By William Weston



New evidence acquired from an ongoing excavation project at Rancho La Brea has led to a major re-evaluation of how the fossils were deposited. The traditional idea that animals were trapped in continuously active, open pools of tar has been discarded, and new theories of entrapment and deposition emerged. Although more realistic in some ways than the old theory, the alternatives suffer from the same inability to provide a defendable, gradualistic explanation. This critique represents a preparatory stage in the development of a theory that discards the principle of animal entrapments and advances the concept of a diluvial process in the formation of the tar pit fossil beds.



Dr. John C. Merriam, a vertebrate paleontologist at the University of Berkeley, first heard of the fossils of Rancho La Brea in 1905 from Union Oil geologist William W. Orcutt. After viewing the fossils and visiting the source beds, Merriam wrote an article in 1906 about a pool of tar that deceived, trapped, and swallowed up its victims. Two years later, he wrote an expanded treatment of the subject for a popular magazine. The editor’s introduction to the article had the following words:


This sticky pool of water and tar has been a Death Trap of the Ages. Here, for centuries, evidently, the enormous ground-sloth and other clumsily moving creatures of his kind came for water, only to be held relentlessly; herds of bison and horses were entombed, extinct forms with whose bones mingle those of the mammoth and the camel. To this helpless prey, snared for them in this bird-lime bed, came the lords of the era, the huge sabre-tooth tiger and monster wolf, the largest of the dog family. Trapped in their turn, they, too, fed the black maw of the asphalt pool and the death trap baited itself anew (Merriam, 1908)….

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