Flora magazine
The official magazine of the California Native Plant Society


Plants the Mammoths Ate

Vol. 5 No. 1

By David Bryant | Illustrations by Carly Lake

Across California’s landscapes, echoes of the ice age reverberate through native plants. the ghosts of extinct megafauna whisper through the blades and branches of plants that once provided food for thundering herds of Columbian mammoths, western horses, and the biggest camels ever known to exist. while these animals are gone, nearly everything they once ate continues to grow in the place we call California.

Researchers have delved into the ancient maws of Pleistocene animals to uncover incredible stories of Ice Age diets.

Plodding hoofs, sniffling trunks, giant maws, and prehensile tongues haunt our ecosystem. As you look out on the California landscape, some plants reveal evidence of past relationships with Ice Age creatures. Native plants with larger fruits, such as the fleshy pods of Joshua trees (Yucca brevifolia), once rode in Ice Age bellies that transported and deposited the seeds. The punishing spines of agaves and acacias likely fended off big, hungry mouths.

The spectacle of Ice Age creatures in our landscapes today would be a shocking and magical sight. But at the Rancho La Brea Tar Pits in the heart of Los Angeles, researchers uncover evidence of these Ice Age animals—and the plants they ate—on a daily basis. The most famous and plentiful Late Pleistocene deposit in the world, the tar pits have been capturing animals and plants in a gooey black substance called asphalt (not tar) for more than 50,000 years.

Animals waded into the asphalt-laden seeps of Rancho La Brea, becoming permanently mired. The first victims were often herbivores, followed by hungry carnivores. Plant fragments—pollen, twigs, leaves, seeds, fruit, flowers, and more—wafted in on the wind, plopped down from overhanging limbs, or were carried by streams or floods. Some may have even hitchhiked in the fur of Ice Age mammals. Researchers use the preserved remains of these animals and plants—from the nearly intact skeleton of a Columbian mammoth named Zed to the cones of extirpated Monterey pines—to piece together how California’s ecosystems have changed over time.


Columbian mammoths were the undisputed titans of the late Ice Age landscape. These behemoths were massive even for mammoths, weighing over 10 tons. Herds plowed through Rancho La Brea’s grasses and streams—each adult likely consuming over 400 pounds of plant material a day!

Each beast had four massive molars that were designed and implemented to shred through coarse grass and other abrasive material. Fossilized poop excavated from caves in Colorado show that grasses, sedges, and rushes comprised over 95 percent of their diets. They also ate prickly pear, sagebrush, maple, and blue spruce. 

What do the collections of Rancho La Brea tell us about our Pleistocene landscapes and the animals that dined on them? Although asphalt is a murky substance, new tools and techniques have revealed an ever-clearer picture of a changing world.

Many secrets come straight from the horse’s mouth (or camel’s, mammoth’s, or numerous other Ice Age creatures’). Over the decades, researchers have delved into the ancient maws of Pleistocene animals to uncover incredible stories of Ice Age diets as well as the general composition and health of the plant communities where these animals lived and fed.

Tiny abrasions and pockmarks on recovered teeth, called microwear, provide a picture of the foods that were consumed in an animal’s final days. Meanwhile, patterns of abrasion that build up over a lifetime, called mesowear, provide a picture of an animal’s overall food preferences. Chemical signatures called isotopes can offer a glimpse into the types of plants an animal ate. Microscopic particles of silica called phytoliths, which form in plants and can remain intact for eons, allow scientists to make informed plant identifications.


The Shasta groundsloth was an oddball with huge claws, a prehensile tongue, and hindfeet that turned dramatically inward. Fossilized poop from Nevada reveals that this quirky creature ingested vast amounts of Joshua tree leaves, fruits, and flowers. If that wasn’t painful enough, scientists have found intact agave spines in the animals’ poop. Softer globe mallow plants, with fuzzy leaves and beautiful flowers, also made their way through the groundsloth’s bowels. Based on these findings, the Shasta groundsloth appears to have been a fairly indiscriminate browser and took advantage of low-growing shrubs as well as any branch that its feisty claws could reach.

