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Smithsonian National Museum of Natural History

Department of Paleobiology

Dr. Labandeira working

Conrad Labandeira working in the Karoo Basin.

Dr. Conrad Labandeira

Dr. Conrad Labandeira

Conrad Labandeira was born and raised in the San Joaquin Valley of central California. While helping his family tend the crops on their 30-acre farm, Labandeira’s interest in insects and their effects on plants was founded.

Labandeira attended undergraduate school at California State University, Fresno, where he received a bachelor's degree in 1980 as a triple major in biology, geology and anthropology. He received his Masters degree from the University of Wisconsin, Milwaukee, and went on to receive his Ph.D. from the University of Chicago. His dissertation focused on a morphologic (phenetic) classification of recent insect mouthparts, and the application of this classification to the phylogeny of insects in order to determine the history of insect dietary guilds and functional feeding-groups.

Labandeira joined the Department of Paleobiology at the National Museum of Natural History in 1992. His research has focused primarily on plant-insect associations in the fossil record, insect paleoecology and the evolution of terrestrial ecosystems. He actively researches sites in Colorado, Wyoming, Montana, North Dakota, Kansas, Nebraska, Québec, Argentina and South Africa.

For more information about his research, see his curriculum vitae...

Tales of Extinction and Recovery

How can scientists be sure of their evidence for the mass extinctions occurring at the end of the Permian Period about 251 million years ago?

A new paper by Conrad Labandeira and colleagues (Gastaldo, R.A., R. Adendorff, M. Bamford, C.C. Labandeira, J. Neveling and H. Sims. 2005. Taphonomic trends of macrofloral assemblages across the Permian-Triassic boundary, Karoo Basin, South Africa. Palaios 20: 480-498) examines plant fossils in South Africa’s Karoo Basin at the critical Permian/Triassic Boundary.  The paper provides cautionary evidence addressing previous claims that a regional extinction of land plants resulted in a definite change in the patterns of rivers and streams in the Karoo Basin. The paper questions these earlier conclusions, and raises additional questions regarding the timing of terrestrial extinctions in this area.

The Karoo Basin covers nearly two-thirds of South Africa and provides an unmatched record of evolving paleoenvironments during which changes in biodiversity occurred.  Scientists study the fossil record of this basin because it represents globally the most complete terrestrial Permian-Jurassic sequence for a land-based deposit.  Although similar marine geological successions are present in India, China, and Russia, they are not as complete as the Karoo Basin, one of the few basins worldwide in which the terrestrial fossil record for the 45-million-year interval spanning the Permian/Triassic (P/Tr) Boundary is preserved and exposed. Labandeira has evaluated plant-insect associations from recent but also extensive and earlier field collections that are housed at the University of the Witswatersrand in Johannesburg for Permian material, and at the South African National Biodiversity Institute in Pretoria for Triassic material.

The Karoo Basin provides an ideal site for scientists to collect fossils illuminating the Permian/Triassic Boundary (P/Tr) that was marked by the greatest mass extinction during the last 600 million years of Earth history, an extinction when perhaps 96% of species disappeared. Nearly 90% of marine species and 65% of reptile species went extinct and insects also suffered their greatest mass extinction in Earth’s history. Because understanding the mass extinctions of the P/Tr Boundary is so critical, and because “it is possible that the extinction event may have varied regionally in magnitude and timing, and the effects on land may pre-date, be coincident with, or post-date the effects documented in the oceans,” the authors of the Palaios article maintain that it “is essential that high quality, comparable data sets be acquired and evaluated to understand continental biodiversity loss at this critical time.”

The recently published paper evaluates fourteen stratigraphic sections (some previously published, some newly discovered) in order to describe the change through time of the taphonomic filters that controlled each of the fossil assemblages under review. Taphonomy refers to the effects of the environment on the preservation through time of the fossil record.  This paper concludes that a change in plant taphonomic character occurred within the Karoo Basin at this critical time period, and is related to changing fluvial (river) regimes and a climate controlled landscape.  In other words, the changing landscape through time had a definite preservational effect on which plant assemblages became fossilized, and hence conclusions about extinction based on surviving assemblages have to be made carefully. As the paper concludes, “the presence of plant fossils in the Early Triassic…indicates that the landscape was stabilized by a variety of vegetational architectures, providing evidence to negate previous claims that a regional extinction/extirpation of plants resulted in a change in fluvial style in the Karoo basin.”

The authors further conclude that “without a full understanding of the processes responsible for the generation and preservation of the data … used to interpret the response of the terrestrial ecosystem to the P/Tr boundary event, care should be taken in its application.”  As the authors state regretfully, “this conclusion is less desirable than one where the study’s results could address directly the questions and hypotheses on the response of vegetation to the P/Tr boundary event… But, the results presented here record the outcome of the physical, chemical, and biological processes that operated within the Karoo basin during, and subsequent to, the Late Permian.”  The authors ironically end their article with a final thought: “A more complete record is desirable, but compromised by nature itself.” In other words, taphonomy rather than extinction may explain which plant fossils came down to us through time.

Major geological strata of the Karoo Basin.
Major geological strata of the Karoo Basin.

Mass Extinction: The P/T Boundary

timelineThe earlier Permian Period of the Paleozoic Era occurred 299-252 million years ago. The Triassic Period of the Mesozoic Era occurred 251-200 million years ago.

The end of the Permian (P/T) was marked by the greatest mass extinction of the last 600 million years of Earth history, during which perhaps 96% of species disappeared. Nearly 90% of marine species and 65% of reptile species went extinct at this time. Insects also suffered their greatest mass extinction in Earth’s history.

The P/T boundary provides significant fossil evidence of insect-plant interactions before and after the extinction. The distribution of distinct damage types above and below the boundary provides a pattern in which Permian herbivorous insects were largely consuming leaves from the outside, whereas Triassic species were partitioning plant tissues from within, typically as leaf miners, gallers, and seed predators.

Damaged Plants Reveal Insect Behavior

Dicroidium crassinervisPlants and insects, the two most diverse macroscopic groups of organisms, have long been associated. As early as the Devonian Period (410 million years ago), fossil evidence shows that insects used plants, primarily through external stem feeding and spore consumption. The ways in which insects used plants has increased over time, shifting from mostly leaf chewing to include piercing-and-sucking, galling, and leaf mining.

Dr. Conrad Labandeira, research scientist and curator of fossil arthropods in the Department of Paleobiology at the Smithsonian National Museum of Natural History, studies the associations between plants and insect herbivores to better understand the diversity and evolution of these groups of organisms.

Recording presence-absence data in the fossil record for explicitly-defined insect damage types is crucial for understanding the effect of mass extinction events on insect ecological diversity. For insect-mediated damage on plants, there is a rich and underappreciated fossil record of plant fossils that is considerably more abundant and preservationally complete than that of insects themselves, particularly at extinction intervals.

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