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Q&A: Meet a paleontologist unearthing Ice Age fossils in future Purple Line stations

“We’re anticipating a wealth of fossils near the tar pits”

Researchers excavating tusks
In November, Leger and her team unearthed the skull of a young mammoth below Wilshire Boulevard.
Photos courtesy Metro

One of the pluses of building a subway network in a city with a rich geological history like Los Angeles is that, as crews work to excavate future stations, they often stumble upon ancient artifacts from the area’s past.

With work underway on the Purple Line extension to Westwood, Metro has contracted paleontologists to identify and extract fossils turned up during excavation below Wilshire Boulevard. So far, they’ve found the remains of a young mammoth and a prehistoric camel, among other exciting specimens. The fossils will eventually be turned over to the Natural History Museum of Los Angeles County.

We caught up with Ashley Leger of Cogstone Research Management, the firm handling paleontological work on the Purple Line. Leger oversees a team of monitors who accompany construction workers during excavation, identifying any fossils that may be unearthed as the extensive subway line is built.

We talked to Leger about her work, recent finds, and prehistoric Los Angeles. This interview has been edited for length and clarity.

How often do you make a find?

You know, fossils are actually very rare, so our finds are few and far between. We estimate that less than 1 percent of life on earth actually fossilizes, so fossils in any instance are incredibly rare.

We seem to find something every couple months. There’s usually a lull, and then a couple things are found. We’re at a month and a half now without finding anything, so I’m expecting a phone call any day.

Do the types of fossils you expect to find change depending on where you’re digging?

Yes. As we progress deeper, the sediment becomes older. While we’re in the Pleistocene—or the Ice Age—material, we’ll be looking at that classic tar pit fauna: mammoths, mastodons, saber cats, horses, and things of that nature. Once we get below that, we’re going to be in the marine sediment, and then we have potential marine animals. I’m still hoping for a whale skull.

Given the close proximity to the La Brea Tar Pits, is the Purple Line likely to be a more fossil-rich area than other parts of LA?

We’re anticipating a wealth of fossils near the tar pits because of the asphalt deposits. That asphalt, or that tar, creates a natural trap, and then the tar also helps seal the bones and preserve them for the future. So the more asphalt we encounter, the better off we are for finding fossils because it aids preservation.

Painting of saber cat and sloths around a stream
A restoration by Charles R. Knight detailing what the area around the La Brea Tar Pits may have looked like during the Ice Age.
Wikimedia Commons

What kind of fossils end up in asphalt deposits?

Typically, we find more of the prey type animals. The predators are few and far between. That’s because there are less predators that live in a given area—they have to have an abundance of things to eat.

But in the tar pits, you have the reverse situation. Paleontologists there are finding more predators than they are prey, because of the tar. That prey-type animal gets trapped, it trumpets for its friends, and then all of the predators in the area are alerted that something’s in distress.

You can insert any animal—camel, horse, bison, mastodon. Those animals get stuck in that tar, and their first reaction is to panic. Because they’re not used to anything that’s going to grab at their feet. They’re used to walking along and eating grass all day. So when something in that situation changes, they automatically panic. So they do two things: They struggle, and they call out for help.

If it’s a camel, the rest of the camels come over to see what’s happening. Then the animal falls over and has tar on more of its body, so it panics more and trumpets even more loudly. And at that point, every dire wolf in the area, and every saber-toothed cat perk their ears up and they think, “Something is struggling, this is an easy meal. Let’s go get it.”

So then they come, they jump on top, thinking it’s an easy meal, then all of a sudden, their feet are stuck. So they trumpet for help, and more and more predators come. Eventually you have an asphaltic deposit where it’s bone on top of bone of every species you can imagine.

What would Ice Age-era Wilshire Boulevard have looked like?

We’ve got a pretty good glimpse of what the landscape looks like, particularly because we’re so close to the tar pits and they’ve done so much analysis on plant material and pollen and bugs. So we have a pretty good idea of what Los Angeles looked like.

What’s interesting for us is that we can tell we’re in some sort of water situation. From the sediments we’re looking at, we know we’re in a small stream or pond setting—which makes sense for how many animals came near. They’re in the area because there’s water available.

The landscape would have had some trees, probably in little groves. But a lot of it would have been open grassland, with thick, green, tall vegetation. It’s hard for us to imagine, because it’s such a packed area. It’s hard to think, okay, remove all these buildings and put in wide open grasslands, and add a herd of mammoths and a herd of horses and add a herd of bison. Then picture that saber cat stalking them.

It’s challenging to wrap your brain around, but it really does tell a story. We know that it was open and it was abundant, because we’re finding so many fossils in the area. It was just teeming with life.