From First Grade to the Field Museum: A Paleontologist's Research Comes Full Circle

October 12, 2012

Ken Angielczyk, MacArthur Curator of Paleomammalogy and Section Head, Negaunee Integrative Research Center

If you take sample of paleontologists and ask them how they became interested in the field of paleontology, some of them will doubtlessly tell you that they first got hooked on dinosaurs as a kid and things proceeded from there. I am definitely an example of this phenomenon: as far back as I can remember I was fascinated by dinosaurs, and “paleontologist” was almost always the answer when people asked what I wanted to be when I grew up. Even though my research now focuses on ancient mammal relatives that lived before the dinosaurs, I've been very fortunate to be able to realize my childhood dream and be a paleontologist. Recently, however, I've been involved in a research project that has literally taken me back to my childhood.

The Asteroid and the Dinosaurs

In June, 1980, Luis Alvarez, Walter Alvarez, Frank Asaro, and Helen Michel published a seminal paper in the scientific journal Science, in which they presented evidence of an asteroid impact at the end of the Cretaceous Period of Earth History (about 65 million years ago). They also hypothesized that the after-effects of this impact caused the end-Cretaceous mass extinction, whose victims famously include the non-avian dinosaurs. Extensive research over the last three decades has led to the impact hypothesis becoming the generally accepted explanation for the ultimate cause of the end-Cretaceous extinction (Schulte et al., 2010), but in 1980 it was an extremely controversial idea and it generated a lot of attention in the popular media. A fascinating, first-hand account of the story behind this discovery and the scientific debates that ensued can be found in Walter Alvarez's book T. rex and the Crater of Doom.

The 1982 Williamstown Elementary School Science Fair

In 1982 I was six years old and in first grade. Being a kid that loved dinosaurs, when the yearly science fair rolled around, I naturally wanted my project to focus on that topic. I don't remember where exactly I got the idea, I must have seen it on Nova or in a magazine, but I decided I would do my project on the recent discovery that an asteroid killed the dinosaurs. You can see the two parts of my poster in the photos below (thanks to my parents for saving them all these years!). The main point of the poster was describing how the asteroid impact could have killed the dinosaurs: dust and debris blasted into the atmosphere by the impact would have blocked sunlight from reaching the Earth's surface. Without sunlight plants would die off, and the loss of this food source would cause plant-eating dinosaurs to go extinct. In turn, meat eating dinosaurs also would go extinct as the herbivores that were their food source disappeared. I didn't think of it in these terms at the time, but the process described in my poster reflects how disturbances to one part of a community of organisms can spread along the links in the community's food web, causing animals and plants that were not involved in the initial disturbance to nonetheless become extinct. After the science fair, I didn't think much about these ideas for quite some time.

The Circle Begins to Close

We'll now fast-forward to about the year 2001. At the time, I was a graduate student working on my Ph.D. at the University of California, Berkeley. UC Berkeley has a strong paleontology program, and I was a student in Dr. Kevin Padian's lab working on a group of ancient mammal relatives called dicynodonts. My research project focused on reconstructing how the various dicynodont species were related to each other, and using those relationships as a framework to study the evolutionary history of the group. Dicynodonts lived in the Permian and Triassic periods of Earth history, and as such they were witnesses to and survivors of the end-Permian mass extinction. This extinction event is the largest in Earth history, and it occurred about 250 million years ago. Dr. Walter Alvarez was (and is) a professor in the Department of Earth and Planetary Science at UC Berkeley, and by the time I was a graduate student his interests in mass extinctions had expanded from just the end-Cretaceous extinction to include the end-Permian extinction as well. My work didn't focus on how the end-Permian event affected dicynodonts, but Walter's knowledge of things Permian made him a good choice to have as a member of my dissertation committee. I ended up taking a couple of classes with him and in 2003, some 21 years after my first grade science fair project, he was one of the people who read and signed off on my Ph.D. dissertation (thanks Walter!). I'm not sure what my six-year-old self would have thought if you told him that someday he would know the person who played a key role in discovering that an asteroid impact caused the end-Cretaceous extinction and have him as a mentor in the process of becoming a paleontologist. But that's not the end of the story.

Food Webs and Extinction

After I graduated from UC Berkeley, I spent about two and a half years working as a postdoctoral researcher at the California Academy of Sciences with Dr. Peter Roopnarine, one of the museum's curators. Peter is a paleoecologist (i.e., he is interested in understanding the ecological relationships of past organisms and how and why those relationships change over time). During the time that I was at the Academy, Peter became interested in network theory and how it could be applied to scientific questions that he was interested in. We tried a few different network-based projects, but the one that really got going was using network theory to model how disturbances can propagate through a community's food web, causing plants and animals to become extinct. Peter developed a model called CEG (Cascading Extinction on Graphs) to examine this problem, and I contributed data about the food webs of several Permian and Triassic communities from South Africa that included many dicynodonts. One of the things that we discovered in the course of that work is that the earliest Triassic community in South Africa, which existed just after the end-Permian extinction, had a very unusual food web structure that made the community relatively unstable (Roopnarine et al., 2007; Roopnarine and Angielczyk, 2012). Much of Peter's research has subsequently focused on figuring out why the structure of the community made it unstable, and I've continued to work with him on the implications of the model results for dicynodonts and other animals that were alive at the time. This research also inadvertently brought me a step closer to my first grade project: I was now studying the link between food webs and extinctions, although I wasn't yet paying attention to the end-Cretaceous extinction.

