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The Tar Pits are Filled With Ice Age Survivors

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Tar pits tableau | Photo: Onasill ~ Bill Badzo, some rights reserved

In 1970, from the gooey depths of Pit 91, an unknown excavator found the most beautiful fossil ever extracted from the La Brea asphalt seeps. The Pleistocene remnant wasn’t a sabercat tooth, dire wolf jaw, sloth claw, mammoth femur, or anything at all like the megafauna that have made the bubbling and belching spot off Wilshire Boulevard famous. It was just a little nub of plant material that was eventually cataloged as part of a bee nest and forgotten for decades until paleoentomologist Anna Holden took a new look. The nest structure was unmistakable – the capsule had been made by leafcutter bees, never seen at La Brea before, and high-resolution scans revealed intricately-preserved pupae still inside. The Ice Age insects are the most delicate creatures to ever emerge from the tar, but their beauty goes beyond aesthetics. The immature bees belonged to the species Megachile gentilis – a species still alive today that connects La Brea’s ancient past to its urban present.

Death at both large and small scales looms large at La Brea. Visitors pass by the somber tableau of a mammoth trapped in asphalt, trunk haplessly raised to the sky as baby and herdmate look on, to a museum filled with the chocolate-colored bones of species that have been extinct for over 8,000 years. These are the celebrities of the recently-rechristened La Brea Tar Pits and Museum – snarling Smilodon, slinking dire wolves, burly short-faced bears, enormous camels, and the imposing, condor-like teratorns, each a monument to both paleontological persistence as well as catastrophe that is as hotly-debated now as when the sudden loss of North America’s megafauna was first recognized. But there are stories of survival, too. Whether it was climate change, human hunters, or, more likely, a combination of the two, the environmental changes at the end of the Pleistocene did not wipe the ecological slate totally clean. Many of the species found in the tar pits are still alive today, and they’ve been able to carve out a living in their old haunts even as Los Angeles has sprawled across the landscape.

You can see some of these survivors in the tar pits museum itself. They’re easy to miss, hidden in an alcove after all the more charismatic megafauna have been put on parade. Tucked away to the side is the skeleton of a golden eagle perched above the head of a bony coyote. Both are found by the hundreds in La Brea, and both still make LA their home. Not that these species have remained static since the days of the mammoths and mastodon. For the coyotes, especially, the disappearance of the more massive La Brea residents forever changed the west’s clever and ubiquitous canid.

La Brea’s fossil coyotes have long been known to be different than their modern counterpart. John Campbell Merriam, one of the site’s pioneers, noticed the difference a century ago, but this was generally thought to be a quirk of climate. Cooler past temperatures would have given bigger coyotes a better ability to regulate their body temperature, and this seemed so obvious that no one paid much attention to the carnivores. When fossil carnivore expert Julie Meachen started to look at the coyotes anew, however, she found something very different. Competition, not climate, is what gave the ancient coyotes their size.

The crucial clue came not from the coyotes alone, but from comparison with wolves. Gray wolves, while not as numerous as their dire cousins, were present in southern California during the Pleistocene, too. So if climate were responsible for changing size, Meachen reasoned, then the wolves should have shrunk as the world warmed. But they didn’t. Gray wolves stayed the same as coyotes shrunk. And this hints at something unexpected. “Pleistocene coyotes were larger and more robust than their modern counterparts,” Meachen says, and additional research has suggested that “they mostly likely would have traveled in larger groups than living coyotes, maybe more like wolf pack sizes.” With so many other carnivores on the landscape, coyotes had to be bigger and coordinate in order to get their share.

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Coyote skeleton at the Page Museum | Photo: Eden, Janine and Jim, some rights reserved

Why coyotes survived while so many other carnivores perished, though, is unclear. Coyotes are extremely adaptable, Meachen says, and the canids have certainly adjusted to making a living as our neighbors even in cities. But they have just made it through by the skin of their teeth. “Through DNA analyses we are learning that many mammal species almost went extinct at the end of the Pleistocene,” Meachen says, “and I think coyotes are no exception.”

For so long, the focus on the Ice Age has been on what was lost. Sabercats and mastodons have a strong hold on our imagination, not to mention that our own possible involvement in the Ice Age extinctions is the prehistoric frame for the current biotic crisis. But Meachen and other researchers are adding to a burgeoning area of research that looks at Pleistocene survivors and what their histories can tell us about life, death, and evolution over thousands of years. In another recent study, for example, paleontologists Larisa DeSantis and Ryan Haupt determined that La Brea’s cougars were probably able to survive because they had a more generalized diet than the other big cats of the time. Without that flexibility, P-22 wouldn’t be roaming Griffith Park today. And given that the La Brea collections contain ornate shrews, broad-footed moles, pallid bats, black-tailed jackrabbits, eastern spotted skunks, black bears, lynx, and more, there’s a wealth of connections waiting to be made between past and present. This goes way beyond mammals, of course. La Brea has also yielded 139 species of birds, 116 of which are still alive today, as well as 158 species of plants from junipers that grow locally to coast redwoods that were wiped out locally but still exist elsewhere.

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Leafcutter bee capsules from the tar pits, with a modern one at lower right | Image: PLOS ONE

In fact, it’s some of these smaller stories that help flesh out what La Brea was like back when Smilodon was still prowling around. Without the plants, invertebrates, and often-overlooked cast members, the megafauna would just be walking around on a blank stage. It’s the meek and mild species that can still be observed today that allow paleontologists to peer into the lost world, insects most of all.

La Brea’s invertebrate collection is enormous. The museum’s official website lists over 100,000 arthropods alone, although Anna Holden says she “cannot even imagine how many insects there are at the tar pits.” Much of that material, though, isn’t as pretty as those little leafcutter pupae. While there’s a wealth of material, Holden says, most are “disarticulated black bits” that are challenging to work with. Still, with persistence, many of these scraps can be identified down to species, and that’s because almost every single insect species at La Brea is still alive today. The bees, the beetles, and more can all be observed, and this has given Holden and other paleoentomologists insights that just can’t be gleaned from bones alone.

By looking at the habits of living representatives of species found in La Brea, Holden says, she can see how closely each insect was tied to certain habitats and temperatures. There’s a La Brea beetle, for example, that can’t stand rainfall. “It’s found in grasslands, in pretty dry, arid, warm to hot regions with no precipitation,” Holden says, and this seems to hold for the insect community as a whole. “I’ve been struggling to find an insect at the tar pits that likes cool, mesic conditions, that likes precipitation,” Holden says. Part of this may be the bias of fossil record, Holden notes. The tar just isn’t as sticky when it’s cool, so maybe those insects just didn’t get trapped. But it’s also possible that La Brea has always been a warm, dry place, the insects tracking what the world was like. “I’m looking for proxies, for senses of indicators,” Holden says, and insects, more than any bird or mammal, can do that.

To envision Columbian mammoths and American lions wandering southern California takes a stretch of the imagination. They seem as distant as the non-avian dinosaurs, inhabitants of a time that we can touch but can’t see. And yet their time was practically yesterday, and not all of the Pleistocene is lost. The mountain lion taking a catnap in the hills, the leafcutter bee building a nest in your yard, the golden eagle looking down on highway traffic are all the still-evolving tethers to the Pleistocene’s lost world.

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