Listen to Episode 67 on PodBean, Spotify, YouTube, or your podcast source of choice! And don’t forget the Bonus Episode: Voices of La Brea!
Join us as we explore one of the most famous fossil sites in the world. It’s not in a desert or on a mountain, but in the heart of one of the largest cities in North America. It’s also one of the best places on Earth to understand the changes in climate and ecology at the very end of the Ice Age. This episode, we take a trip to the La Brea Tar Pits.
In the news
A new species of very successful (and spaceship-like) Cambrian predator.
Early evolution of turtle bone structure.
In mammal ancestors: the evolution of a tiny bone that makes us mammals.
A new fossil whale and the invertebrates that destroyed its bones.
The La Brea Tar Pits
Once you make it through the Los Angeles traffic, the La Brea Tar Pits are among the most accessible fossil sites in the world. Located in Hancock Park, they attract paleontologists who come to preserve and study the incredible assemblage of Ice Age fossils, as well as visitors who can peek in on the work the crew is doing.
The fossils here date to the Late Pleistocene, mostly between 50,000 and 10,000 years ago. This range covers the last major glaciation event, the famous megafaunal extinctions, and the arrival of humans in the region, which makes La Brea a great source of information on ecological evolution. And beyond that, the amount of fossils found here is staggering.
A 1992 census counted around 3.5 million specimens in the La Brea collections, including around 650 identified species of plants and animals collected over the past century. Their fossil bird collection alone contains around 250,000 specimens of around 140 species, their insect collection includes members of 25 different insect families, and many of their large mammal species are known from hundreds and even thousands of specimens.
It’s asphalt!
Deep below Los Angeles, there are Miocene-aged deposits of oil-rich ocean sediments. In some places, fissures in the earth allow oil and gas to seep upward, eventually emerging on the surface to form a thick, sticky substance: asphalt.
This asphalt spreads across the ground in thin layers, where it acts like flypaper. Anything that contacted it – from seeds to spiders to saber-toothed cats – might get stuck, unable to escape. As this asphalt mixes with other sediment and builds up layer by layer, it collects thousands of years of material. (So, it’s not really “tar,” which is more fluid, and it wasn’t forming deep pools like the common image.)
Because it traps organisms this way, La Brea functions as a “predator trap.” Big Ice Age carnivores would be drawn in by struggling or recently-dead prey and then become stuck themselves trying to get to it. This is why, among the big mammals in the fossil assemblage, carnivores outnumber herbivores 9 to 1.
From Native Americans to more modern civilizations, humans have long used La Brea as a source of glue material and oil. Fossils were first documented in the area in 1875, excavations began in earnest in the early 1900s, and that work continues today. You can go see it at the park!
Learn More
The website of the La Brea Tar Pits & Museum includes great information on the site’s formation, history, collections, and more. (Non technical)
Check out the ongoing research at the site. (Non-technical)
The 2015 volume, La Brea and Beyond: The Paleontology of Asphalt-Preserved Biotas, includes info on the site’s history and recently-published research. (Technical)
Here’s some very recent research on the diets of La Brea’s big predators. (Non-technical)
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If you enjoyed this topic and want more like it, check out these related episodes:
- Episode 137 – Fossilization
- Episode 25 – The Pleistocene Megafaunal Extinction
- Episode 32 – Naracoorte Caves, Australia
- Episode 94 – Dogs
- Episode 93 – Cats
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COMMON DESCENT 
I greatly enjoyed this episode, La Brea is such a special site! The wall of dire wolf skulls took my breath away the first time I saw it, I had no idea there were as many as 10x more individuals than that display!
I have one tangential question. Near the end of the episode a book by Walter Alvarez was mentioned, “T.Rex and the Crater of Doom.” I was just wondering, do you give any credit to the claims of Gerta Keller, namely that the Chicxulub impact event may have predated the K-T extinction and that the Deccan traps (a large area of supervolcanic activity in India) are perhaps more to blame for the fifth mass extinction?
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Hi Trevor! Thanks for listening!
As far as we know, Keller has been proposing a disconnect between the Chicxulub impact and the K-Pg extinction for many years, but the idea hasn’t really found broad support in the scientific community. We think it’s very likely the Deccan traps played a part in the extinction event, but very unlikely that the impact didn’t. Paleontologists who study the K-Pg (the ones we’ve heard from anyway) generally think the impact had the biggest … well, impact.
We also discuss the K-Pg Extinction in Episode 5!
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