During the cooler, winter months the shallow asphalt pools presented no threat to the local animal communities for the simple reason that the asphalt hardens with the cool temperatures, while the winter and spring rain filled the streams in which the asphalt accumulated with sand and silt inhibiting entrapment.

    However during the hot summer months the streams dried up and warmed the semi-solid asphalt into a gooey liquid. The surface of the shallow asphalt pools were often hidden by a surface layer of fallen leaves and dust. Animals would unknowingly walk, or get chased into the asphalt pools and become trapped. Inevitably a large number of predators and scavengers would follow the trapped animal into the asphalt and get trapped themselves. This would then attract more scavengers leading to a high number of predators and scavengers trapped in the asphalt, compared with the first animal trapped, which is most likely to have been a herbivore.

    In normal ecological systems herbivores outnumber predators many times, however the tar pits typically contain seven predators to every one herbivore. While the preservation of these animals is exceptional it must be remembered that they are not representative of the original community, although a lot can be inferred about the original community by looking at modern communities based on the animals found in the tar pits. Once the animals are trapped, they die and then preservation processes start.

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