San Nicolas Island is a strange, far-away place very familiar to a surprising number of Californians. Thanks to Scott O'Dell's Island of the Blue Dolphins, this island — the most remote of California's eight Channel Islands — and it's native Nicoleño people have been engrained into the imaginations of many elementary school children. My own mind was captivated by this story in the fourth grade when I had the opportunity to conduct fieldwork on San Nicolas Island with Daniel Muhs (U.S. Geological Survey) and my adviser Seth Finnegan in July 2015 I was thrilled! Descending from hundreds of feet above the island’s landing strip I was already able to spot the very reason for my fieldwork- Pleistocene fossil beaches.
San Nicolas Island from above showing its terraced coastline. Marine terraces - records of ancient beaches - are formed by the powerful erosional energy of waves. They are relatively flattened geomorphological features that can serve as convenient pre-leveled platforms for human infrastructure. Hence, San Nicolas Island’s naval base airstrip (the island has been a naval base since the 1940’s) lies atop the island’s seventh terrace, which is the island’s most apparent marine terrace. Photo by D. Günther
Emily standing on a concretion jutting out just below San Nicolas Island’s youngest marine terrace (~80,000 years old). Photo by Seth Finnegan
Carved by the powerful energy of ancient waves, over 11 Pleistocene fossil beaches are terraced (hence their geological name "marine terrace") over the landscape of San Nicolas Island's modest 23 square miles. The youngest fossil beach (~80,000 years old) sits just above present-day sea level and the oldest (~1,200,000 years old) lies atop the island's highest elevation. Fossil mollusc shells — very similar to the kinds you find along California beaches today — abound within these marine terraces. Differences in the species compositions and abundance of these mollusc shells record dynamic ecological changes that occurred in response to glacial-interglacial climatic change during the Pleistocene.
Close-up of marine terrace sediments from one of the island’s oldest marine terraces (~1,200,000 years old). Fossil preservation on this terrace is exceptionally good- with original shell color preserved on many specimens.
My goal on San Nicolas Island is to collect fossil shells from the lowest three marine terraces — which record the last full interglacial cycle (~120,000 – 80,000 years ago). In particular, I am collecting well-preserved fossil Callianax biplicata (common name, purple olive shell) specimens. Using these fossil shells, I am reconstructing paleoenvironmental conditions during the last interglacial period through the use of stable isotopes. The reason this is possible is because shells grow by semi-continuously depositing layers of calcium carbonate. In the same way scientists use tree rings to chronicle the life a tree, I am using shell growth layers to reconstruct the environmental conditions experienced during the lives of molluscs that lived during the last interglacial period.
After collecting fossil C. biplicata from the terraces of San Nicolas Island, Sydney Minges (UCB Integrative Biology and Earth Planetary Sciences undergraduate student) and I sampled tiny holes along shell growth lines and analyzed these samples for carbon and oxygen stable isotope ratios at UC Berkeley's Center for Stable Isotope Biogeochemistry. Taken together, these isotope ratios can be used to reconstruct changes in seasonal, annual, and inter-annual seawater conditions and temperature during the last interglacial period. When combined with paleoecological species abundance and composition data, these paleoenvironmental data will allow me to test whether species lived in environmental regimes during the last interglacial period that are quite different from conditions they experience today, or whether species have tracked their environmental niches from the last interglacial period to the present day.
Left: Emily sampling fossil C. biplicata (purple olive shell) from a terrace on San Nicolas Island; the majority of white shells in photo are C. biplicata specimens. Photo by Seth Finnegan. Top Right: C. biplicata modern shell (specimen in ~1 cm in length). C. biplicata are the most abundant shells on both modern and Pleistocene beaches in southern California. Bottom Right: Sectioned fossil C. biplicata shell; small holes along right side of shell are spots that are being sampled for stable isotope analysis. Photo by Sydney Minges.
