Paleontology Field Research in Paraguay
Studying Future Fossils in the Pilcomayo River Megafan
A collaboration between:
What are the goals of this research?
Paleontologists sometimes struggle to fully understand the lives of ancient creatures. Dr. Jason Moore of the University of New Mexico, the lead researcher on our project, wondered if scientists had been studying the wrong types of modern environments.
Most modern landscapes that paleontologists study erode quickly and don’t preserve bones well. We wondered if megafan river systems, where sediment constantly builds up, might be closer to the type of environment that ancient creatures lived in.
To explore this hypothesis, our international team has spent three years studying how bones are preserved in the megafan system of the Pilcomayo River in Paraguay. We think that the ‘future fossils’ currently being preserved in the Pilcomayo River system will offer important insights. The research team is running a partner study at Petrified Forest National Park in Arizona. We think that comparing the ‘future fossils’ from the Pilcomayo to ancient fossils will help paleontologists better understand ancient ecosystems and the where, what, and why of fossil preservation. We are studying the present to better understand the past.
Who is involved in the research?
This is a global, multi-institutional, long-term project. 2025 will be the 4th year of field work. The research team is composed of scientists and students from the University of New Mexico, Paraguay’s Universidad Nacional de Asunción (National University of Asunción), and the Grand Rapids Public Museum.
For the 2025 field season, we have scientists from the University of Nebraska State Museum and Argentina’s Universidad Nacional de Río Cuarto (National University of Río Cuarto) joining the expedition.
Where is this field research happening?
Our work is being conducted in Paraguay, a country located centrally in South America and bordered by Bolivia, Argentina, and Brazil. Our field area occurs in the dry Chaco, a semi-arid, subtropical lowland, with open, thorny, low forests and grassy savannas. It is very remote and rural. The dry Chaco takes up more than 60% of Paraguay’s land area, but less than 3% of the country’s population inhabits the space!
The Pilcomayo River megafan is the largest megafan in the world and is relatively undisturbed by human modifications. Since the environments of the Pilcomayo megafan are so similar to environments where extinct creatures lived, examining bones on the Pilcomayo megafan will help paleontologists better understand the fossil record and reconstruct ancient ecosystems. We are studying the Pilcomayo Megafan River System at two locations, Pozo Hondo and General Diaz.
Check out our schedule overview for the 2025 field season, June 26 – July 15.
- Asunción – This is Paraguay’s capital and major airport location. We fly into this city and spend 1-2 days packing for the field. We are in remote areas, so we have to bring everything with us–food, water, camping supplies, and any scientific tools. No running to the store or ordering something on Amazon!
- Pozo Hondo – We complete 4 full days of field work here. This site is near the start of the Pilcomayo megafan.
- Cerro Cabrera – We will be helping our Paraguayan colleagues from the Universidad Nacional de Asunción in the Facultad de Ciencias Exactas y Naturales (Faculty of Exact and Natural Sciences) explore a remote rock outcrop and look for vertebrate fossil remains, which are rare in Paraguay.
- Filadelfia – A stop in this city allows us to resupply food and water on our way to our next field area.
- General Diaz – We complete 5 full days of field work in General Diaz. We are interested in this site because it is near the end of the megafan (sediment deposited by the river’s megafan currently stops here).
- Asunción – Return for wrap-up logistics and a celebratory dinner before traveling home.
What are we doing when we are in the field?
Taphonomy is the study of what happens to the remains of an organism between its death and being discovered as a fossil. Usually, only the hardest parts of an organism–bones, teeth, and shells–are preserved as fossils.
We spend our days doing “bone walks,” walking transect lines in search of these skeletal elements. We record consistent fields of data, mark a GPS waypoint, and take photographs of each element. We revisit these ‘future fossils’ year after year to see if they have been moved from one place to another, if they have broken or deteriorated, and how fast they are being buried.
A microsite is a location that produces an abundance of small, disarticulated skeletal elements, less than 10 centimeters in size. Vertebrate fossil microsites are important for reconstructing ancient ecosystems because they contain a diversity of species of various body sizes and produce the large sample sizes needed for quantitative analyses. While fossil microsites can be common in the terrestrial rock record, a modern microsite deposited by a river has never been found. Our goal was to find some!
How do we sample modern vertebrate microsites?
- Look for a promising spot to dig! GRPM’s Dr. Cory Redman, an expert in microsites, searches for layers that look very similar to the fossil-producing microsites seen in the rock record. Typically, these are sediment layers that have a wide variety of grain sizes and organic matter.
- Gather a sample. With shovels, we carefully collect sediment samples from any promising-looking layers.
- Screen wash. We gently wash the sediment samples in water using a set of nested screens. We try to wash away as much of the sediment as possible, leaving only bones and plant remains.
- Dry & Pick – After the sample has dried out, we examine it under a microscope. All of the small bone elements are picked out, identified, and sorted by the type of animal they came from.
Geomorphology is the study of how a landscape changes through time. We are interested in how the Pilcomayo River changes seasonally and how it has changed throughout its history. These factors influence bone preservation into ‘future fossils.’
Drones provide us with high-resolution imagery of surface features. This helps us document changes in the Pilcomayo River and map its sub-environments, such as dry channels, floodplains, and levees. Then, we can look for patterns and consider how ‘future fossils’ are being preserved in different parts of the river.
Sedimentology is the study of how sediments are created through weathering, transportation, and deposition. Stratigraphy is the study of sediment layers and how they change through time. In the field, we dig lots of holes or trenches to closely examine the different layers of sediment in cross sections, recording data such as grain size, color, and structure.
Starting in this 2025 field season, we will install cameras throughout our study site, allowing us to track the distribution and abundance of animals living on the Pilcomayo megafan surface today. This will give us information about the behaviors and patterns of living organisms, helping us form conclusions about what ancient ecosystems in similar megafan environments may have been like.
What have you learned from this research so far?
The goal is for this to be a long-term project (10+ years), but our early work is already telling us a lot about how ‘future fossils’ are being preserved in a modern environment. The Pilcomayo megafan river in Paraguay is giving us interesting insights about fossil assemblages from hundreds of millions years ago.
There are many ‘future fossils’ being preserved in different areas of the Pilcomayo megafan.
Excitingly, overall patterns from ‘future fossil’ data in the Pilcomayo Megafan River System seems to match much of the fossil record, like at Petrified Forest National Park. We will continue exploring more complex patterns on a site-by-site basis.
The Pilcomayo River floods each year during the wet season in Paraguay, laying down huge levels of sediment in a short amount of time. We have seen 5 feet of sediment deposited in a matter of days! This makes it possible for the complete skeleton of a large animal to be buried and preserved. This could help explain how large, intact dinosaur skeletons were preserved so well in the fossil record.
In the 2023 field season, a modern microsite was found and findings were replicated in 2024 with additional microsites. To the best of our knowledge, this project is the first to document a modern microsite in a modern river system! We are still analyzing the skeletal elements from these microsites, but we have already found many bones from every vertebrate group–mammals, birds, fish, reptiles, and amphibians.
Where can we learn more about this work?
1. Stay Connected via Social Media
2. Explore presentations of this work from the Society of Vertebrate Paleontology Annual Conferences
- Modern Vertebrate Taphonomy on the Pilcomayo Distributive Fluvial System in Paraguay as a Model for the Terrestrial Fossil Record (2023)
- Where Have All the Good Bones Gone? Comparing Modern and Fossil Vertebrate Preservation under the Fluvial Megafan Model (2024)
- The Trace Assemblage of the Pilcomayo Megafan and Insights into the Terrestrial Trace Fossil Record