First-Ever Fossil Poop Excavated From L.A.’s La Brea Tar Pits

La Brea Coprolites

Hundreds of exquisitely preserved mammal feces have been excavated from Los Angeles’ famous La Brea Tar Pits, with the potential to provide invaluable new clues about what Southern California was like in the late Pleistocene Epoch.

The droppings are the first confirmed coprolites, or fossil feces, ever reported from the tar pits.

“It’s incredible that after more than a century of excavation and study, we are still unearthing new types of fossils from La Brea’s treasure trove of deposits,” said Emily Lindsey, assistant curator at La Brea Tar Pits, in a press statement.

“These tiny finds may lead to big discoveries about the climate and ecosystems of Ice Age Los Angeles.”

The feces were first reported in 2016, after excavations had begun on a parking garage for the Los Angeles County Museum of Art next to the La Brea Tar Pits and Museum.

la brea tar pits corpolites
Fossil feces, and other plant material, from LA’s La Brea Tar Pits. (Photographs courtesy of Carrie Howard/Nature)

The abundance of tiny poop pellets were first thought to be the droppings of modern rats that had found their way into the seeps of natural asphaltum.

“We noted the occasional rodent fecal pellet in the processed matrix before, but it was easy to explain it away as modern contamination,” said Laura Tewksbury, senior preparator at La Brea Tar Pits, in the statement.

But as researchers kept finding more and more, they determined that the feces were prehistoric.

“We stared at the sheer number of pellets in silence for a minute, before looking at each other and stating, ‘There’s just no way that much is contamination,’” Tewksbury said.

Rather than being the droppings of modern rats, the coprolites are likely the remains of a huge Ice Age rat nest that had been subsumed by the creeping seeps of asphaltum, said Karin Rice, preparator at La Brea Tar Pits.

“The intact nature and density of the fossils require a taphonomic explanation other than entrapment,” Rice said.

“The preservation is more likely the result of an asphalt seep overtaking an existing rodent nest.” [Here’s another study based on La Brea specimens: “Ancient Cougars Survived Ice Age Extinction By Not Being Picky Eaters, Study Finds“]

In a paper published in Scientific Reports, researchers led by La Brea Postdoctoral Fellow Alexis Mychajliw analyzed hundreds of the pellets, and their findings provide some initial glimpses into what life was like in L.A. in the Late Pleistocene Epoch.

Judging by the size and shape of the poop, as well as the abundance of well-preserved plant material found around it, researchers think the droppings are the work of a pack rat, or wood rat, belonging to the genus Neotoma.

And pack rats’ famously big, messy nests are prized by scientists, because they often contain hundreds of years’ worth of environmental data in them, in the form of plant material.

In fact, government scientists actually maintain a database of more than 3,000 ancient middens recorded around the country that together provide a snapshot of climate and ecology throughout recent history.

In the case of the La Brea rat droppings, samples were radiocarbon dated to about 50,000 years ago, when much of northern North America was still iced over.

But downtown Los Angeles was still balmy, if cooler than it is today.

Earlier research on insects found at La Brea suggest that temperatures were within about 5 degrees Celsius of today’s temps.

And studies done on the poop confirm this.

The team analyzed carbon isotopes in the feces, which show that the wood rats ate more of what are known as C3 plants, like trees and shrubs, which typically grow in cooler, wetter regions than C4 plants, like grasses and sedges, which typically grow in warmer climes.

Some direct evidence of these cool-weather plants, like oak leaves, were also found in the tarry nest.

These long-overlooked trace fossils provide a wealth of opportunities for future research into La Brea and other Pleistocene sites, Mychajliw said.

“This nest provides an unparalleled view of what was beneath the feet of Rancho La Brea’s famous megafauna,” she said. [Learn more about La Brea’s fossil finds: “Saber-Tooth Cats, Dire Wolves Found in La Brea Tar Pits Show Wounds From Ice Age Battles”]

“And to me, it emphasizes the importance of studying small mammals, too.

“Woodrats survived the Ice Age and still build nests in local urban green spaces like Griffith Park!

“By studying these nests, we have a direct line from the past to the present through which to trace human impacts on Los Angeles’ nature over time.”

Citation: Mychajliw AM, Rice KA, Tewksbury LR, Southon JR, & Lindsey EL. (2020) Exceptionally preserved asphaltic coprolites expand the spatiotemporal range of a North American paleoecological proxy. Scientific reports, 10(1), 5069. PMID: 32193515

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