Published: July 24, 2012

Brazil 2012 Fieldwork Diary Entry 13: Skeleton!

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

Today was our first day of fieldwork in the Teresina area this year. We decided we would return to the quarry outside of the town of Timon where we found a very interesting fish skull last year. We're just starting to prepare that specimen, so I can't offer many details about it at this point, but it certainly seems to have a lot of potential. Based on that specimen, our expectations were high and the quarry did not disappoint.

Roger Smith examining the rocks forming the wall of a quarry just outside of the town of Timon, a suburb of Teresina. Photo by Ken Angielczyk.

Today was our first day of fieldwork in the Teresina area this year. We decided we would return to the quarry outside of the town of Timon where we found a very interesting fish skull last year. We're just starting to prepare that specimen, so I can't offer many details about it at this point, but it certainly seems to have a lot of potential. Based on that specimen, our expectations were high and the quarry did not disappoint.

Not long after arriving today, Martha Richter literally stumbled across a partial skeleton of a terrestrial vertebrate (or tetrapod) preserved in a few pieces of rock in one of the quarry spoil piles. The main layer of the quarry that is used for paving material is the hard red siltsone that forms much of the vertical walls. However, at the base of the wall and exposed in some other areas is a softer sandstone that is too friable to use for paving, hence the reason that pieces of it are mostly discarded. It's not an exaggeration to say that this specimen is the most exciting that we've found in our two years of fieldwork in the Parnaíba Basin.

Partial skeleton of a tetrapod from the quarry in Timon. The skull is in the upper left portion of the picture. The large, white pieces of bone just behind the skull are likely parts of the animal's shoulders, and parts of vertebrae (or backbones) can be seen extending towards the bottom of the picture. The scale bar is in centimeters. Photo by Ken Angielczyk.

So what is it? First, I'll say that it's not a synapsid. That's a little disappointing, but the specimen is interesting enough that it's easy to get over. Instead, the specimen appears to represent a type of amphibian. As you can see, the specimen has a fairly short, broad skull that lacks the very elongate snout of Prionosuchus. Therefore it is definitely something new to the basin. The size and shape are a bit reminiscent of the little jaw fragment that Domingas found a few days ago, so it might represent that animal. More preparation of both specimens will be necessary to definitely say whether that's the case. Beyond that, there was a lot of discussion of which group of amphibians the specimen might be part of, based on our attempts to interpret the anatomy exposed in the specimen. A couple of our guesses focused on two groups, the microsaurs and the amphibamids. Both are known exclusively from areas in the northern hemisphere during the Permian, so finding one south of the paleo-equator would be an important discovery. Again, more preparation of the specimen will be necessary to be sure, and we're all already thinking about what might be the best ways to approach this process. Every specimen is a unique problem when it comes to preparation, and the way this one is preserved suggests it will require a particularly delicate touch.

Luckily, the excitement of finding the skeleton was enough to keep us motivated for they rest of the day. It was very hot today (even by local standards), and the only other fossils we found in the quarry during the rest of our searching were small, unidentifiable fragments of bone. The plan for tomorrow is to do more prospecting for fossils in a couple of other quarries in the area. Our discovery today has given us an idea of what rock layer will be good to target, and it would be great if we can find more material like this.


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.