PROFILE PROFILE Profile of David Jablonski Nicholette Zeliadt Science Writer Human activities are creating major environ- Batten, Norman Newell, and Niles Eldredge mental changes on the planet, contributing taught Jablonski to look at fossils as objects to habitat loss, climate change, pollution, of serious scientific study and allowed him and consumption of natural resources. Such to sit in on their lively graduate seminars. changes place enormous pressures on biodi- “That’s when I began to get a much better versity, disrupting long-standing evolutionary sense of paleontology as a profession and as processes. David Jablonski, a paleontologist a science,” he says. at the University of Chicago and a recently Then, in 1973, Jablonski says he had an elected member of the National Academy epiphany after reading the book Evolutionary of Sciences, integrates studies of past orig- Paleoecology of the Marine Biosphere,by inations and extinctions of species and James W. Valentine (1), realizing that he higher taxa with data on the distributions could potentially use the marine fossil record and evolutionary relationships of living spe- to answer some of the big, open questions in cies to provide a multidimensional picture the fields of evolution and ecology, such as of how biodiversity has worked over geo- the environmental factors that govern the logical timescales. Jablonski’s research has emergence of new species and the impacts of focused primarily on the extraordinarily mass extinctions on evolutionary patterns. abundant and well-preserved fossils of ma- “This book changed my life. It was so am- David Jablonski in one of his favorite field rine bivalves, such as scallops, cockles, oys- bitious and so creative that I realized that areas, the Smithsonian collections. Image ters, and mussels, and has helped to reveal this was what I wanted to do,” Jablonski says. courtesy of Susan M. Kidwell. how these organisms and their spatial distri- Also, thanks to Valentine’s book, Jablonski butions have evolved over space and time. decided that he wanted to be both a biologist fi “ biology and ecology, and they were very His ndings could shed light on the origins and a geologist. I even conned the Dean of fi of global variations in diversity, how evolu- Students at Columbia into letting me do a stubbornly ne-scale; the way that you tionary lineages collapse or rebound from double major in biology and geology, which studied evolution or ecology was that you mass extinctions, and how evolutionary pro- was relatively unusual at the time,” he recalls. simply extrapolated from the year or two yearsorthreeyearsofastudytomillions cesses might operate at several levels at once. of years,” Jablonski says. “I wanted to know These findings may even provide lessons for Paleobiological Revolution if you really could do that.” He began think- the future preservation of biodiversity. During this time, Jablonski witnessed a revo- lution in the field of paleobiology as it moved ing about how he could convert largely the- Nights at the Museum away from an emphasis on using fossils for oretical and somewhat abstract ideas into Bythetimehewasfive years old, Jablonski environmental information and relative age- hypotheses that could be tested with data knew he wanted to be a paleontologist. determination, and as confirmatory support from the geological record. Born in New York City, Jablonski grew for existing evolutionary ideas. The field was As Jablonski neared the completion of his up near the American Museum of Natural morphing into a theoretical discipline that undergraduate degree, Rhodes Fairbridge, a History, his self-described “home away from expanded the range of evolutionary mecha- geology professor at Columbia University, home,” where he became fascinated with nisms that operated over long timescales (2), recruited him to coedit The Encyclopedia of the museum’s dinosaur fossils from a very beginning with Stephen Jay Gould’sand Paleontology. By the time Jablonski started early age. His parents, both writers, encour- Niles Eldredge’s landmark argument for graduate school at Yale University in the aged what Jablonski calls an “intellectually punctuated equilibrium (3), which held that mid-1970s, he had contacted more than freewheeling existence,” and gave him the species are relatively stable over long time 100 prominent paleontologists and had freedom to follow his passion. intervals and show “punctuated” evolution- begun editing their contributed articles. As an undergraduate at Columbia Uni- ary changes concentrated in sudden, isolated More importantly, Jablonski had established versity in the early 1970s, Jablonski made episodes. working relationships with some of the fi ’ regular visits to the museum, but did so in a Jablonski found the punctuated equilib- eld s heavyweights, including James Val- city-wide work-study program called the rium model particularly fascinating, because entine, Thomas Schopf, Steven Stanley, and “ Urban Corps. “It was one of the great thrills he had already been pondering the problem David