Long before the Felipe Ángeles International Airport rose northeast of Mexico City, the land was once covered by Lake Xaltocan, home to a thriving community of prehistoric animals. When construction of the airport began in 2019, the project — already controversial — unexpectedly turned into one of the largest paleontological digs in the region, uncovering the remains of more than 110 mammoths along with fossils from other ancient species.
At first, scientists assumed these mammoths would match the Columbian mammoth (Mammuthus columbi), the only species long believed to inhabit most of North and Central America. The woolly mammoth (Mammuthus primigenius), by contrast, migrated from Eurasia and is more commonly found in Canada and the northern U.S. But the evolutionary history of the Columbian mammoth has always been a little murky.
Earlier research suggested the Columbian mammoth may have been the result of hybridization between woolly mammoths and another Eurasian species, the steppe mammoth (Mammuthus trogontherii), sometime between 800,000 and 400,000 years ago. That theory implied the Mexican fossils would fit neatly within this lineage.
However, a new study published in Science has complicated the story. By analyzing mitochondrial DNA extracted from the teeth of mammoths unearthed at both the airport site and a nearby dig in Tultepec, researchers discovered something unexpected: the Mexican mammoths represent a unique maternal lineage dubbed Clade 1G.
This lineage didn’t just differ from other North American mammoths — it also displayed surprising internal diversity. In fact, the genetic divergence within Clade 1G was as deep as the differences between entirely separate North American mammoth groups.
Scientists offered two possible explanations. One is that genetic sub-structuring already existed within the ancestral woolly mammoth population before it interbred with the steppe mammoth-like Krestovka lineage that gave rise to the Columbian mammoth. Another possibility is that multiple woolly mammoth populations, arriving at different times, each interbred with Krestovka-like ancestors, creating distinct Columbian mammoth lineages. The authors lean toward the first scenario.
Radiocarbon dating placed these Mexican mammoths in the Late Pleistocene, between 40,000 and 12,700 years ago, showing that several divergent lineages coexisted during that time.
For paleontologists, this is a breakthrough. Recovering DNA from fossils in warm climates has long been considered nearly impossible, since genetic material degrades rapidly outside of permafrost. By focusing on mitochondrial DNA — which is more abundant than nuclear DNA — the team was able to retrieve crucial evolutionary clues.
“This study highlights the importance of sampling fossils from broader geographic regions,” the authors concluded, “and proves that even in tropical latitudes, it’s possible to recover valuable genetic data that reshapes our understanding of extinct species.”