INTERESTING
Ken Angielczyk, an assistant curator at the Field Museum of Natural History, is searching for fossils of ancient mammal relatives in northeastern Brazil.
Saturday, April 14
The Latin phrase "ex libro lapidum, historia mundi" means "from the book of rocks, the history of the world." It is a motto that a geology professor I had in graduate school adopted for himself. It's also a good description for our activities today, our first full day of fieldwork in the Parnaíba Basin.
We arrived last night at one of the main areas we'll be focusing on this year, near the town of Pastos Bons (meaning "good pastures"). This area is where the first specimen of Prionosuchus — an archaic amphibian that lived at the time the Pedra de Fogo Formation was being deposited — was found, and we worked here last year during our reconnaissance trip to the basin. However, Roger Smith (more on Roger and other team members below) wasn't on last year's trip, and we were quite interested in his interpretation of the rock sequences in the area. Therefore, we spent most of the day looking at the structure and composition of the sedimentary rocks preserved in the area to learn about the environmental conditions under which they were likely. Also important was the order in which different rocks occur, which provides information about how the environment was changing over time.
We saw a lot of evidence today that suggests that many of the rocks were formed in conditions in which water was present, but in which the climate was probably quite dry. For example, the picture below shows very large shrinkage cracks that most likely formed as mud covered by shallow water shrank as it started to dry up. Later the cracks were filled in with slightly younger sediments, preserving them as structures in the rock that eventually formed from the sediments.
We also saw rocks that were derived from sand dunes; minerals like gypsum that normally form when water evaporates, leaving its dissolved salts behind; and evidence of mats of cyanobacteria that were living on the surface of the mud. Taken together, the book of rocks we were reading today suggests that the environment was most likely a sabkha, a setting commonly found along ocean margins in hot, dry environments. Good examples of sabkhas can be found along the Red Sea today. In this particular area, the environment probably became more terrestrial as time passed, with rocks representing the dunes along the margin of the sea occurring above rocks formed in the shallow water just at its edge (in most situations rocks occurring higher in a sequence formed after those lower in the sequence).
Although this environment might sound hostile, we did find some fossils at the end of the day that demonstrate that animals were living in the area. A lot of the fossils are fragmentary remains of fish, but there is also a specimen that we think is part of a vertebra (backbone) that may be from a terrestrial vertebrate (also known as a tetrapod). We're not sure if it's from an archaic amphibian, reptile or synapsid, but it gives us hope of finding other tetrapod specimens in the area.
Working with people who have had various experiences and who come from different parts of the world is one of the many things I love about being a paleontologist. Once, I almost threw away what seemed to be an undiagnostic fossil bone fragment that I found while doing fieldwork in Tanzania. But luckily one of my collaborators recognized it as part of a femur (thigh bone) of a dinosaur relative. It was one of the first of many specimens we found that day from that animal, which we later described and named Asilisaurus kongwe. Asilisaurus is one of the most important things we found on that trip; it indicates that the origin of dinosaurs occurred about 10 million years earlier than previously thought.
My team members here are interested in Permian paleontology, but we each bring different research interests and experiences to the Parnaíba project. This combined expertise helps us interpret the fossils we find and the data we collect, so I'd like to introduce you to the team.
I'll start with myself. I work in the Department of Geology at the Field Museum of Natural History in Chicago. My research focuses on a group of therapsids called dicynodonts. Dicynodonts were the most diverse and abundant herbivores in terrestrial communities for much of the Permian and Triassic periods of earth history, so they're important for understanding how those communities functioned ecologically and how they were affected by the end-Permian mass extinction, also known as the largest mass extinction in earth history.
Juan Carlos Cisneros works at the Federal University of Piauí in Teresina, Brazil, which lies conveniently within the Parnaíba Basin. Juan's research focuses on a group of extinct reptiles called procolophonoids, although he's also worked on therapsids and even mammals. Juan recently discoveredTiarajudens, a therapsid, in the Permian of Brazil.
Jörg Fröbisch works at the Leibniz Institute for Research on Evolution and Biodiversity at the Humboldt University of Berlin. Jörg is one of the few other people in the world who has intensively studied dicynodonts, and he recently spent two years working with me at the Field Museum. His current research involves studying how the major groups of therapsids are related, a topic that has received surprisingly little attention from paleontologists.
Christian Kammerer, also based in Berlin, is a postdoctoral researcher working with Jörg. Christian was a graduate student at the University of Chicago during the time Jörg was at the Field Museum, and the three of us recently completed a large work on the dicynodont Dicynodon that we began at that time. Christian has experience studying broad evolutionary patterns in synapsids and has done detailed work on several synapsid subgroups.
Claudia Marsicano is based at the University of Buenos Aires. Her research focuses on the large, often crocodilelike archaic amphibians that were common members of Permian and Triassic communities. This expertise is especially important for our fieldwork because the only terrestrial vertebrate currently known from the Pedra de Fogo Formation is an archaic amphibian called Prionosuchus plummeri. Fossil footprints are another of Claudia's interests.
Martha Richter works at the Natural History Museum in London, and she specializes in fossil sharks and bony fish from the Permian period. She's a key member of the team because most of the vertebrate fossils found in the Pedra de Fogo Formation are bony fish and shark remains, and she also has previous experience doing fieldwork in the Parnaíba Basin. If I get any of the names of fossil fish we find right in future posts, it will be because Martha is reading over my shoulder.
Roger Smith works at the Iziko South African Museum in Cape Town, and much of his research focuses on sedimentology (i.e., using the structure and composition of sedimentary rocks to understand the environments in which they formed) and taphonomy (i.e., the study of the processes by which animal remains are preserved as fossils). He's also done a ton of fieldwork in the Permian all over the world, and is one of the most skilled fossil finders I know. Most of the paleontology exhibit at the Iziko South African Museum is a testament to Roger's ability to find amazing specimens, and if we do discover any synapsids on this trip, it wouldn't surprise me if Roger is the first to find them.
Finally, Jeff Johnson is a videographer who is accompanying us in the field. Jeff will be taking photos and videos of us as we do our work, which we use for making short educational videos.
Now that we have a better idea of what the rocks are telling us, our plan for tomorrow is to explore some new outcrops near where we we found today's fossils. Part of what we'll do is to see how the rocks there fit in with the interpretation that Roger started developing today. Our main goal, though, will be to devote more effort toward finding fossils. Hopefully we'll have good results.
__._,_.___
No comments:
Post a Comment