Raup. I had a reason to walk up to of my life,” Jablonski says. “One day I was of how to extrapolate from short-term con- them at meetings, which is sort of hard to wandering the halls of the museum and the tinuous, gradual changes in observable pop- next day I was behind the scenes working ulations to the long-term, large-scale shifts fi ” “ This is a Pro le of a recently elected member of the National for people there. At the museum, the promi- seen in the geologic record. As an under- Academy of Sciences to accompany the member’s Inaugural Article nent invertebrate paleontologists Roger graduate, I’d taken courses in evolutionary on page 10487. www.pnas.org/cgi/doi/10.1073/pnas.1309893110 PNAS | June 25, 2013 | vol. 110 | no. 26 | 10467–10469 Downloaded by guest on September 27, 2021 do when you’re a starting graduate student,” stages of these shells, and those can be work at the University of California at Jablonski says. very difficult to identify,” Jablonski recalls. Berkeley, where he immersed himself in Jablonski’s graduate research grew out Jablonski soon set off on a fossil-collecting evolutionary biology and, while keeping of his undergraduate work on fossilized spree from New Jersey to Texas, and also an interest in the present-day mollusks, shells from the Late Cretaceous Period, examined collections of Late Cretaceous fos- began to think in detail about the diversity roughly 65–80 million years ago, shortly sils housed in various museums, keeping dynamics he saw in the Late Cretaceous before the mass extinction that wiped out detailed notes and drawings of each specimen fossil record of the Gulf and Atlantic coasts. the dinosaurs. “Thanks to Norman Newell, on a series of index cards, one for each spe- However, Jablonski wasn’t the only one I worked up some fossil samples from some cies in the region. He analyzed the many studying fossils from this region: David Late Cretaceous localities that were just hundreds of species recorded in a period of Bottjer, a paleontologist at the University amazingly well preserved,” Jablonski re- nearly 16 million years of the Cretaceous of Southern California at Los Angeles, was calls. “It was as if you picked them up off a Period, and some interesting patterns began also working there on rocks of the same beach today.” Thebeautyofthefossils to emerge. “I found that I could see rules of age. Jablonski focused mainly on species captured his imagination and opened doors extinction and survival according to life that had lived near the shoreline, whereas for new directions of study. habits and geographic range sizes. I could Bottjer focused on those from environments even predict the species durations based further off-shore. When the two compared A Rocky Start on the mode of development, which I got notes, it became clear that the off-shore Jablonski knew that if he wanted to work on from the fossil larval shells,” Jablonski says. communities looked relatively archaic and Late Cretaceous fossils, he would need to gain This work also allowed him to directly test the on-shore communities looked relatively experience in the rocks of that age, so he the idea that species could act as units of modern. “There was this weird temporal went to Yale to work with Karl Waage, a selection, a controversial extension of the disconnect in the Late Cretaceous,” Jablonski paleontologist who specialized in that time punctuated equilibrium idea. Starting with says. Their friend Jack Sepkoski, then at the interval. While at Yale, Jablonski inter- the premise that geographic range is a species- University of Chicago, was finding similar acted with Rudolf Scheltema at the Woods level property and not one of individual onshore-offshore contrasts in Paleozoic Hole Oceanographic Institution in Massa- organisms, Jablonski showed that the classic ecosystems, and this prompted the trio to chusetts, who had recently written a paper Darwinian criteria for natural selection ap- write a synthesis paper describing nearly about larval ecology and evolutionary rates plied to his Late Cretaceous mollusks at the 500 million years of ecological history (9). in snails (4). Scheltema held that methods species level. Specifically, he found that the After several years documenting that the for inferring modes of larval development species varied in their geographic range size, observed pattern was genuine and bio- in living species could be applied to fossil that their survival or duration in the geologic logical and not an artifact of preservation shells if they were sufficiently well-preserved. or sampling, it became clear that the on- “ ” “ record varied with geographic range, and that That was fantastic, Jablonski recalls. Here this variation in geographic range was “heri- shore-offshore ecological pattern was pro- was a way of looking at the life history table”: that is, closely related species were duced by a tendency for major groups, such strategies of species that were extinct for 75 as sand dollars and stony corals, to origi- ” more similar in range size than expected by million years.