Researchers at the Zaragoza School of Advanced Studies (FES Zaragoza) at the National Autonomous University of Mexico (UNAM) have identified a new fossil species of axolotl named Ambystoma quetzalcoatli. This remarkable discovery, made in Hidalgo, marks the first formal description of a fossil salamander species in Mexico and represents the oldest known record of the Ambystoma genus in the country.
The fossils were unearthed in the municipality of Atotonilco el Grande, an area that once featured a vast freshwater lake system. This ancient ecosystem, covering approximately 85 square kilometers, formed when the Amajac River's course was temporarily obstructed. The researchers' findings contribute significantly to understanding the origin and evolution of biodiversity in modern Mexican fauna.
Significance of the Discovery
The discovery of Ambystoma quetzalcoatli provides crucial insights into the evolutionary history of axolotls, suggesting that their lineage extends much further back than previously assumed. The analysis indicates that these amphibians inhabited what is now Mexico during the Pliocene epoch, several million years ago.
According to the study published in Palaeontologia Electronica, the fossils exhibit unique skull and skeletal features not present in living axolotls. These include:
- An elongated opening on the top of the skull
- A differently structured palate
- Variations in cranial bone arrangement
- 17 trunk vertebrae, compared to 16 or fewer in modern axolotls
Research Methodology
The research team, led by Jorge Herrera Flores and María Patricia Velasco de León, revisited fossil specimens collected in the early 2000s using modern techniques such as computed tomography (CT) scanning. This approach allowed for a more accurate identification of the fossils, which were initially categorized as belonging to a species of Ambystoma.
By comparing the fossils with 13 living species of Ambystoma, including the endemic Xochimilco axolotl (Ambystoma mexicanum), the researchers established the distinctive characteristics of Ambystoma quetzalcoatli. Their findings highlight the evolutionary relationships between this new species and its living relatives.
Implications for Biodiversity and Evolution
The discovery emphasizes the importance of ancient ecosystems in shaping modern biodiversity. The researchers noted that Ambystoma quetzalcoatli exhibited neoteny, a trait allowing retention of juvenile characteristics into adulthood, which is prevalent in stable, isolated lake environments.
The study reinforces the concept that Mexico's current biodiversity has deep historical roots linked to ecosystems that have long since disappeared. UNAM stated, “The discovery of Ambystoma quetzalcoatli shows that the axolotl lineage has a much older evolutionary history than previously thought, with a presence in Mexico dating back to the Pliocene and an early diversification linked to ancient lake systems.”
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