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.
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!
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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