San Nicolas Island is only one of my dissertation study areas. Ultimately, I hope to reconstruct the paleoenvironmental and paleoecological conditions of the last interglacial period along much of the coast of southern California. The uniqueness of this Channel Island's geology and biota will leave a lasting impression. Aside from its extensive marine terraces and rich archaeological record, San Nicolas Island also boasts ghostly caliche forests, adorable dwarfed gray foxes called "island foxes", and some of the most pristine rocky intertidal habitats in southern California. Through my work reconstructing the paleoenvironmental and paleoecological characteristics on San Nicolas Island and elsewhere in southern California, I hope to establish a pre-human baseline for how shallow marine environments respond to climate change.
Emily and Dan Muhs on a marine terrace with abundant Giant Coreopsis plants. Photo by Seth Finnegan.
Island fox on San Nicolas Island. Island foxes are dwarfed relatives of mainland California’s gray fox. Adult island foxes weigh about 4 pounds. Photo curtesy of the Island Conservancy.
Caliche forest that dates to the Last Glacial Maximum; fossil root casts- many of which are Giant Coreopsis- are visible. Caliche is a sedimentary rock made of calcium carbonate cement. Photo by Emily Orzechowski.
Intertidal sea urchins living in holes bored into Eocene sandstone on San Nicolas Island.
This work is generously supported by grants from The UC Museum of Paleontology, National Sigma Xi, Berkeley Chapter of Sigma Xi, The UC Berkeley Department of Integrative Biology, The Evolving Earth Foundation, The American Philosophical Association, the American Association of Petroleum Geologists, the American Museum of Natural History, and the Geological Society of America.
As an English major, I didn’t really know what to expect when I first started my URAP (Undergraduate Research Apprenticeship Program) appointment for the UC Museum of Paleontology Fossil Insect PEN (Partner to an Existing Network) funded by the National Science Foundation. All I knew was that I’d be handling fossils, and that struck the scientific chord in my imagination in perfect harmony.
Meschelle Thatcher (left) examining the uncatalogued McKittrick bulk asphalt samples for beetle remains and her finds (right).
The Pleistocene Rancho La Brea tar pits in southern California are best known for their extinct exotic animals. However, I’ve learned there is more life in these asphalt seeps than saber-toothed cats, dire wolves, sloths, mastodons and camels. As part of my URAP experience I’ve been sorting the remains of beetles from the asphalt seeps at Rancho La Brea in Los Angeles and those near McKittrick, CA, in the southern San Joaquin Valley. Again, coming from a Humanities-oriented framework, I was slightly overwhelmed when my supervisor, Senior Museum Scientist, Diane Erwin, told me to pull out all the beetles I could find from bulk samples of asphalt recently discovered in the collection that had not yet been catalogued. Surely I was capable of spotting beetles, but I found myself wondering if I should also put aside things that look like legs, fragments of elytra and other beetle body parts? What if these beetle remnants should somehow alter the course of science forever? Ultimately, I found out that these anatomical fragments were indeed cute, but it wasn’t necessary to catalog them as individual specimens. Although not deserving of their own photo shoot, I learned they would be gathered for a group photo.
Meschelle carefully preparing type specimens for their photo session.
Fast forward to this lovely week in April, and I now have plenty of whole beetles really worth looking over. While most of them were easy to spot with the naked eye, I sometimes had to use a 10x magnifying glass to find the really small ones mixed in with the asphalt—the struggle with which I am positive any real paleontologist will identify. Undoubtedly, analyzing these fossils via zoomed in images of them will be particularly helpful. After all, the naked eye can only see so much. And when some of the beetle remains are just a few millimeters in size, we wholeheartedly welcome technology to swoop in and save the day . . . so long as we get the credit for our discoveries.
I have also helped with the imaging of the UCMP type specimens from Rancho La Brea and uploaded several dozen photos of the McKittrick beetles in the effort to digitize the diverse fossil insect collection at UCMP. By doing so, researchers, teachers, students, as well as citizen scientists and interested public all over the world will literally have accessible data at their fingertips to study. The Rancho La Brea type specimens, described and illustrated over 100 years ago, are a wonderful example of how the digitization age is allowing us to see these old collections in a new light.
