Abstract

The famous Rancho La Brea tar seeps of Southern California trapped thousands of Pleistocene and early Holocene vertebrates, preserving them as jumbled columns of millions of disarticulated bones. Previous work has contributed to a hypothetical entrapment scenario, however, it lacks detail in the period between the time the animals perished and the permeation of their bones with tar. Additionally, previous work has shown that skeletal elements moved apart from each other at least 1–3 meters but it is unclear whether this movement occurred near the surface of the tar, soon after submersion, or later after burial by sediment and compaction. To help answer these questions of disarticulation and transport, we conducted an actualistic experiment to record the progress of microbial succession and skeletonization of specimens in tar. We submerged dismembered bobcat (Lynx rufus) carcasses in an undisturbed tar seep and recorded the progress of microbial faunal changes and tissue decay. Microbial communities differed between tar environments and tissue decay, and changes in microbial communities across the stages of decay indicate rapid microbial succession, with the microbes most involved in the decay likely originating from the liquid surface tar. The minimum time to achieve clean bone was 40 days, from which we conclude that a surficial process may have been responsible for the movement of bones in the La Brea tar seeps.

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