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The [Fossil] Treasure of the Sierra Nevada

The Sierra Nevada mountain range is known for its gorgeous alpine lakes, magnificent peaks, and glacier-carved valleys. It’s home to five national parks and monuments, and the only place in the world you can see giant sequoias.  In various places, the peaks above hide an extensive cave system below. Some of these caves house a scientific treasure trove of fossils, and this summer the University of California Museum of Paleontology (UCMP) is using them to uncover the long-term record of California climate change.

The living vertebrates of the Sierra Nevada have been studied by Berkeley scientists for over 100 years. In 1911, Joseph Grinnell (director of the Museum of Vertebrate Zoology, or MVZ) began surveying  Yosemite National Park and Sequoia National Forest. These surveys were pretty intense, especially for that time: the Yosemite Survey alone required an incredible 957 person-days of fieldwork (the equivalent of one person working around the clock for almost three years). Over 4000 specimens were collected in Yosemite alone, accompanied by 3000+ pages of field notes and 700+ photographs (Moritz et al. 2008). The notes and photos are so detailed that the specimens can all be traced to their exact collection location. In other words, we have an extremely good record of which vertebrates were hanging out in the Sierra Nevada 100 years ago, and exactly where they were living.

Yosemite Transect
Joseph Grinnell’s original (1914-1920) transect of Yosemite National Park in the Sierra Nevada, eastern California. (c) Museum of Vertebrate Zoology, accessed here.

How does that compare to what lives there today? With support from the National Science Foundation (abstract here), MVZ researchers resurveyed Grinnell’s original collection sites to find out. Their results were shocking: half the species showed significant range shifts (Moritz et al. 2008). Higher-elevation (cold-dependent) species shrank their ranges to isolated mountaintops. Formerly low elevation (warm-tolerant) species now lived higher on the mountainside, but no longer at the base. If a temperature increase of just 3°C over 100 years affected so many species, what happens when mountaintops are no longer tall enough for animals to escape the heat? This could mean big trouble if global temperatures rise even just a little more.

But what if this was all a quirk? How would you know if the last 100 years indicated an alarming new trend, a weird century, or a return to normal?  The answer is simple: we can’t know until we can link the modern record to the fossil record.  In a previous post, I mentioned that paleontology puts the living world in context. It allows us to understand the relative magnitude of changes happening in today’s world. Paleontology unlocks context much farther back in time than we get from studying the modern record alone, even when the details are really good (like the MVZ’s Sierra surveys).

Fortunately, at Cal we have the Berkeley Initiative in Global Change Biology, whose goal is to bring about exactly that type of data integration. BIGCB brings together all sorts of researchers who study the effects of climate change on past, present, and future life. Together, these groups can address and answer questions at larger scales than any one team could address on their own. All of the Berkeley Natural History Museums are sharing data, as well as the University of California field stations, reserves, and experimental forests. Thus, our fossil data is integrated with that of specimens collected in historical times, in addition to ecological and climate data, information from lab experiments, and computer models.

Melissa is one of several UC Berkeley undergrads helping to catalog the Crystal Cave site.
Melissa is one of the UCMP’s elite team of undergrads helping to catalog Pleistocene fossils from California.

This summer at the UCMP, there’s a major push to identify and catalog undescribed material from the relatively recent fossil record of California, especially in areas where we have a great record of change on the 100-year scale. Ultimately, we want to compare the 100-year trend to what we see at the the 1000-, 10,000-, and 100,000-year scales. Dr. Pat Holroyd, one of the UCMP’s museum scientists, is supervising a team of Berkeley undergrads who are identifying and cataloging of fossils from the California Pleistocene (the geologic epoch that lasted from ~2.6 million to 11,700 years ago). They’re starting in the Sierra Nevada, at a site called Crystal Cavern 1. This cave site is in El Dorado County, about halfway between the MVZ’s Yosemite Transect and its Lassen Transect.