Full Circle

Since 2007, I've worked at The Field Museum. My research continues to focus on topics such as how dicynodonts are related to each other, and how food web structures might have affected the end-Permian extinction. About two years ago, I started working with a Ph.D. student at the University of Chicago named Jonathan Mitchell. Jon is interested in the paleoecology of birds, and as part of his Ph.D. project he is planning on studying how birds affect the food web structures of certain ancient and modern communities. When he started at U of C, Jon was interested in incorporating the CEG model into some of his work, and he began working on a project looking at the food web structures of some Cretaceous communities that included birds and dinosaurs. As things progressed, we decided that it would be interesting to try to determine if the food web structures of communities at the end of the Cretaceous were such that they might have made the extinction resulting from the asteroid impact worse than it might otherwise have been. In other words, one of the expected consequences of the impact is a die off of plants, so did the food web structures of latest Cretaceous communities allow that disturbance to easily spread to other members of the communities, causing additional extinctions? As we show in a paper that was published in the journal Proceedings of the National Academy of Sciences (Mitchell et al., 2012), the short answer is yes: the food web structures of latest Cretaceous communities in North America did make them more vulnerable than communities from a few million years earlier. So if the asteroid hit 75 million years ago instead of 65 million years ago, it probably would have still caused a mass extinction, but that hypothetical extinction likely would not have been as severe as the one that actually happened.

In participating in this work, and in writing this paper, my research has truly come full circle. My first science fair project was about how the effects of the asteroid impact at the end of the Cretaceous could have spread through food webs, causing extinction, and now I'm a co-author of a research paper that addresses essentially the same question (albeit in a somewhat more sophisticated way). Even as a paleontologist, I wouldn't have predicted that this would happen given the focus of my research (ancient mammal relatives that lived before the dinosaurs). However, one of the rewarding things about being a scientist is that you get to follow where your curiosity leads, and sometimes it takes you to unexpected places. And now when someone asks me about why the dinosaurs went extinct at the end of the Cretaceous Period, I can tell them that it's a question I've been working on for practically my whole life…

References

Alvarez, L.W., W. Alvarez, F. Asaro, and H. V. Michel. 1980. Extraterrestrial cause for the Cretaceous-Tertiary Extinction. Science 208: 1095-1108.

Alvarez, W. 1997. T. rex and the Crater of Doom. Princeton: Princeton University Press.

Mitchell, J.S., Roopnarine, P.D., and Angielczyk, K.D. 2012. Late Cretaceous restructuring of terrestrial communities facilitated the end-Cretaceous mass extinction in North America. Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.1202196109

Roopnarine, P.D. and Angielczyk, K.D. 2012. The evolutionary palaeoecology of species and the tragedy of the commons. Biology Letters 8: 147-150.

Roopnarine, P.D., Angielczyk, K.D., Wang, S.C., and Hertog, R. 2007. Food web models explain instability of Early Triassic terrestrial communities. Proceedings of the Royal Society Series B 274: 2077-2086.

Schulte, P., Alegret, L., Arenillas, I., Arz, J.A., Barton, P.J., Bown, P.R., Bralower, T.J., Christeson, G.L., Claeys, P., Cockell, C.S., Collins, G.S., Deutsch, A., Goldin, T.J., Goto, K., Grajales-Nishimura, J.M., Grieve, R.A.F., Gulick, S.P.S, Johnson, K.R., Kiessling, W., Koeberl, C., Kring, D.A., MacLeod, K.G., Matsui, T., Melosh, J., Montanari, A., Morgan, J.V., Neal, C.R.22, Nichols, D.J., Norris, R.D., Pierazzo, E., Ravizza, G., Rebolledo-Vieyra, M., Reimold, W.U., Robin, E., Salge, T., Speijer, R.P., Sweet, A.R., Urrutia-Fucugauchi, J., Vajda, V., Whalen, M.T., Willumsen, P.S. 2010. The Chicxulub asteroid impact and mass extinction at the Cretaceous-Paleogene boundary. Science 327: 1214-1218.

Ken Angielczyk

MacArthur Curator of Paleomammalogy and Section Head

I am a paleobiologist interested in three main topics: 1) understanding the broad implications of the paleobiology and paleoecology of extinct terrestrial vertebrates, particularly in relation to large scale problems such as the evolution of herbivory and the nature of the end-Permian mass extinction; 2) using quantitative methods to document and interpret morphological evolution in fossil and extant vertebrates; and 3) tropic network-based approaches to paleoecology. To address these problems, I integrate data from a variety of biological and geological disciplines including biostratigraphy, anatomy, phylogenetic systematics and comparative methods, functional morphology, geometric morphometrics, and paleoecology.

