harlani are just some of the
ice aged mammals that capture the public's imagination.
of plant and animal species have been found trapped within
these asphalt deposits providing a window into a North
American Pleistocene ecosystem.
of the fossils excavated at Rancho La Brea are carbon
at between 11,000 and 38,000 years old. The asphalt rich
sediments that contain this concentration lagerstatte
were deposited during the last ice age (Wisconsinan Glaciation),
which places them in the Upper Pleistocene Epoch. Shallow
asphalt pools formed animal traps during the summer.
During the winter these pools may have solidified. As seasons
changed, heat from the summer sun would once again set
the traps for foraging herbivores.
is a preservation bias for carnivores, young and maimed
individuals. Young and maimed animals were more
susceptible to becoming trapped in the asphalt pools. Scavengers
to the carcasses accumulating in the pools.
soft tissue is not preserved the bones retain much
of their original composition. Rapid burial followed by
accounts for the excellent bone preservation (Nudds
& Selden, 2008, p 262-268). The bones are black with
tar and have
the smell of petroleum. Scientists
organisms with their living relatives (Prothero,
2004, p. 9).
Rancho La Brea literally translates to "the tar ranch".
The naturally occurring petroleum based substance is more
properly referred to as asphalt (Nudds & Selden, 2008,
F.A. & Miller, D.S. (1998). Discovering Fossils:
How to Find and Identify Remains of the Prehistoric Past.
Pennsylvania: Stackpole Books.
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.
P.V., Rich T. H., Fenton, M.A., & Fenton, C.L. (1996). The
Fossil Book: A Record of Prehistoric Life. Mineola,
NY: Dover Publications, Inc.