The caves under the Sierras and their foothills are pretty recent, geologically-speaking.  Stock (1918) estimated nearby Hawver Cave to be Rancholabrean (11,000-240,000 years old) based on the fossils he found there. We don’t yet know exactly how old the Crystal Cavern 1 fossils are, because we have not yet attempted to date them using radiometric methods. This would be a great project for an interested undergraduate or graduate student!

How did the fossils get there? Sometimes, animals fall into or get lost in caves, and they die before they can find their way out. Or they can be washed in when surface waters drains into the caves. There are a lot of underground rivers in the Sierra caves, and their normal ebbs and flows can build up concentrated deposits of bones over time. Pat says that based on the original description of the locality, the fossils were preserved in a layer of mud capped by flowstone. A lot of the specimens still have this mud and flowstone on them; this is usually cleaned off before they are put in boxes in our collections.

skunk jaws
These are jawbones of the striped skunk, Mephitis mephitis. The top specimen is bone from an animal collected by UCMP scientists in the last 100 years. The bottom two specimens are newly-cataloged fossils from Crystal Cavern 1.

The team has only been working for a week, and already they’ve sorted, identified, cataloged, and curated over 350 bones. If you’re interested in tracking their progress this summer, you can see a list of specimens at the Crystal Cavern 1 locality as they get added to the UCMP database here.

I asked Pat to show me some of the Crystal Cave specimens that she and the undergraduates identified, and she gladly obliged.  The site is definitely dominated by the small mammals that Shaena recently explained were so important to understanding climate change. As you might expect from a relatively recent fossil site, most of the fossils are from species that are still alive today, some of which still live in the area. Pat showed me a lot of mammal bones; these include striped and spotted skunks, wood rats, deer mice, squirrels, mule deer, and even mountain beavers.  There are a number of birds (including owls and California quail), and even a tiny lizard jaw. But there are also some extinct animals in the mix. The largest compare well to the extinct shrub-ox Euceratherium, fossils of which have never been discovered in the Sierra Nevada.

Other interesting finds include bones with tiny tooth marks where little rodents nibbled on the remains of larger vertebrates. I include a photo  below, because it’s so cool to see evidence of fossilized behavior, like scavenging:

Tiny rodent tooth marks are visible on the edge of some of the Crystal Cavern 1 fossils.
Tiny tooth marks are visible on the edge of some of the Crystal Cavern 1 fossils, like this mule deer jaw (click for larger image).

What I like most about this team is that it’s so diverse academically – we have history and psychology majors getting hands-on experience generating scientific data alongside our biologists. Even if they don’t go on to become scientists, they’re getting a first-hand understanding of what the process of science is like: where the data come from, what it takes to acquire it, how we test our ideas, and how individual pieces of data contribute to a larger research question. Best of all, Pat told me that at the end of the summer, the undergrads are going to help her write a scientific paper describing the Crystal Cavern 1 fauna. Our students are not only contributing to a better understanding of how an ecosystem changes with climate and time, but they’re contributing original research to the scientific literature. Everyone wins!

Our crack team of undergrad catalogers is being funded by the W.M. Keck Foundation, who in 2011 awarded UC Berkeley a $1.5 million grant to integrate data from UC Berkeley’s natural history museums, field stations, and labs (abstract here). The broader research initiative is also funded in partnership with the Gordon and Betty Moore Foundation, with seed money from Berkeley’s Office of the Vice Chancellor of Research (read more about BIGCB funding here). I tip my hat to all three organizations for understanding the importance of museum collections in addressing big picture questions about things like climate change. The sooner we integrate the modern and fossil records, the sooner we can sort out how big a change we’re dealing with.

Stock C. 1918. University of California Publications (Bulletin of the Department of Geology) 10: 461-515. Read the whole volume for free here!

Moritz C et al. 2008. Science 322: 261-264. You can also connect with MVZ Curator Jim Patton on ResearchGate and get it here.

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