As I move forward in this project, I will keep you updated about both my progress as an amateur paleontologist and my progress as a lifelong learner of interdisciplinary interests.
By Marianne Brasil and Tesla Monson posted February 29, 2016
Mrs. Charles Camp and her son, Charles Camp Jr., in South Africa (1947-48).
At the time we got involved in what has now become for us - the South Africa project - one of us (Tesla) was soon-to-be a second year graduate student, and the other (Marianne) was about to start her senior year as an undergraduate student here at UC Berkeley.
We began working together in the UC Museum of Paleontology (UCMP) during the summer of 2013, making our way through a massive project and cataloguing exceptional fossil material collected during the UC Africa Expedition of 1947 and 1948. This is the story of that project and the journey that followed.
The UC Africa Expedition
A bit of background for those who may not be familiar with this aspect of UC Berkeley history… as World War II ended, a massive research expedition, dubbed The UC Africa Expedition (UCAE) was just beginning to pick up steam on Berkeley campus. From 1947-1948, the extensive research endeavor became an influential force across numerous fields of study.
During this time, the Expedition also attracted plenty of media attention, resulting in dozens of newspaper articles that were published while the expedition was underway. There were two separate branches of the expedition: the northern branch (led by Wendell Phillips) and the southern branch (led by our very own Charles Camp, director of the UCMP from 1930-49). In addition to all of the fossil material that is now housed in the UCMP, the UCAE brought back an enormous amount of material that, to this day, spans a wide range of libraries, museums, and other repositories on the UC Berkeley campus.
The list below gives you an idea of the amount and diversity of non-fossil materials collected by the expedition and stored outside of the UCMP:
The Museum of Vertebrate Zoology has many mammal specimens that were collected during the UCAE by Thomas Larson, ranging in size from bats and elephant shrews to large antelopes.
The Phoebe A. Hearst Museum of Anthropology has large amounts of archaeological and ethnographic material, ranging from stone tools to stools, many of which come from the Ovambo people in South Africa. Faunal and archaeological materials collected at the Middle and Late Stone age excavation sites are also stored at Hearst.
The Music Library has a series of recordings of local traditional music from South Africa, recorded by famed ethnomusicologists Laura Boulton and Hugh Tracey.
The Bancroft Library holds many photographs documenting the life of Charles Camp and his family during the expedition. The library also has many photos of local people and their traditions, as well as the landscapes on which they lived.
The UC Botanical Gardens received seeds and living plants that were collected by Robert Rodin, and some of those living plants perpetuate and can still be visited in the African section of the garden.
The University and Jepson Herbaria also have a considerable number of specimens, as well as Robert Rodin’s field notes and correspondences. A complete list of everything collected can be found in his preserved field notes.
Fossil primates at the Evolutionary Studies Institute in Johannesburg, South Africa. Photo by Tesla Monson
Following our curatorial and historical work with this collection, we narrowed our focus to the Plio-Pleistocene fossil assemblage. For a more extensive historical account of the UCAE, and faunal and locality details for the Plio-Pleistocene fossil assemblage, see our recently published paper in PaleoBios (Monson TA et al. 2015).
As we turned our attention to the Plio-Pleistocene assemblage, two undergraduate students who were involved in the curatorial process took on independent projects. Sandy Gutierrez examined the ostrich eggshells and quantified interspecific variation in shell characteristics. And Bogart Marquez, emphasizing the bovids, studied the faunal composition of the different caves in order to make inferences about deposition, taphonomy, and predatory behavior in and around the caves. Both Sandy and Bogart presented their results at the Society for the Advancement of Chicanos and Native Americans in Science (SACNAS) conference in Spring 2014.
