Freshly dug plant fossils at Laguna del Hunco.Credit Peter Wilf
New clues to extinction
In 2000, Wilf decided to bring quantitative techniques to bear on a classic paleontological problem—the asteroid strike that occurred 65 million years ago at what geologists call the K-T boundary. This massive impact and its subsequent atmospheric effects are now widely believed to have caused the extinction of the dinosaurs.
Wilf first encountered the K-T boundary via the studies of Kirk Johnson of the Denver Museum of Nature & Science, who had demonstrated that a massive plant extinction occurred at the same time as that of the dinosaurs. Starting in the late 1980s, Johnson collected over 22,000 specimens to document his findings, and in 2002, Wilf, Labandeira, and Johnson graded most of them for insect damage. This work provided the first conclusive evidence of a wide-scale insect extinction at the same time.
Wilf, Johnson, and colleague Brian Huber next used paleoclimatic analysis techniques on the entire collection. Their study documented a brief warming period 200,000 to 300,000 years before the asteroid hit, followed by a cooling about 100,000 years later, both correlating to the marine fossil record of that time. But this temperature spike had little influence on plant or animal species diversity, they concluded.
A further analysis of the floral turnover across the K-T boundary itself, however, added significant knowledge to what was known about the plant extinction at the time of the asteroid impact. It revealed the dramatic and immediate loss of at least 60 percent of plant species and a comparable number of the insects that ate them. "These effects are long-lasting, through the Paleocene era," Wilf says.
In Patagonia
In 1997, Wilf recounts, Kirk Johnson made a trip to Argentina's Patagonia region, and while there briefly visited a site that was something of a legend to paleobotanists: the ancient crater lake named Laguna del Hunco. Fossil plants were first discovered there in the 1920s, but the number of specimens taken had been small, and they had been somewhat unscientifically collected. The site, located seven hours by land from the nearest city, had been visited only sporadically since then. Given only 45 minutes to canvas the area by his Argentinian guide, Johnson spent the time photographing specimen after specimen of beautifully preserved fossils.
After seeing Johnson's photos, Wilf immediately began writing research grants to study the area. An award from the National Geographic Society enabled him to begin work at the site in 2002. In 2004, he was awarded $500,000 through the NSF Biodiversity Surveys program, and in the year following he received both the John T. Ryan, Jr., Faculty Fellowship from the Penn State College of Earth and Mineral Sciences and a $625,000 Packard Fellowship, a "bolt from the blue" award that gives him great latitude in how the money can be used. On several ensuing visits to Patagonia, Wilf and his collaborators have begun to excavate, thoroughly collect, and canvas for the first time what he calls "one of the most diverse fossil floras ever, from any time period, anywhere."
"Laguna del Hunco is an amazing white and black landscape," Wilf explains. "It's a white lakebed full of fossils—and black volcanic rocks. A huge eruption, probably in the early Eocene, created a caldera, which sagged afterwards, forming a lake. The animals and plants then were deposited in this small lake in the side of the caldera."
At this remote site, and at two others nearby—Río Pichileufú and the Salamanca Formation—exists a previously unknown diversity of ancient plant life dating from the Paleocene and Eocene epochs. "It's just completely outrageous," Wilf says, "because you're walking along and you see fossils on the ground everywhere—fish and frogs and insects too. I've seen two of my colleagues literally break down into tears there because they couldn't handle it."
Already Wilf's team has identified over 186 new species. "We have more than enough specimens right now," he says, "to write high-profile papers in very high-quality journals for a long time without ever having to collect another fossil. Everything about it is important, because the deep-time history of South America is very poorly studied, compared with that of Europe or North America."
"Particularly in terms of South American insects and insect damage, there's never been anything close to what we're studying at Laguna del Hunco. South America today has one of the most, if not the most diverse insect faunas in the whole world—but for the last 65 million years, the entire paleontological insect record consists of about 80 species. The entire insect damage record consists of one or two illustrations. Everything we're doing there is new."
