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Ice Age Insects

Beetles from the La Brea Tar Pits update our understanding of Southern California's Ice Age climate

Photo by Joyce Gross, UC Berkeley

Ice Age Insects
Researchers dated beetle species from the La Brea Tar Pits that are still alive today, such as this darkling beetle. We know a great deal about them — their diet, habitat, distribution, and climate sensitivity.

What was the climate of Ice Age Los Angeles? Scientists have long thought it was most likely colder and rainier than it is today, but some beetles beg to differ.

Stuck in the muck of the La Brea Tar Pits, in between saber-toothed cats and mammoths, there are untold numbers of insects. These microfossils (a group that includes insects, plants, rodents, small birds, reptiles, fish, shells, and other small materials) can sometimes tell us more about the past than even the most impressive mastodon skull. Many of them are “climate indicators” — species that are so sensitive to climate conditions we can draw insights from their presence in the fossil record.

But first you need to know how old they are.

Until recently none of the specimens in the vast insect collections at the La Brea Tar Pits and Museum had been dated, so the chronology of these Ice Age insects was a complete mystery. But a new method for dating chitin — a component of insect exoskeletons — opened a new avenue to explore the climate history of the Los Angeles Basin.

a beetle fossil, an oblong-shaped brown exoskeleton with bumps running along it.
A darkling beetle fossil from the La Brea Tar Pits. CP image #0000 2222 9825 2094 provided by the Berkeley Fossil Insect PEN, photography by Rosemary Romero.

A team led by Anna Holden, a PhD Candidate at the Richard Gilder Graduate School at the American Museum of Natural History and Research Associate at the La Brea Tar Pits and Museum, used the first successful radiocarbon dating methods for insects to determine the age of 182 beetles representing seven species from the La Brea Tar Pits Museum collection — the biggest group of specimens ever radiocarbon dated at once at the La Brea Tar Pits.

What they found among these ground beetles and darkling beetles was a record reaching back a staggering 50,000 years. And the presence of these climate-sensitive beetles throughout this swath of time sheds new light on L.A.’s paleoclimate — past climate conditions. Contrary to the prevailing interpretation of a colder, wetter Ice Age L.A. Basin, these beetles suggest that prehistoric Los Angeles had the same mild, Mediterranean climate Angelenos enjoy today.

“Insects are the unsung heroes of climate,” said Holden. “We have this treasure trove of information. We’ve only scratched the surface, and already it’s added to regional understanding for Southern California.”

Paleoclimate data provide a foundation on which to build our understanding of our current and changing climate. Microfossils like the beetles at the La Brea Tar Pits hold the keys not only to our past but also our future. Not bad for some little bugs.


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