We also dug into the primate material with the goal of assessing the alpha-taxonomy of the UCMP specimens. This part of the assemblage includes specimens that have been very influential throughout the historical course of monkey taxonomy, and many are still quite controversial. We tag-teamed the project, with Marianne working through the mandibular material as part of her honors thesis and Tesla examining the cranial material. Two then-undergraduates in the Hlusko Lab also worked with the primate material: Kevin Roth examined the juvenile craniodental specimens and Sandy Gutierrez looked at the postcranial material.
Tesla poses for a selfie with Sediba, a South African australopithecine.
The whole group (Tesla, Marianne, Sandy, Bogart, and Kevin) presented our results during a UCMP Fossil Coffee seminar back in Spring 2014 and at the American Association of Physical Anthropologist (AAPA) meeting in April 2014. Fortuitously, our Fossil Coffee presentation was attended by Dominic Stratford, a visiting South African geoarchaeologist from University of the Witwatersrand in Johannesburg, South Africa. Dominic has become an invaluable collaborator on the multiple monkey projects that evolved out of our initial work in the UCMP and that are still ongoing. These projects led us (and our advisor – Leslea Hlusko) on the next leg of our journey. In summer of 2015, we journeyed to South Africa to collect more monkey data, a trip graciously funded by a grant from the Palaeontological Scientific Trust and two Desmond C. Clark fellowships from the Human Evolution Research Center at UC Berkeley.
The entrance to the hominid vault at the Evolutionary Studies Institute in Johannesburg, South Africa. Photo by Tesla Monson
During our time in South Africa, we studied monkey cranial and dental specimens at University of the Witwatersrand in Johannesburg and at the Ditsong Museum of Natural History in Pretoria. While it was an incredible experience and opportunity, we couldn’t help but feel like some of the days stretched on forever - we were in the museum for nine hours at a time, and some days it felt like all we had to eat was chicken, chicken, and more chicken.... which, according to Dominic, actually qualifies as a vegetable in South Africa. Tesla had to tape her thumbs, followed by her index fingers, followed by almost every other finger, to prevent caliper burn, and Marianne had to squint out of one eye for two weeks straight. (But we made sure to take semi-frequent jellybean breaks to preserve our sanity, thanks Leslea!) It may not have felt like it while we were squinting at calipers and working through the burn, but the amount of data collected made the long hours very worthwhile. Not to mention that we were in good company while at University of the Witwatersrand, since original South African hominid fossil material, including the Taung child, Malapa and Sediba, were displayed (complete with spotlights!) in the vault where we were working. Yes, that’s correct – a vault. We were stationed in the Hominid Vault at the Evolutionary Studies Institute, a very serious room fully equipped with a 6-foot vault door with rotating handle, locked by a 4-inch key that looked a hundred years old. Serious business indeed.
When we weren’t measuring and photographing monkeys, we got to take tours of some of the famous cave sites, and wow were they incredible! We also got to meet paleoanthropologist Ron Clarke and see the “Little Foot” hominid remains, which are still in the process of being prepared – an opportunity that has only been offered to only a handful of people in the world. Hey, it pays to be a paleontologist!
The surface layers at Sterkfontein Cave in the Cradle of Humankind, South Africa.
Marianne Brasil, Leslea Hlusko and Dominic Stratford underground in Sterkfontein Cave, South Africa. Photo by Tesla Monson
Marianne Brasil and Tesla Monson in Sterkfontein Cave. Photo by Leslea Hlusko.
Famed anthropologist Ron Clarke holding the cranium of “Littlefoot,” a recently discovered South African hominid.
In the evenings while we were in Pretoria, we ate our delivery dinners (mostly chicken) on the floor of Leslea’s room, and sometimes it was in candlelight because of this odd, but normal “it’s just a part of life here,” load-shedding phenomenon that causes small-scale city blackouts. This was only one of the quirks of South Africa that we encountered. Some others included…
No picture on a restaurant menu was ever actually replicated in person. Dishes served were a surprise every time!
The GPS had a fondness for telling us to “Turn left at unknown road”, as if that’s helpful.
