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50,000 years of Los Angeles summers?

Courtesy of the Natural History Museum of Los Angeles County

Concept: Scientific knowledge is open to question and revision as new ideas surface and new evidence is discovered.

One doesn't always have to leave the city to find fossils. Paleontologist Anna Holden works smack dab in the middle of Los Angeles studying insects (some 50,000 years old!) excavated from the Rancho La Brea Tar Pits. She uses data on the temperature and moisture needs of those bugs to figure out what the climate of the Los Angeles Basin must have been long before humans arrived and began sweating through traffic jams. While other work suggests that the saber-toothed cats sucked into the tar inhabited a wetter, cooler version of Los Angeles, her research points to a different interpretation. She explains,

I noticed that climate reconstructions of LA were often based on organisms that are not ecologically sensitive — for example they can live in many types of habitats and climatic ranges. Or, if they are restricted to local environments, they hadn't been analyzed with modern methods that would extract the necessary data. In contrast, when I started looking at all the insects found at the Rancho La Brea Tar Pits, I thought that the climate being significantly colder and much wetter doesn't make any sense.

Multiple species of ancient La Brea insect fossils are plentiful, and can be individually dated — and all happen to be species that live in warm, dry, Mediterranean habitats, much like the Los Angeles we know today. As more and more data are collected, the weight of the evidence seems to be shifting to support the idea that the LA heat is nothing new. However, many of these species may soon be pushed to their ecological limits by modern climate change.

Just a few of the insect fossils from the tar pits that Anna studied. Photo courtesy of Anna Holden. Scale bar = 0.5mm. Left to right starting at top left: Helophorus sp. (Helophoridae), Peltydotes callosus (Haliplidae), Staphylinidae cf. Xantholinini, Sitona sp. (Curculionidae), Hyperaspidium cf. minima (Coccinelidae), Dicheirus dilatatus(Carabidae), Hyperaspis sp. Fimbrolata group (Coccinelidae), male Tapinoma likely schreiberi, maybe sessile (Formicidae), Bembidion semipunctatum (Carabidae),Rhyparochromidae, Olla sp.(Coccinellidae), Coelambus cf. masculinis (Dytiscidae), Piesma sp. dorsal (Piesmaidae), Piesma sp. ventral (Piesmatidae), Diabrotica undecimpunctata (Chrysomelidae), Tenebroides crassicornis (Trogossitidae), Euspilotus sp. (Histeridae), Formica moki (Formicidae), Alticini (Chrysomelidae), Necrobia violacea (Cleridae), Uroctonus mordax (Scorpiones: Vaejovidae), Neoheterocerus gnatho (Heteroceridae).)

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