In the dusty soil of northeastern Mexico, just a few miles away from Mexico City, construction workers broke ground for what would become the Felipe Ángeles International Airport. But as the earth shifted to make way for the future, something far older than modern engineering was unearthed. The area, once home to the now-defunct Lake Xaltocan, revealed an unexpected treasure trove of ancient bones—hundreds of mammoth fossils.
To paleontologists, the discovery was electrifying. At least 110 individual mammoths had been uncovered, along with the remains of other prehistoric animals. These were not random relics of the past; they held the promise of revealing new insights into the ancient creatures that roamed the Americas long before humans stepped onto the scene.
For decades, paleontologists assumed these mammoths were the same species as those found in North America—the Columbian mammoth (Mammuthus columbi). After all, this species was native to both North and Central America, with the fossil record suggesting they were closely related to the woolly mammoth (Mammuthus primigenius), which had arrived from Eurasia. But the more researchers dug, both literally and figuratively, the more complex the story became.
The Columbian Mammoth: A Shifting Legacy
The Columbian mammoth was long thought to have evolved from the hybridization of two mammoth species: the woolly mammoth and the steppe mammoth (Mammuthus trogontherii). This hybridization, scientists believed, occurred between 800,000 and 400,000 years ago, giving rise to a robust species that dominated the American continent during the Late Pleistocene.
But the mammoths discovered in Mexico, alongside other fossils unearthed at nearby Tultepec between 2016 and 2019, would soon cast doubt on this widely accepted theory. A breakthrough was on the horizon, one that would not only change our understanding of the Columbian mammoth but also offer a rare glimpse into the complexities of ancient DNA.
The Mystery of DNA Preservation
DNA is a fragile thing. For most animals, even a few thousand years can degrade the genetic material to a point where it is unrecognizable. In warmer climates, like those in Mexico, DNA preservation is especially difficult. Tropical heat tends to break down the molecular bonds in genetic material much faster than the cold climates of the north, where mammoths and other Pleistocene creatures are more commonly found.
Yet, against all odds, scientists were able to extract mitochondrial DNA (mtDNA) from the mammoths buried beneath the soil. Unlike nuclear DNA, which is passed down from both parents, mitochondrial DNA is inherited only from the mother, making it an invaluable tool for tracing the maternal lineage of ancient species. Though it provides only a partial snapshot of a species’ genetic makeup, mtDNA can reveal important patterns that help scientists understand the evolutionary history of extinct animals.
A Genetic Revelation
A study published in Science in 2021 turned the conventional wisdom about the Columbian mammoth on its head. By analyzing mitochondrial DNA extracted from the teeth of the mammoths found at the Felipe Ángeles International Airport and Tultepec, researchers uncovered an entirely new lineage. This lineage, dubbed Clade 1G, was distinct from any other known North American mammoth population.
What made this discovery so significant was the genetic divergence found within Clade 1G. In fact, the genetic differences between subgroups of this lineage were just as profound as the divergence between entire mammoth species, such as the Columbian mammoth and the woolly mammoth. This suggested that the Mexican mammoths were not simply a variation of the Columbian mammoth, as many had believed. They were part of a distinct, genetically isolated population.
Two Possible Explanations
So, what did this mean for the origins of the Columbian mammoth? The researchers proposed two possible explanations for this newfound divergence in the mitochondrial lineage:
- Early Structure of M. primigenius: The first hypothesis suggested that the structure of the Columbian mammoth’s mitochondrial lineage existed prior to the hybridization event that led to the formation of the species. This would imply that the maternal ancestors of the Mexican mammoths had a unique, early evolutionary history that predates the Columbian mammoth’s hybrid origin.
- Multiple Hybridization Events: The second hypothesis posited that the distinct lineage of the Mexican mammoths could have arisen from multiple hybridization events between different groups of woolly mammoths, steppe mammoths, and other ancestral mammoth populations. This would imply that the evolution of the Columbian mammoth was more complex than previously thought, with multiple waves of genetic mixing contributing to the species’ diversity.
After much analysis, the researchers leaned toward the first explanation. They argued that the mitochondrial lineage found in the Mexican mammoths likely existed before the hybridization event between woolly and steppe mammoths, giving rise to a genetically distinct population.
The Window into the Past
One of the most exciting aspects of this study was the use of radiocarbon dating to establish the age of the fossils. The dating placed the divergent lineages within the Late Pleistocene, a period that lasted from approximately 40,000 to 12,700 years ago. This time frame is crucial because it coincides with the period when mammoths were roaming North America and interacting with early human populations.
For paleontologists, this discovery is a milestone. The ability to recover DNA from tropical latitudes, such as Mexico, opens up new possibilities for studying species that were previously difficult to analyze. These findings underscore the importance of expanding genetic research into regions that have been overlooked in the past.
The Bigger Picture: Understanding Evolution
This study not only challenges the accepted understanding of the Columbian mammoth’s origins but also sheds light on the broader picture of mammoth evolution. Mammoths were not a monolithic group, but rather a collection of genetically diverse populations, each with its own evolutionary story. By investigating these different lineages, scientists can build a more nuanced understanding of how mammoths adapted to various environments across North America and beyond.
The findings from Mexico provide a rare opportunity to explore the genetic diversity of extinct species, particularly in regions that were previously underexplored. As more ancient DNA is recovered, it may reveal even more surprising twists in the story of mammoth evolution, and by extension, the story of life on Earth.
The Importance of Ancient Genomics
What this study also underscores is the importance of ancient genomics—the field of science dedicated to recovering and analyzing the DNA of long-extinct species. For years, the focus of paleontological research has largely been on fossils—the bones, teeth, and other remains that provide a tangible connection to ancient creatures. But DNA offers an entirely new dimension of understanding, one that can fill in the gaps left by the fossil record.
The study of ancient genomes allows scientists to trace the movements, behaviors, and even the environmental challenges faced by extinct species. It provides insights into how these animals adapted to changing climates, migrated across continents, and interacted with other species. Moreover, it gives us a glimpse into the genetic legacies that some species have left behind, helping us better understand the origins of modern-day animals.
A Future Full of Potential
The mammoths of Mexico were not just ancient giants whose bones were buried beneath the earth—they were a key to unlocking a deeper understanding of the past. Their DNA, carefully preserved in the heat of a tropical climate, is opening doors to new areas of paleontological research and challenging old assumptions about mammoth evolution.
As we look to the future, the study of ancient genomes will likely play an increasingly central role in our understanding of extinct species. The discoveries from Mexico highlight the untapped potential of studying ancient DNA in regions once thought to be unsuitable for preservation. With further research, we may one day solve the puzzle of why these majestic creatures went extinct and how they fit into the broader tapestry of life on Earth.
But for now, the mammoths of Mexico offer us something far more profound: a reminder of how much we still have to learn, how deep the mysteries of the past run, and how, sometimes, a single discovery can change everything we thought we knew about the world.
More information: Eduardo Arrieta-Donato et al, Columbian mammoth mitogenomes from Mexico uncover the species’ complex evolutionary history, Science (2025). DOI: 10.1126/science.adt9651