On more than one occasion we had to let baby goats get out of the road before we could continue on our way. Ok, that last one wasn’t so bad… 🙂
Following all of the hard work of data collection, we finally got to explore South Africa. We set off - with Tesla driving on the wrong side of the road, in the wrong side of the car, and with the clutch on the left – to our rental at “Zonk Lake”, which was a lone cottage on a tiny lake. So, we basically rented a lake. It’s not often you get to take a romantic vacation with your labmate…
Giant’s Castle reserve in the Drakensberg. Photo by Tesla Monson
During the couple of days that we were in the Drakensberg region, we went out to enjoy the natural beauty of the landscape as well as the San petroglyphs of Giant’s Castle. We were also able to see our study organisms in their (not so) natural habitat when we ran into chacma baboons in a park area while out for a hike. On a more serious note, it was an honor and a privilege to tour the Apartheid Museum and the Nelson Mandela Memorial while we were in KwaZulu-Natal, and we highly recommend it to any visitors in the area.
San petroglyphs on the rocks at Giant’s Castle, South Africa. Photo by Tesla Monson
Chacma baboons (Papio hamadryas) eating grass at the Giant’s Castle resort in the Drakensberg. Photo by Tesla Monson
A panel from the Apartheid Museum at the Mandela Capture Site near Howick in KwaZulu-Natal. Photo by Tesla Monson
Taking the kayak out on Zonk Lake. Photo by Tesla Monson
Marianne practices the art of braai, South African barbeque. Photo by Tesla Monson
During the evenings, we caught Marianne up on the childhood media she never had, pulling from the random assortment of VHS cassettes that someone left on the shelf of our Zonk cabin: Casper, Mask of Zorro, Daredevil – all the greats. We also went kayaking in the early morning, and had true South African “braai” (AKA barbeque) in the evenings. You know what they say — when in South Africa...
After Zonk Lake, we left early for the nine-hour drive to Kruger National Park. Luckily, awesome street signs and plenty of bad jokes from Tesla dotted our journey. When we finally made it to Kruger, we quickly loaded up on snacks, brewed our coffee at 5:30 in the morning, and set out to drive through the park. The first thing we saw was a rhino (spotted by Tesla). We had heard that some people never see anything, so the mood was gleeful right way.
Then, maybe 20 meters down the road past the rhino, we saw an elephant (spotted by Marianne). The day just got better after that. We saw giraffes, lions, hippo, impala, hyena, kudu, crocodiles, warthogs, TONS of birds, baboons, buffalo, zebra, mongoose, and many other cool critters – including loads and loads of baby animals. Oh the babies!
A white rhinoceros (Ceratotherium simum) in Kruger National Park, South Africa. Photo by Tesla Monson
Southern ground hornbills (Bucorvus leadbeateri) in Kruger National Park, South Africa. Photo by Tesla Monson
Giraffes, impala and warthogs at a watering hole in Kruger National Park, South Africa.
An African elephant (Loxodonta africana) in Kruger National Park, South Africa. Photo by Tesla Monson
A baby spotted hyaena cub in Kruger National Park, South Africa. Photo by Tesla Monson
A zebra in Kruger National Park, South Africa. Photo by Tesla Monson
A warthog also known as “Radio Africa,” runs with its tail up. Photo by Tesla Monson
A vervet monkey hangs out near a rest area in Kruger Park, South Africa. Photo by Tesla Monson
Overall, our trip was really productive, and we had a really excellent time. We collected lots of data, generated many hypotheses we’re currently testing, and raised questions that we are working to answer. We will both be presenting at the AAPA meeting in April 2016 on some of our findings from the data collected on this trip. We also got to know each other really, really well and we’re both happy to say, we’d go on another data collection trip to Africa together anytime!
The sun sets over Kruger National Park, South Africa. Photo by Tesla Monson
Assistant Director Mark Goodwin and his project collaborators (see Feb. 1 blog post) made a surprising discovery while collecting microvertebrates, turtles, and fish. Within a small area of exposure in the Late Jurassic Agula Shale in the Tigray Province, just south of Mekele, Ethiopia, were the first sauropod dinosaurs ever reported from Ethiopia!