"That region is very different from the rest of the world, geographically and botanically," he adds. Though today Patagonia is arid, shielded from Pacific moisture by the Andes mountains, at the time these specimens were deposited, 62 to 47 million years ago, the region was still connected to Gondwana, a massive southerly supercontinent that included parts of present-day Antarctica, Australia, and South Africa. The Andes didn't arise for many millions of years, Wilf notes, so the region was probably sub-tropical and wet.
The discoveries at Laguna del Hunco indicate conclusively and for the first time that South America has a long history of high plant diversity. But because of the poor fossil record, evolutionary connections to the plants of modern South America have been elusive. "We're actually having trouble finding a really good example of something that's alive today in the South American tropics that resembles what we're finding," Wilf says. "We're discovering instead that the flora at Laguna del Hunco is more closely related to what's now in northeastern Australia, New Caledonia, and other areas of the southwest tropical Pacific"—regions once part of Gondwana. Patagonia is part of this big ancient ecosystem, but until now there hasn't been a really effective large-scale effort to find out what these plants are, how old they are, how many there are, and what ate them."
The team is currently working on identifying its massive finds. "We have people working on the fish, the frogs, the plants, the insects, and the insect damage on leaves," says Wilf. Specimens from the 25 principal quarries at Laguna del Hunco are trucked to the Egidio Feruglio Paleontological Museum in Trelew, on Argentina's east coast. There, paleontologist Rubén Cúneo, co-principal investigator on the project, and other project participants analyze, photograph, and store the specimens. But the roads become impassible during the frigid Argentinian winter, which prevents work in the field during North American summers.
Wilf and his colleagues also face a severe lack of contextual history, partly because collecting fossils in the tropics, where the groundcover is so dense and topsoils are so thick, is notoriously difficult. "There are huge gaps to fill," he admits. But we can say that South America in general had a lot of diversity, and we can document that diversity back at least 55 million years."
Researchers in the field at Laguna del Hunco, Patagonia, Argentina.Credit Peter Wilf
At home with fossils
The summer of 2006 found Wilf characteristically busy, attending research conferences in Bilbao, Spain and Beijing. This November he'll be back in Patagonia, collecting plant fossils from the late Cretaceous era. Another ongoing project involves correlating the numerous leaf characteristics he and others have identified with the "phylogeny of angiosperms,"—that is, the evolutionary tree of flowering plants.
But it may be here in the Smithsonian's storage rooms that he is most at home. As we walk through the narrow passageways, Scott Wing hails him in friendly tones, and a couple of graduate students seem eager to see him as he stops to check on their work. Then, over the course of a long summer afternoon, he briskly tours me from case to case, room to room, revealing the museum's hidden treasures: spiral-shaped arthropod fossils the size of manhole covers; fossil boles of ancient conifers that once stood in present-day Maryland; inked mylar drawings, created from field sketches, of plant-insect interactions from Laguna del Hunco; and thousands of red-tinted glass slides containing one of the best existing collections of "cleared leaf" specimens—modern leaves that have been bleached and stained to make their vein patterns more visible.
My time is almost up, but the indefatigable Wilf beckons me to yet another row of towering archival cabinets, eager to show me one more fossil collection to which he has contributed. As I protest gently, citing the rush-hour traffic that awaits outside the museum, he pauses and smiles indulgently.
"Why," he asks at last, "would you ever want to leave this place?"
Peter D. Wilf, Ph.D., is assistant professor and John T. Ryan, Jr. Faculty Fellow of geosciences in the College of Earth and Mineral Sciences; pdw3@psu.edu. Some of the work described above was funded by the National Science Foundation. In addition, in 2005 Wilf was awarded a Packard Fellowship for Science and Engineering from the David and Lucile Packard Foundation. Data from the Laguna del Hunco project will eventually be made public through the NSF-funded Paleobiology Database and a bilingual Penn State-hosted website.
