Amazonia's Hidden Earthworks Uncovered by LiDAR and a New Cephalopod Fossil Push Back Evolution

Overview

The Nature Podcast this week presents two intertwined scientific stories. First, LiDAR surveys in the southwest Amazon reveal a sprawling network of ancient earthworks attributed to the Acuri civilization, challenging the view of precolonial Amazonia as sparsely populated. Second, a fossil described by Jakub Winter could push back the origin of cephalopods by roughly 20 to 25 million years, offering a glimpse into early mollusk evolution.

Key insights

• LiDAR mapping uncovers about 430 earthworks with around 400 new sites in the Acri and Amazonas region, suggesting a highly organized, urbanized precolonial landscape.
• Extrapolations place the Aquari/Acuri civilization across more than 180,000 square kilometers at its peak, with population estimates between 1.25 and 3 million people.
• Deforestation and aerial/satellite imagery enabled the discovery of earthworks long hidden by forest cover, highlighting the importance of advanced remote sensing in archaeology.
• A new Cambrian fossil with a siphuncle suggests buoyancy control and potential early predation, pushing cephalopod origins earlier than previously thought.

Overview

This episode of Nature Podcast features two major stories that illuminate different chapters of Earth’s deep past. The first centers on the Amazon, where researchers studying the region around Acri and Amazonas state have uncovered a vast landscape of ancient earthworks attributed to a prehistoric civilization researchers are calling the Acuri. The second story takes us far back in time to the Cambrian period, where a new cephalopod fossil described by Jakub Winter and colleagues may extend the cephalopod lineage deeper than the previous earliest fossil evidence. Together, these narratives underscore how modern techniques such as LiDAR and careful fossil interpretation can rewrite long standing assumptions about where and how ancient people lived and how early animals evolved.

Amazonia Revisited: The Acuri Earthworks

The main landscape story takes the listener to the southwest corner of the Amazon, near the tri-border region of Brazil, Peru, and Bolivia. Researchers Marty Parsanen and colleagues have been studying this region, where a civilization they are calling the Acuri inhabited the landscape between roughly 700 BCE and 900 CE. The team’s reasoning for the name Acuri lies in using the Accure river as a cultural shorthand, since the people themselves left no known self appellation in the historical record discovered so far. The work builds on earlier findings of earthworks—large mounds and dirt troughs that formed roads and geoglyphs across vast tracts of land, some spanning multiple hectares. Prior identifications already suggested more than a thousand sites, but a central mystery remained: how extensive were these engineered landscapes and what functions did they serve?

Recent efforts used high technology to see what lay beneath the forest canopy. While many earthworks had been identified using aerial photography and satellite imagery in deforested patches, more than half of the Acre and Amazonas areas remained shrouded by forests. The researchers secured permission to deploy plane based LiDAR systems, which emit laser pulses and map 3D ground topography with high resolution. The resulting campaigns surveyed around four and a half thousand square kilometers, revealing a bounty of previously unseen earthworks. In total, the team identified about 430 earthworks, with roughly 400 of these being new discoveries. A large portion appeared as chalk leaf like shapes, many with ditches, and the team also cataloged a network of roads that connected these features, hinting at coordinated planning and administration across the landscape.

Radiocarbon sampling and other evidence were used to place the origins and duration of the earthworks. More than 160 radiocarbon samples constrain the first geocliffs to around 600 BCE, with construction tapering off around 650 CE. While not all earthworks could be attributed to the Acuri and some likely predated or postdated their occupation, the combined data allow researchers to extrapolate a broader regional story. By combining their LIDAR data with previously collected evidence, the team estimates the Aquari civilization’s extent to more than 180,000 square kilometers, a figure that tripled Marty Parsanen’s earlier estimates. When density is considered, the team arrived at a count estimate of 24,000 to 30,000 earthworks in total within the expanded area.

