Rancho La Brea - Fossil Ecosystems of North America: A Guide to the Sites and their Extraordinary Biotas - page 250

mammoths, bison, and Man, entered
North America. Gradual changes in the
North American mammalian fauna
resulting from such migration are used to
define a succession of North American
Land Mammal Ages.
However, at the close of the Wisconsinan
glaciation, some time between 12,000 and
10,000 years ago, the mammal faunas across
the globe underwent severe changes. In
North America 73% of the large mammals
(33 genera) became extinct, including
mammoths, mastodons, horses, tapirs,
camels, and ground sloths, together with
their predators such as sabre-toothed cats.
Whether this was caused simply by climatic
changes at the end of the Ice Age, or
whether it was the effect of excessive
hunting by Man, is still the focus of much
debate.
Within the City of Los Angeles, at a
locality known as Rancho La Brea ( 284 ,
285 ), can be found one of the world's
richest deposits of Ice Age fossils.
Preserved in asphalt-rich sediments, so
numerous are the remains that they can
truly be considered as a Concentration

Lagerstätte. Their diversity provides a
virtually complete record of life in the
Los Angeles Basin between 10,000
and 40,000 years ago, during this
vital period at the close of the Ice Age
in North America. This exceptional
biota defines the Rancholabrean Land
Mammal Age (Savage, 1951), and
includes approximately 60 different
mammal species ranging in size from
huge mammoths to the Californian
pocket mouse. This virtually entirely
preserved ecosystem also includes
reptiles such as snakes and turtles,
amphibians such as frogs and toads,
birds, fish, mollusks, insects, spiders, and
numerous plants including microscopic
pollen and seeds.

H ISTORY OF DISCOVERY AND
EXPLOITATION OF R ANCHO
L A B REA
The naturally occurring asphalt in this area
( 286 ) has been used by man since
prehistoric times. The local Chumash and
Gabrielino Indians used the sticky 'tar' both
as a glue for making weapons, vessels, and

286

286 Naturally occurring
asphalt pool at Hancock
Park, Los Angeles.