Field Museum Scientists Featured in Evolving Planet

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Robert D. Martin, PhD
Anthropology Department
Curator, Biological Anthropology and
Provost, Academic Affairs

CHICAGO - March, 2006 - Biological anthropologist Bob Martin has devoted his entire career to exploring the evolutionary tree of primates. In addition to our own species Homo sapiens, the order Primates contains about 350 other living species, ranging from lemurs to monkeys to apes. In addition, there are almost 500 fossil species dating back as far as 55 million years ago. In his quest to achieve a reliable reconstruction of primate evolutionary history, Martin has studied an extensive array of characteristics in the living species, including anatomical features, physiology, chromosomes and DNA.

Martin has been particularly interested in the brain and reproductive biology, as these systems have been of special importance in primate evolution. With skeletal features, it is possible to include the fossil evidence and thus to include geological time in the picture. By studying living primates in the field in the forests of Africa, Madagascar, Brazil and Panama, Martin has also been able to include behavior and ecology in an overall synthesis. That synthesis was first presented in his textbook Primate Origins and Evolution, published by Princeton University Press in 1990. Since then, Martin has been working on various refinements.

“A proper understanding of primate evolution provides an essential basis for interpreting the special case of human evolution,” Martin says. “Without this secure foundation, it is exceedingly difficult to produce convincing explanations for the evolution of all of our special features. If we restrict ourselves to comparisons of humans and our closest relatives, the great apes, we are continually forced to draw conclusions that have no generality and are not testable.

“One good illustration of the need for broad comparisons is provided by investigations of the timescale for primate evolution,” Martin continues. “Although the earliest known primate fossils are only 55 million years old, our statistical analysis allowing for gaps in the fossil record indicates that primates actually diverged from other mammals about 90 million years ago. When this result is applied to the specific case of human evolution higher up in the tree, it emerges that our lineage probably branched away at least 8 million years ago, earlier than previously thought.”

Lance Grande, PhD
Geology Department
Curator, Fossil Fishes and
Vice President for Collections and Research

Lance Grande is crossed trained as a biologist and a geologist. He studies the comparative osteology (structure and function of bones), ontogeny (developmental history) and biogeography (geographic distribution through time) of fossil and living fishes. His work has with a particular emphasis on the ray-finned fishes Actinopterygii, a group containing half of all known vertebrate animals. Grande is also interested in the philosophy and application of methods used to interpret evolution and earth history. Some of the fish groups Grande has done major studies on include the Siluriformes (catfishes), Clupemorpha (herring and herring-like fishes), Osteoglossomorpha (bony-tongues) and other more primitive actinopterygian groups such as sturgeons, paddlefishes, amiiforms, gars and bichirs.

Grande is also especially interested in the origin and evolution of the modern North American freshwater fishes as well as in developing new techniques for preparing fish fossils so their skeletons can be better exposed for detailed comparisons with living fishes. Every year he conducts fieldwork in the famous Green River formation in southwestern Wyoming, where he works in some of the world’s most productive fossil beds. This uniquely rich fossil bonanza includes a beautifully preserved, extinct, 52-million-year-old tropical lake community containing millions of beautifully preserved fossil organisms, from microscopic bacteria and insects to 13-foot-long crocodiles and palm trees.

“It is an honor to oversee the largest, most diverse fossil fish collection in North America, containing more than 30,000 specimens from single fish skeletons to large slabs of rock with more than two hundred individual fish,” Grande says. “As a biologist, I also work with living fishes. In addition to our huge fossil fish collection in the Geology Department, The Field Museum has the good fortune of having over 2 million recent fishes in the Zoology Department, and of being located near the Shedd Aquarium, with all its wonderful resources. There is no better place in the world to study the evolution and biodiversity of fishes than The Field Museum.”

Olivier Rieppel, PhD
Geology Department
Curator, Fossil Amphibians and Reptiles

During the Mesozoic, also called the “Age of Reptiles,” a number of reptile lineages secondarily adapted to a life in the sea. Over the last few years, Olivier Rieppel pursued the global revision of Triassic stem-group Sauropterygia, marine reptiles that later gave rise to the more widely known plesiosaurs, pliosaurs and elasmosaurs of the Jurassic and Cretaceous. This work provided the basis for the ongoing collaborative research program with faculty and students of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, focusing on new collections of Triassic marine reptiles from Guizhou Province in southern China. These new collections require taxonomic work not only on sauropteryians, but on other marine reptiles such as thalattosaurs and protorosaurs as well. The Triassic record of marine reptiles is rich and diverse, and allows the study of broad evolutionary patterns as originally terrestrial lineages adapted to marine habitats.