A list of my publications can be found here.

More information on some of my research projects and other topics can be found on the fossil non-mammalian synapsid page.

Most of my research in vertebrate paleobiology focuses on anomodont therapsids, an extinct clade of non-mammalian synapsids ("mammal-like reptiles") that was one of the most diverse and successful groups of Permian and Triassic herbivores. Much of my dissertation research concentrated on reconstructing a detailed morphology-based phylogeny for Permian members of the clade, as well as using this as a framework for studying anomodont biogeography, the evolution of the group's distinctive feeding system, and anomodont-based biostratigraphic schemes. My more recent research on the group includes: species-level taxonomy of taxa such as Dicynodon, Dicynodontoides, Diictodon, Oudenodon, and Tropidostoma; development of a higher-level taxonomy for anomodonts; testing whether anomodonts show morphological changes consistent with the hypothesis that end-Permian terrestrial vertebrate extinctions were caused by a rapid decline in atmospheric oxygen levels; descriptions of new or poorly-known anomodonts from Antarctica, Tanzania, and South Africa; and examination of the implications of high growth rates in anomodonts. Fieldwork is an important part of my paleontological research, and recent field areas include the Parnaíba Basin of Brazil, the Karoo Basin of South Africa, the Ruhuhu Basin of Tanzania, and the Luangwa Basin of Zambia. My collaborators and I have made important discoveries in the course of these field projects, including the first remains of dinocephalian synapsids from Tanzania and a dinosaur relative that implies that the two main lineages of archosaurs (one including crocodiles and their relatives and the other including birds and dinosaurs) were diversifying in the early Middle Triassic, only a few million years after the end-Permian extinction. Finally, the experience I have gained while studying Permian and Triassic terrestrial vertebrates forms the foundation for work I am now involved in using models of food webs to investigate how different kinds of biotic and abiotic perturbations could have caused extinctions in ancient communities.

Geometric morphometrics is the basis of most of my quantitative research on evolutionary morphology, and I have been using this technique to address several biological and paleontological questions. For example, I conducted a simulation-based study of how tectonic deformation influences our ability to extract biologically-relevant shape information from fossil specimens, and the effectiveness of different retrodeformation techniques. I also used the method to address taxonomic questions in biostratigraphically-important anomodont taxa, and I served as a co-advisor for a Ph.D. student at the University of Bristol who used geometric morphometrics and finite element analysis to examine the functional significance of skull shape variation in fossil and extant crocodiles. Focusing on more biological questions, I am currently working on a large geometric morphometric study of plastron shape in extant emydine turtles. To date, I have compiled a data set of over 1600 specimens belonging to nine species, and I am using these data to address causes of variation at both the intra- and interspecific level. Some of the main goals of the work are to examine whether plastron morphology reflects a phylogeographic signal identified using molecular data in Emys marmorata, whether the "miniaturized" turtles Glyptemys muhlenbergiiand Clemmys guttata have ontogenies that differ from those of their larger relatives, and how habitat preference, phylogeny, and shell kinesis affect shell morphology.

A collaborative project that began during my time as a postdoctoral researcher at the California Academy of Sciences involves using using models of trophic networks to examine how disturbances can spread through communities and cause extinctions. Our model is based on ecological principles, and some of the main data that we are using are a series of Permian and Triassic communities from the Karoo Basin of South Africa. Our research has already shown that the latest Permian Karoo community was susceptible to collapse brought on by primary producer disruption, and that the earliest Triassic Karoo community was very unstable. Presently we are investigating the mechanics that underlie this instability, and we're planning to investigate how the perturbation resistance of communities as changed over time. We've also experimented with ways to use the model to estimate the magnitude and type of disruptions needed to cause observed extinction levels during the end-Permian extinction event in the Karoo. Then there's the research project I've been working on almost my whole life.

Morphology and the stratigraphic occurrences of fossil organisms provide distinct, but complementary information about evolutionary history. Therefore, it is important to consider both sources of information when reconstructing the phylogenetic relationships of organisms with a fossil record, and I am interested how these data sources can be used together in this process. In my empirical work on anomodont phylogeny, I have consistently examined the fit of my morphology-based phylogenetic hypotheses to the fossil record because simulation studies suggest that phylogenies which fit the record well are more likely to be correct. More theoretically, I developed a character-based approach to measuring the fit of phylogenies to the fossil record. I also have shown that measurements of the fit of phylogenetic hypotheses to the fossil record can provide insight into when the direct inclusion of stratigraphic data in the tree reconstruction process results in more accurate hypotheses. Most recently, I co-advised two masters students at the University of Bristol who are examined how our ability to accurately reconstruct a clade's phylogeny changes over the course of the clade's history.

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