Dr. Regan Dunn, paleobotanist and assistant curator at Rancho La Brea, scratches the phytoliths off of prehistoric teeth to pinpoint the plant species an animal ate. Combined with these other lines of evidence, she and her colleagues have used the data to paint a more detailed picture of years, months, and even days within an Ice Age ecosystem.

Scientists at Rancho La Brea have found that over the course of 50,000 years, the local climate could be fickle, with droughts and spectacularly wet episodes, but trended along a U-shaped arch. Southern California was cooler and wetter until ~15,000 years ago. Wet conditions climaxed during the Last Glacial Maximum, a period when the world was at its iciest, and half of North America was under glaciers. As the ice receded, the climate warmed and dried.

During the cooler and wetter times, coastal Los Angeles would have felt like the Monterey Peninsula, with stands of the namesake pines. The fossil remains of a baby saber-toothed cat recovered in Carpinteria suggest that predators raised their young in these forests. Once ready for the hunt, prides of the fearsome cats turned east, where the forests thinned into a mosaic of shrubland and grassland dotted by groves of oak and juniper.


Today, camels are an emblem of Asiatic and North African deserts. But they first evolved in North America about 45 million years ago.

The western camel was one of the last species to roam the continent and ranged across the American West. It looked much like a dromedary camel, befitted with one hump, although its legs were slightly longer. Because of the grazing habits of modern-day camels and the high-ridged molars found in the fossilized remains—typically associated with a coarse, grassy diet—the western camel was written off as a grazer. But this assumption grazed over some key details. Studies of the microwear and mesowear on camel teeth, combined with isotype analysis and phytoliths, indicate that the species mostly browsed. Grazers are animals that eat a largely grass-based diet, while browsers typically feast on shrubs and trees.

At Rancho La Brea, meals likely included manzanita, California lilac, saltbush, oaks, and other browsable plants. The camels’ high-ridged molars likely evolved to handle the tough, coarse shrubs that define arid environments. So, while the western camel occasionally grazed on grasses, there’s a good chance that it also snacked on shrubs and reachable tree limbs.

It was this diverse, largely open environment with a mix of habitats— including seasonal waterways—that attracted massive game. Hordes of extinct camels, bison, mammoths, mastodons, and horses migrated through Rancho La Brea to feast and be feasted upon. Winged creatures found themselves trapped in the asphalt too, leaving behind the greatest collection of fossil birds in the world, including eight species of owls. The habitat preferences and diets of surviving owl species—such as the burrowing owl, barn owl, and great horned owl—suggest that Rancho La Brea was a mosaic of meadows and chaparral, dotted with groves and laced with seasonal creeks. These birds prefer open areas, flocked with woodlands, to perch and peer for their prey over the endless horizon.

Reading through the list of the more than 150 plants that fed the late Pleistocene in Southern California is like reading through a regional hiking guide of Big Sur: cypresses, pines, oaks, willows, sycamores, poison oak, manzanitas, and California lilac are just a few of the recognizable species we encounter today.

Over 50,000 years, plant communities flourished and faded, held fast and migrated. California junipers, the most common plant found at Rancho La Brea, did well during the cooler, wetter years of the glacial maximum. But about 13,000 years ago, as temperatures warmed and the climate got drier, they disappeared from the timeline, along with nearly all the other conifers in the area. Oaks enjoyed the wetter weather, but managed to persist as temperatures climbed. Reading through the list of the more than 150 plants that fed the late Pleistocene in Southern California is like reading through a regional hiking guide of Big Sur: cypresses, pines, oaks, willows, sycamores, poison-oak, manzanitas, and California lilac are just a few of the recognizable species we encounter today.

While the megafauna is gone, the plants have remained with us. As we look at the diets of three prehistoric creatures, you might be surprised by just how familiar the plants are.

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