Researchers at UNAM’s FES Zaragoza have formally described a new fossil axolotl species, Ambystoma quetzalcoatli, in the state of Hidalgo. The find is the first fossil salamander species formally described in Mexico and the oldest known record of the genus Amb
For years. the fossils lay quietly in collections—salamander bones collected in the early 2000s. preserved well enough to show complete. articulated skeletons. Then a new look with modern tools turned those remains into something Mexico had never had before: a formally described fossil salamander species.
The new species is named Ambystoma quetzalcoatli. Researchers at the Zaragoza School of Advanced Studies (FES Zaragoza) at the National Autonomous University of Mexico (UNAM) identified it from fossil material found in the municipality of Atotonilco el Grande, in the state of Hidalgo.
This discovery is significant beyond a single name on a label. It is the first fossil salamander species to be formally described in Mexico. and it represents the oldest known record of the genus Ambystoma ever documented in the country. In other words. it pushes Mexico’s timeline for this group further back than previously established—right in the region where ancient freshwater life once clustered around an almost vanished world.
The fossil site sits in a landscape that was once part of an extensive freshwater lake system. covering roughly 85 square kilometers. The lakes likely formed when the course of the Amajac River was temporarily blocked. That temperate. subhumid environment has produced fossils of numerous plants and a range of aquatic and land-dwelling life. including diatoms. gastropods. ostracods. beetles. and fish.
Yet until now, the amphibian remains recovered from the site had not been formally studied or described.
The scientists examined a dozen fossil salamander specimens collected by the FES Zaragoza Paleobotany Research Group. Many of them were exceptionally well preserved, including complete, articulated skeletons that could be studied for anatomy and morphology in fine detail.
Initially, the fossils were identified as belonging to a species in the genus Ambystoma—the group that includes modern axolotls. But the material was revisited nearly three decades later by a team led by Jorge Herrera Flores and María Patricia Velasco de León. This time. the work used computed tomography (CT) scanning and detailed anatomical comparisons with living species to refine what the fossils actually represented.
Their conclusion: the specimens belonged to an entirely new species. The study says the fossils are distinguished from modern axolotls by several significant anatomical differences, especially in features of the skull and skeleton that are absent in living species.
Among the most notable traits is an elongated opening on the top of the skull. The fossils also show a differently structured palate. variations in the arrangement of several cranial bones. and a key count difference in the backbone: the fossils include 17 trunk vertebrae. Modern axolotls have 16 or fewer trunk vertebrae.
To pin down identity. the researchers compared the fossils with 13 living Ambystoma species—including several endemic to Mexico such as the Xochimilco axolotl (Ambystoma mexicanum)—and also with tiger salamanders from Mexico and the United States. The comparisons relied on three-dimensional imaging and CT scans available through international scientific collections.
The findings were published in Palaeontologia Electronica.
Taken together, the work doesn’t just add a new axolotl to the scientific record. It reframes a slice of Mexico’s deep ecological history—turning overlooked amphibian remains from an old lake system into evidence that helps explain how the biodiversity tied to modern Mexican fauna may have taken shape over time.
UNAM FES Zaragoza Ambystoma quetzalcoatli fossil axolotl Hidalgo Atotonilco el Grande Palaeontologia Electronica computed tomography CT scanning Ambystoma Xochimilco axolotl paleontology evolution