The implications of these numbers are profound. If the Acre region and adjacent Amazonia contained hundreds of thousands of earthworks and millions of inhabitants, the Amazon was an urbanized region long before European contact. This perspective dovetails with other botanical and ecological clues suggesting domestication or management of certain trees such as Brazil nuts, indicating cultural influence on biodiversity and soil patterns. The researchers also acknowledge the limitations and the necessary caveats. The LIDAR survey covered about 3% of the broader Amazonian region, and there is a question of how representative the four and a half thousand square kilometers are for the entire basin. Nevertheless, the findings argue against the longstanding view of precolonial Amazonia as a largely pristine, sparsely populated wilderness. The vision of a region punctuated by urban centers and complex socio cultural networks adds new dimensions to discussions of population dynamics and environmental impact in the premodern world.

Cost is a practical barrier to expanding LiDAR campaigns. The researchers note that future campaigns could be ten times larger than the ones described here, but the cost will be a limiting factor. As the team contemplates expanding to other areas, there is a sense of cautious optimism to develop new campaigns and gather more robust data. The broader take away is that Amazonia’s history is richer and more densely occupied than previously thought, and the landscape's cultural legacy continues to shape the modern biodiversity and soil composition of the region. This narrative part of the podcast closes with reflections on how the new era of archaeology invites more interdisciplinary collaborations to understand how past peoples interacted with their environments.

Cephalopod Evolution: A Cambrian Bearing Fossil

The second major segment of the program turns to a fossil discovery that fills a critical gap in the cephalopod fossil record. Cephalopods include modern creatures such as squids, octopuses, and nautiluses and their evolutionary history has commonly been traced through shell morphology and the siphuncle, a soft tissue structure that passes through gas or fluid filled chambers in chambered shells. The host of the interview with Jakub Winter details a tiny fossil, conical shells about 4.5 millimeters long, preserved in several ways so that researchers can observe external morphology and internal chamber preservation and also the presence of the siphuncle in some specimens. The age range of the new find is constrained to roughly 515 to 521 million years ago, placing it in the mid Cambrian. This sets the fossil roughly 20 to 25 million years earlier than the oldest cephalopods previously recognized, which were around 490 to 495 million years old. The fossil preservation includes both external shells and examples where the shell is not preserved but the chambered structure is, along with the siphungal tube extending through the chambers. All of these features strengthen the case that the organism is indeed an early cephalopod rather than some other shelled organism with similar deposits.

How certain is this attribution? The researchers make a strong case, noting that the combination of features seen in these fossils is difficult to reconcile with other lineages that also possess conical shells or chambered interiors. However, they acknowledge that evolution can produce convergent features, so while the current evidence makes a compelling argument for cephalopod identity, there remains some room for future reinterpretation as more specimens become available.

What does this mean for cephalopod evolution? The finding suggests that a shell with chambers for buoyancy and a siphuncle materialized very early in the cephalopod stem lineage, almost immediately after cephalopods diverged from other mollusks. This implies that buoyancy control and the ability to lift off the seafloor may have emerged earlier than previously believed, enabling diversification into a broader range of ecological niches and later enabling the predatory tendencies that dominate modern cephalopods. The discussion also touches on how early cephalopods may have looked and how their shells evolved from straight conical forms to the modern chambered designs. The scientists emphasize that these early stages were likely transitional and that modern cephalopods represent a later stage of evolutionary experimentation and specialization.

In closing, Jakub Winter reflects on the broader implications of the fossil: it helps close a gap in the cephalopod record and informs models of how these animals diversified. The podcast highlights show notes with links to further reading and context about early cephalopods and the siphuncle, encouraging listeners to explore the upcoming research and debates in this field. Overall, the two stories together portray a world where modern technology reveals ancient landscapes and lineages that were previously invisible to science, inviting new questions about how humans and nature have shaped each other across time.

Looking Ahead

The episode ends with a reminder that the frontiers of knowledge extend beyond a single discipline. The LiDAR survey represents only a portion of the Amazon basin and is a testament to how advancements in remote sensing can transform archaeology. The cephalopod fossil opens a window into early molluscan life and invites reevaluation of established timelines. The show notes invite listeners to follow up with more details and links to the primary research papers and related work. The overall message is one of renewed curiosity and a readiness to revisit long held assumptions with new data and methods.