The team found mostly partial bones and bone fragments, and the local school kids delighted in holding Ethiopia's first sauropod dinosaur bones.
Mark labeling some of the bones with Conny Rasmussen (Univ. of Utah) and local school kids looking on.
Million Alameyeho & Samuel Getachew (Addis Ababa U.) and Tadesse Berhanu (Oklahoma State U,) with local school kids
Close up of some of the many sauropod bones found by the field party.
Tony and Liz by a billboard advertising the movie Demain, in Paris.
In December 2015 UCMP faculty curator Tony Barnosky and Stanford paleoecologist Liz Hadly attended The United Nations Conference on Climate Change to premiere a movie opening in Paris. The movie, Demain, was inspired by the 21-authored study that produced a 2012 Nature paper on tipping points. The film opens with Tony and Liz summarizing global change issues facing the world today.
Tony states, "the movie is all about solutions and is very uplifting." It features solutions being implemented in San Francisco and Oakland, in addition to many other places around the world. It was produced by and stars Mélanie Laurent, a well-known French actress, and Cyril Dion. The movie is getting rave reviews in Europe and the English version Tomorrow (see video) is anticipated to be released in the USA in the spring.
Tony and Liz (far left) with cast members of the film, Demain.
Research by Faculty Curator and Professor Tony Barnosky and the Anthropocene Working Group continues to support the strong need for designating a distinct geological epoch, the Anthropocene. Landscape-altering human activities leave behind distinctive evidence (plastics, aluminum, concrete, black carbon, among others) in the sedimentary record. The group has received widespread media attention and recent articles in the New York Times, Los Angeles Times, and Washington Post demonstrate the extent to which interested in topic crosses academic and non-academic boundaries.
On a related topic Tony is the co-author on a research article by Ceballos et al, 2015, on the sixth mass extinction, and it was the #3 most popular academic paper (and shared and read outside and within academia) published in 2015 according to Almetrics. It was also #15 in the top 100 Science papers listed in Discover Magazine.
Assistant director Mark Goodwin is in Ethiopia for several weeks as part of a collaborative project with UCMP alums Greg Wilson (University of Washington) and Randall Irmis (Utah). Together with colleagues from the University of Oklahoma, Addis Ababa University, and Mekelle University in Ethiopia, the team is investigating non-marine Mesozoic ecosystems from the Northwestern Plateau, Ethiopia.
Mark reports "we had great success in the Late Jurassic units and it is gratifying working with Ethiopian students and staff from the Earth Sciences Dept at Addis Ababa University. In the late Jurassic Mugher Mudstone, in addition to turtles, fish, croc teeth and verts, we found a partial crocodile skull with brain case and parietals, partial lower jaw, many allosauroid-like theropod teeth at almost every site and finally some large dinosaur bones - still fragmentary but we're getting there - and very rich micro vertebrate localities that just have to have mammals - collected some bags of sediment from each. Working with the Earth Sciences Dept at Addis Ababa University has been great and hopefully a model for future work and lots of opportunity for collaboration, including informal science."
This collaborative research project, "US-Ethiopia planning visit for the investigation of non-marine Mesozoic ecosystems from the Northwestern Plateau, Ethiopia," is funded by the National Science Foundation grant NSF-CNIC-1444238.
Group pic at the top of the flood basalts that cap the steep sided canyons of the Blue Nile Gorge, near Fiche, Ethiopia. From L to R: Tadesse Berhanu (PhD student, Oklahoma State); Conny Rasmussin (PhD student, Utah); Keegan Melstrom, PhD student, Utah); Randy Irmis (Utah); Greg Wilson (Washington); Mark Goodwin (UCMP); Dave Demar (Postdoc, Washington); Samuel Getachew and Million Mengesha (Earth Sciences Dept., Addis Ababa University).