More recently, Rieppel has become involved with research on the origin of snakes, a program that will continue. Again of a collaborative nature, this research seeks to integrate paleontology, comparative morphology and molecular systematics. The origin of snakes is a longstanding problem in the evolution of reptiles that still awaits a satisfactory resolution. The study of the origin of snakes is now embedded in a broad-scale investigation of the phylogenetic relationships of squamate reptiles as part of the Tree of Life program sponsored by the National Science Foundation.

“Researching the evolution of various reptile lineages and reconstructing their phylogenetic past raises a number of theoretical and methodological issues that require philosophical analysis,” Rieppel says. “I take an active interest in the history and philosophy of comparative biology.”

Meenakshi Wadhwa, PhD
Geology Department
Curator, Meteorites

Meteorites are rocks that have fallen to the surface of the Earth from interplanetary space. They are in essence “space probes” that make it possible for us to explore other worlds without physically having to go there. While most meteorites originated from asteroids, a few are thought to have been ejected by large impacts on the surfaces of the Moon and Mars. Meenakshi Wadhwa studies the chemistry of these “rocks from space” to understand how and when our solar system and the planets within it were formed.

To do this work, she has established a state-of-the-art geochemistry and geochronology laboratory at The Field Museum. Wadhwa is a team member of Genesis, the NASA spacecraft mission that brought back samples of solar wind (streams of particles flowing outwards from the Sun). She will be studying these samples in her laboratory to understand the chemical composition of the Sun, which makes up more than 99% of the mass of our solar system. She is also involved in future NASA missions to send rovers to the surface of Mars that will help us to understand the history of water on that planet and whether life ever evolved there.

“What most people don't realize is that much of what we know about our beginnings, the origin of the solar system and of the Earth, and the very atoms that make up everything around us, comes from studying meteorites,” Wadhwa says. “Meteorites and other samples brought back from spacecraft truly offer us a unique opportunity to understand the inner workings of the physical universe around us.”

John R. Bolt, PhD
Geology Department
Curator, Fossil Amphibians and Reptiles

The origin and early evolution of tetrapods is one of the main research interests of vertebrate paleontologist John Bolt. Tetrapods are four-limbed vertebrates, a category that includes humans. The earliest known tetrapods are from the Late Devonian, about 380 million years ago. Devonian tetrapods are found in fewer than a dozen localities, worldwide. Tetrapod localities from the Mississippian, 359 to 318 million years ago, are also rare, with only about two dozen localities worldwide. Bolt is currently studying Mississippian tetrapods that he collected from a locality in southeastern Iowa. These specimens, plus those from a locality in West Virginia and another one in southern Illinois, represent all of the most productive Mississippian localities in the United States.

Preservation of many of these U. S. Mississippian specimens is very good, and in some cases exceptional. Preservation quality is particularly important in the case of the earliest tetrapods. These specimens have turned out to show many unexpected features, which would have been difficult to interpret from poorly preserved material. Taken together, the increasing numbers of specimens from the Devonian and Mississippian are finally beginning to give scientists a look at the first tetrapods.

“The earliest tetrapods would have been expected to be primitive, and this has turned out to be the case,” Bolt says. “Nevertheless, something that has impressed me most about Mississippian and Devonian tetrapods is just how primitive they were. Rather than looking at them as just very primitive tetrapods, it is often helpful to think of them as highly evolved sarcopterygian fish. But whether you view them from a fish perspective or a tetrapod perspective, one of the best things about studying early tetrapods is the way it forces you to change your expectations.”

Peter Makovicky, PhD
Geology Department
Curator, Fossil Amphibians and Reptiles

Peter Makovicky studies the evolutionary history of dinosaurs. His research is particularly focused on small theropods (carnivorous dinosaurs) and how they evolved into living birds. The theropods closely related to birds had wing feathers, brooded their nests, and were small animals that were virtually indistinguishable from the earliest bird Archaeopteryx in all but a few features. Makovicky also focuses on the horned dinosaur group Ceratopsia, which includes animals such as Triceratops and Protoceratops.

Makovicky has conducted fieldwork in Wyoming, China, India and Argentina, and he has described six new dinosaur species with colleagues from various parts of the world. He considers dinosaurs to be a poster child of evolutionary research.

