# Ancient Salamander Fossils Unearthed in Hidalgo Push Back the Axolotl's Family Tree by Millions of Years

> Researchers in Mexico have described Ambystoma quetzalcoatli, the first fossil salamander species ever formally identified in the country and the oldest known fossil record of the axolotl genus Ambystoma, recovered from an ancient lake bed in Hidalgo.

**Type:** article · **Category:** Science · **Published:** 2026-07-04 · **Source:** TrendKia
**Canonical:** https://trendkia.com/en/science/mexico-ke-hidalgo-men-mila-lakhon-sala-purana-jivashma-eksolotala-ki-nai-prajati-ki-hui-pahachana-4659 · **Language:** English
**Tags:** Paleontology, Axolotl, Mexico, Hidalgo, New Species, Neoteny

Paleontologists in Mexico have described a previously unknown fossil salamander species, _Ambystoma quetzalcoatli_, marking the first time a fossil salamander has been formally described in the country and the oldest confirmed record of the genus _Ambystoma_, the group that includes today's axolotls, ever found there. Researchers say the find fills in a missing piece of how Mexico's present day biodiversity took shape.

## A Lost Lake System in Hidalgo
The fossils turned up in the municipality of Atotonilco el Grande, in the state of Hidalgo, a spot that once sat beside a sprawling freshwater lake system spread across roughly 85 square kilometers. Researchers believe the lakes formed after the Amajac River's course was temporarily blocked, creating a temperate, subhumid environment that trapped and preserved an unusually wide range of life. Over the years the site has produced fossils of plants, diatoms, gastropods, ostracods, beetles and fish. What it had not produced, until now, was a formal scientific description of its amphibian remains.

## Fossils Waiting Decades for a Second Look
The specimens at the center of the new study, a dozen fossil salamanders in total, were actually collected in the early 2000s by the FES Zaragoza Paleobotany Research Group. Many were remarkably well preserved, with complete, articulated skeletons detailed enough to allow for a full anatomical breakdown. At the time, the remains were tentatively filed under the genus _Ambystoma_, the group modern axolotls belong to. It took a fresh look, led by researchers Jorge Herrera Flores and María Patricia Velasco de León, using computed tomography (CT) scanning alongside close anatomical comparisons with living species, to work out exactly what the fossils represented.

## What Makes Ambystoma quetzalcoatli Different
That renewed analysis, published in the journal Palaeontologia Electronica, concluded that the nearly three decade old fossils actually belonged to a species science had never recorded. Several skull and skeletal features set it apart from any living axolotl: an elongated opening on the top of the skull, a differently shaped palate, a different arrangement of certain cranial bones, and, notably, 17 trunk vertebrae. That last detail matters because modern axolotls have 16 trunk vertebrae or fewer, making the vertebra count one of the clearest physical markers separating the fossil species from its living relatives.

## Comparing Bones Across 13 Living Species
To confirm the fossils' identity, the team lined them up against 13 living _Ambystoma_ species, among them axolotls endemic to Mexico such as the Xochimilco axolotl (_Ambystoma mexicanum_), as well as tiger salamanders found in both Mexico and the United States. The comparisons drew on three dimensional imaging and CT scans housed in international scientific collections. The researchers also obtained complete skeletons of the modern salamander _Ambystoma velasci_ to use as a direct physical reference point, comparing bone shape and structure against what had been preserved in the fossil material. From there, they mapped the evolutionary relationships between the fossil salamanders and their living relatives, cross checking skeletal comparisons against earlier DNA based studies of modern salamanders.

## A Trait Frozen in Time: Neoteny
One of the more striking findings is that _Ambystoma quetzalcoatli_ shared a trait with several living axolotls, including the Xochimilco, Pátzcuaro and Alchichica axolotls: neoteny, the biological quirk that lets an animal keep its juvenile features into adulthood instead of undergoing full metamorphosis. Neoteny tends to show up in stable, isolated lake environments, where there is little evolutionary pressure to push through the complete transformation most other amphibians go through. Finding it in this fossil suggests that Mexican axolotls were already living this way during the Pliocene, several million years ago, long before anyone was around to record it.

## Rewriting the Axolotl's Timeline
Taken together, the skeletal and physiological details convinced the researchers they were looking at a genuinely new species, one that pushes the known evolutionary history of axolotls back much further than scientists had previously assumed. It also confirms that these amphibians have been living in what is now Mexican territory for millions of years. In a statement, the National Autonomous University of Mexico (UNAM) said 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." The university added that beyond identifying a new species, the discovery "reinforces the idea that Mexico's modern biodiversity has deep roots in ecosystems that disappeared millions of years ago."

## What this means for you
- **For biology students and axolotl enthusiasts:** The find gives a clearer, deeper timeline of how the axolotl lineage evolved, which is useful for anyone studying Mexico's amphibians or involved in axolotl conservation, since living axolotl species today are considered endangered.

## Questions & Answers

### 1. Where was this new fossil species found?
It was found in the municipality of Atotonilco el Grande in the state of Hidalgo, Mexico, a site that once had a freshwater lake system spread across roughly 85 square kilometers.

### 2. Why is this discovery considered significant?
It is the first fossil salamander species ever formally described in Mexico and the oldest known fossil record of the genus Ambystoma in the country.

### 3. How is Ambystoma quetzalcoatli different from living axolotls?
It has an elongated opening on top of the skull, a differently structured palate, and 17 trunk vertebrae, while modern axolotls have 16 trunk vertebrae or fewer.

### 4. When were the fossils collected and who studied them?
The fossils were collected in the early 2000s by the FES Zaragoza Paleobotany Research Group, and the new analysis was led by researchers Jorge Herrera Flores and María Patricia Velasco de León.

### 5. Did this fossil species also show neoteny like modern axolotls?
Yes, like the Xochimilco, Pátzcuaro and Alchichica axolotls, Ambystoma quetzalcoatli exhibited neoteny, retaining juvenile characteristics into adulthood.

### 6. Where was the study published?
The study was published in the journal Palaeontologia Electronica.

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