The Fall 2015 issue of the Berkeley Science Review features an article by Sara ElShafie, a UCMP graduate student in the Padian Lab, on the McKittrick tar seep fossils that have been stored in the Campanile since the 1930s. The convergence of an Institute of Museum and Library Services grant to the UCMP to clean and catalogue more the 12,000 specimens in the collection and the centennial celebration of the Campanile in 2015 shined a spotlight on these unique fossils.
In interviews with UCMP graduate students Eric Holt and Ashley Poust, and UCMP staff Lisa White and Pat Holroyd, Sara details the work performed to preserve history and scientific significance of the McKittrick collection. Over 3,000 collective hours spent by more than a dozen students will improve the accessibility to the collection for future research and a rich digital archive facilitates sharing with the education community.
The Berkeley Science Review is a graduate student-run magazine showcasing research conducted UC Berkeley in a variety of disciplines.
At a Sierra foothills gold mine, White poses with Kirk Johnson, director of the Smithsonian National Museum of Natural History and narrator of “Making North America.” (Photo courtesy of Lisa White)
Making North America, a 3-part NOVA series that originally aired on PBS in November 2015, is a richly illustrated journey through the geological history of the North American continent. UCMP Director of Education and Outreach Lisa White appears in episodes one (Origins) and three (Human) in segments shot in northern California.
Lisa joins paleontologist and Director of the Smithsonian National Museum of Natural History Kirk Johnson, the series host and narrator, along the San Andreas fault in Tomales Bay and in a gold mine near Placerville, CA to explain the unique geological features in California.
Egyptian farmers in the Neolithic period 5,000-6,000 years ago.
Scientists have found an abrupt change about 6,000 years ago in how terrestrial plant and animal species coexisted, right about the time human populations were ballooning and agriculture was spreading around the world.
The findings suggest that human activity had reached a tipping point where hunting and farming were impacting the natural world in irreversible ways — changes that have continued to increase to this day.
The researchers, including UC Berkeley’s Cindy Looy, an assistant professor of integrative biology, will report their findings in the Dec. 17 issue of the journalNature.
The scientists looked at fossil data on how species coexisted over the past 307 million years, specifically how often a particular pair of plant or animal species is found within the same community. Out of all possible combinations of two species in a certain region and time interval, the proportion of pairs of species that co-occurred remained relatively stable until 6,000 years ago. At that time, the chances of co-occurrence dropped significantly, suggesting that humans were creating some barrier to the dispersal of plants or animals.
"This tells us that humans have been having a massive effect on the environment for a very long time," said lead author S. Kathleen Lyons, a paleobiologist in the Evolution of Terrestrial Ecosystems (ETE) program at the Smithsonian Institution's National Museum of Natural History in Washington, D.C.
Analyses of modern communities of plants and animals have found that for most pairs of species, the presence of one species within a community does not influence whether the other is present or absent. For pairs where there is an association, most occur within the same community less frequently than expected, suggesting some influence keeps them apart.
But when Lyons, Looy and their colleagues investigated the composition of ancient communities using fossil data, they found exactly the opposite. Their analysis showed that from 307 million years ago, the time known as the Carboniferous period, to about 6,000 years ago, in the Holocene epoch, there was a pattern of pairs of species occurring together within communities rather than being segregated.
"The proportion of co-occurring species pairs was relatively stable from the late Paleozoic until 6,000 years ago, even during periods of major climate change and mass extinction and despite the appearance of many new players in the terrestrial ecosystems, such as mammals and flowering plants," Looy said. "The decline of coupled species pairs in the Holocene also cannot be explained by the transition from the last glacial to the current interglacial at the end of the Pleistocene, as this happened too early. Instead, it is more likely caused by an increase in human population size and the resulting land use and agriculture."
Around the time co-occurrence patterns changed, humans were becoming increasingly dependent on agriculture, a cultural shift that physically altered the environment and would have introduced artificial barriers to dispersal never seen before. Even at low levels of agriculture and other human impacts, there was a detectable shift in co-occurrence structure, indicating that species were not able to migrate as easily as they did for the previous 300 million years.
For more details about the study, see this story on the Smithsonian's website.