La Brea Tarpit

STORY BY James Sullivan

Published: August 13, 2013

The Rancho La Brea Tar Pit of Los Angeles has been infamous as testimony of a bygone Ice Age, days before the dawning of humanity, a time when strange titans dominated the North American wilderness – mammoths, dire wolves and saber tooth cats, creatures of a savage time that met a dismal and merciless fate. The result is a graveyard of these fantastic animals – but the preservation of the tarpit may prove itself useful in another way, in a study conducted by researchers from the University of Kansas suggests, led by Drs. John Holden, Anna Harris, and R. Timm and published in the scientific journal Plosoneearlier this month, being key indicators at establishing the times of death of various Ice Age mummies.

What is particularly unusual in this study, is that rather than the mammoths or giant sloths being of interest, rather it was the smaller, more familiar fossils of creatures that still live today, that were the focus of the study – fossilized beetles and termites. Two percent of all bones recovered from the tar pits show indication of damage produced by insects, particularly termites and a genus of beetles that were collected from outside Dr. Timm's home – dermestid beetles, known for their practice of peeling away the decomposing flesh from bones of carcasses, as well as the Eleodes larvae, one of the most infamous maggots of Southern California. They are typically used in forensics, helping to determine the time of death, although in such a case as the La Brea project, the time of death may span as far back as 18,000 years ago.

In the study, these creatures were given chicken bones and pork ribs and the damage done to areas of bone were compared to the bones of Pleistocene era predators, all of which suffered damage from similar insects, magnified up to 40 times by microscope. These acted as a comparative group, exposed to temperatures that fluctuated between 25-30 degrees celsius, the ideal temperature at which larvae eggs hatch. Over a 4-5 month period, the insects did comparable damage to the chicken and pork bones, suggesting that such damage could occur over a span of time that is compatible with the warm season of the Pleistocene Age, a time at which Los Angeles would have been 18% cooler than it is today.

The parasites, in death, seem to have quite a significant role to play in determining the nature of an extinct ecosystem. The damage to the bone is not only the result of their feeding, but also of their entire life processes, as they tunneled through hollow networks of bone in order to establish their nests and fertilize their eggs, even leaving indications of when the larvae entered their pupation stage. By understanding how long the life cycle lasted, scientists can infer how long it took for the creatures to submerge beneath the tar with their flesh still being intact, as well as what seasons in which they died, when the tar would actually have enough osmotic pressure to allow the entry of insects, and during what seasons impact on the tar beds would cause them to give way.

Other Stories by James Sullivan
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