“In 1995 we had a strong evidence that birds evolved from small, dromaeosaurid-like dinosaurs,” Makovicky says. “Nevertheless, there was still a gap between the anatomy of birds and non-avian theropod. There was also and much debate regarding how many of the traits that characterize birds, such as feathers, flight ability, and nest care, may have evolved. In the intervening decade, new theropod discoveries from around the world have provided amazing answers to many of these questions.”

Scott Lidgard, PhD
Geology Department
Associate Curator, Fossil Invertebrates

Scott Lidgard is a paleoecologist currently studying the role of biological forces such as predation as a possible driver of large-scale trends in the history of life. His work focuses on cheilostome bryozoans, which are marine invertebrates that live on the bottom of the sea in colonies of two to two million individuals and take on an enormous variety of shapes. The complexity, colonial nature, and excellent fossil record of bryozoans make them ideal subjects for studying general patterns of ecology and evolution.

Lidgard uses ecological, morphological, and fossil diversity patterns of bryozoans to try to test operational explanations of trends driven by predation. He looks at the precise timing and co-occurrences of predators and prey in the fossil record; the appearance and spread of skeletal armament among fossil bryozoans; and the mechanisms of attack and dietary specialization of bryozoan consumers alive today. By combining these different perspectives he uses the extent to which evidence from a great number of cases independently validate or dispute hypotheses of biological trends driven by predation.

“One of the commonest fates of all organisms is to be eaten alive, in whole or in part,” Lidgard says. “We know from countless field studies and experiments that predation is an important force molding the bodies and life histories of organisms. There is also a wealth of evidence that predation is one factor structuring the distribution and abundance of organisms, and for some species causing extinction in ecological time. Yet how predation correlates with large-scale trends in the diversity and forms of organisms over millions of years on a global scale continues to be debated.”

Jennifer McElwain, PhD
Geology Department
Associate Curator, Paleobotany

Jennifer McElwain is interested in the interactions between plant biodiversity and climate change in the geological past. Specifically, she studies how changes in greenhouse gasses, such as carbon dioxide, can directly and indirectly (via greenhouse-induced global climate change) influence the relative abundances and diversity of different plants. She studies three important intervals in Earth history: the Triassic-Jurassic boundary (about 200 million year ago); the Early Toarcian (about 178 million year ago); and the Cenomanian-Turonian boundary (about 90 million years ago). Each of these intervals is characterized by major extinction events among marine invertebrate organisms.

Studying past biodiversity using the fossil record is extremely difficult. Only a minute proportion of the Earth’s original biodiversity at any one interval in the past is preserved as fossils. Scientists also have to contend with the fact that the fossil record of animals and plants is full of bias towards organisms that have a high preservation and fossilization potential, such as hard rather than soft-bodied organisms or, in the case of plants, abundant long-lived woody plants rather than rare annual herbs.

“The fossil record can provide an excellent means with which to study changes in the relative diversity and relative abundance of different plant and animal groups through time,” McElwain says. “Such analyses enable us to track the ecological dominance of different plant groups through time and assess how climatic changes and changes in atmospheric composition affected these patterns.”

Peter Wagner, PhD
Geology Department
Associate Curator, Fossil Invertebrates

Snails (gastropods) are one of the most successful and diverse animal groups. Because of their hard shells, they have left a dense fossil record from the late Cambrian (about 500 million years ago) to the present. Paleontologist Peter Wagner studies shells of gastropods and related mollusks from the Cambrian through the Devonian (about 350 million years ago) in order to test ideas about what caused different long-term evolutionary patterns. For example, he studies the long-term diversification and/or elimination of some shell types, how rapidly new shell forms and/or new species appear, and who survives and dies over mass extinction events.

Wagner’s studies have shown that snail shells changed more frequently and more drastically early in gastropod history. They also have demonstrated that particular types of shells evolved far more frequently than expected given the range of possible shell types. In addition, they have shown that many now extinct shell types once were not only common but also evolving frequently. Wagner’s research is funded by the National Science Foundation and has included fieldwork in the Australian outback as well as visits to other museums across the globe.

“A wide range of hypotheses, ranging from issues as big as ‘what caused the explosion of different animal types during the Cambrian?’ to as basic as ‘how do animals evolve into distinctly different species?’ all make testable predictions about the gastropod fossil record,” Wagner says. “In many cases, gastropods are much better for testing basic hypotheses than are the animals or plants who originally inspired the hypotheses, because we know much more about snails as animals and because gastropods have such a denser fossil record than other species do. My work involves combining the data that I collect with computer programs I write in order to separate the hypotheses that might work from those that clearly do not.”