Scientists Have Identified a New Fossil Species of Axolotl in Mexico
Scientists Have Identified a New Fossil Species of Axolotl in Mexico
科学家在墨西哥发现了一种新的美西螈化石物种
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 in the state of Hidalgo. Named Ambystoma quetzalcoatli, it is the first fossil salamander species to be formally described in Mexico and the oldest known record of the genus Ambystoma ever documented in the country. According to the researchers, the discovery provides an important new piece of the puzzle for understanding the origin and evolution of the biodiversity that characterizes modern Mexican fauna.
墨西哥国立自治大学（UNAM）萨拉戈萨高等研究学院（FES Zaragoza）的研究人员在伊达尔戈州发现了一种新的美西螈（axolotl）化石物种。该物种被命名为 Ambystoma quetzalcoatli，这是墨西哥首个被正式描述的蝾螈化石物种，也是该国迄今为止记录到的最古老的钝口螈属（Ambystoma）化石。研究人员表示，这一发现为理解现代墨西哥动物群生物多样性的起源与演化提供了重要的新拼图。
The fossils were discovered in the municipality of Atotonilco el Grande, in Hidalgo, a region that was once home to an extensive freshwater lake system covering roughly 85 square kilometers. The lakes likely formed when the course of the Amajac River was temporarily blocked. This temperate, subhumid environment has yielded fossils of numerous plants, diatoms, gastropods, ostracods, beetles, and fish. Until now, however, the amphibian remains recovered from the site had never been formally studied or described.
这些化石是在伊达尔戈州的阿托托尼尔科埃尔格兰德（Atotonilco el Grande）市发现的。该地区曾拥有一个覆盖约85平方公里的广阔淡水湖泊系统，这些湖泊很可能是由于阿马哈克河（Amajac River）河道暂时受阻而形成的。这种温带半湿润环境出土了大量的植物、硅藻、腹足动物、介形虫、甲虫和鱼类化石。然而，此前在该地点发现的两栖动物遗骸从未被正式研究或描述过。
The researchers examined a dozen fossil salamander specimens collected in the early 2000s by the FES Zaragoza Paleobotany Research Group. Many of the fossils were exceptionally well preserved, with complete, articulated skeletons that allowed for a detailed anatomical analysis and a precise assessment of their morphology.
研究人员检查了由FES萨拉戈萨古植物学研究小组在21世纪初收集的十几件蝾螈化石标本。许多化石保存得异常完好，拥有完整且有关节连接的骨架，这使得研究人员能够进行详细的解剖学分析，并对其形态进行精确评估。
The remains were initially identified as belonging to a species of the genus Ambystoma, the group that includes modern axolotls. However, a team led by researchers Jorge Herrera Flores and María Patricia Velasco de León revisited the material using modern techniques, including computed tomography (CT) scanning and detailed anatomical comparisons with living species, to determine its identity more accurately.
这些遗骸最初被鉴定为属于钝口螈属（Ambystoma），该属包括现代的美西螈。然而，由豪尔赫·埃雷拉·弗洛雷斯（Jorge Herrera Flores）和玛丽亚·帕特里夏·贝拉斯科·德莱昂（María Patricia Velasco de León）领导的研究团队利用现代技术（包括计算机断层扫描（CT）和与现存物种的详细解剖学对比）重新研究了这些材料，以更准确地确定其身份。
Their analysis revealed that the fossils collected nearly three decades ago belonged to an entirely new species, distinguished from modern axolotls by several significant anatomical differences.
分析显示，这些近三十年前收集的化石属于一个全新的物种，它与现代美西螈在几个重要的解剖学特征上存在显著差异。
According to the study, published in Palaeontologia Electronica, the fossils display distinctive features of the skull and skeleton that are absent in living species. Among the most notable are an elongated opening on the top of the skull, a differently structured palate, variations in the arrangement of several cranial bones, and the presence of 17 trunk vertebrae. This last characteristic is particularly significant, as modern axolotls have 16 or fewer trunk vertebrae.
根据发表在《电子古生物学》（Palaeontologia Electronica）上的研究，这些化石展示了现存物种所不具备的独特颅骨和骨骼特征。其中最显著的是颅骨顶部有一个细长的开口、结构不同的腭部、几块颅骨排列方式的差异，以及拥有17块躯干椎骨。最后一个特征尤为重要，因为现代美西螈通常只有16块或更少的躯干椎骨。
To establish the fossils’ identity, the researchers compared them with 13 living Ambystoma species, including several endemic to Mexico, such as the Xochimilco axolotl (Ambystoma mexicanum), as well as tiger salamanders from Mexico and the United States. They relied on three-dimensional imaging and CT scans available through international scientific collections.
为了确定化石的身份，研究人员将其与13种现存的钝口螈属物种进行了比较，其中包括几种墨西哥特有物种，如墨西哥钝口螈（Ambystoma mexicanum），以及来自墨西哥和美国的虎纹钝口螈。他们利用了国际科学收藏库提供的三维成像和CT扫描数据。
To complement these comparisons, the team also obtained complete skeletons of the modern salamander Ambystoma velasci, using them as direct references to compare the shape and structure of living bones with those preserved in the fossils.
为了补充这些对比，研究团队还获得了现代蝾螈 Ambystoma velasci 的完整骨架，将其作为直接参考，对比现存骨骼与化石中保存的骨骼在形状和结构上的差异。
The scientists then investigated the evolutionary relationships between the fossil salamanders and their living relatives through a comparative analysis of skeletal characteristics, incorporating the results of previous DNA-based studies of modern salamanders.
随后，科学家通过对骨骼特征的比较分析，并结合此前基于现代蝾螈DNA的研究结果，调查了这些化石蝾螈与其现存亲属之间的演化关系。
Their findings indicate that, like living species such as the Xochimilco, Pátzcuaro, and Alchichica axolotls, Ambystoma quetzalcoatli exhibited neoteny—the biological trait that allows an animal to retain juvenile characteristics throughout adulthood.
研究结果表明，与索奇米尔科（Xochimilco）、帕茨夸罗（Pátzcuaro）和阿尔奇奇卡（Alchichica）美西螈等现存物种一样，Ambystoma quetzalcoatli 也表现出幼态持续（neoteny）现象——这是一种使动物在成年后仍保留幼体特征的生物学特性。
This adaptation typically evolves in stable, isolated lake environments, where there is little evolutionary pressure to undergo the complete metamorphosis seen in most other amphibians. The discovery suggests that this life-history strategy was already present in Mexican axolotls during the Pliocene, several million years ago.
这种适应性通常在稳定、孤立的湖泊环境中演化出来，因为在这些环境中，动物几乎没有演化压力去经历大多数其他两栖动物所表现出的完全变态发育。这一发现表明，这种生活史策略在数百万年前的上新世时期就已经存在于墨西哥的美西螈中。
At the same time, the anatomical and physiological characteristics identified by the researchers clearly showed that these fossils represent a previously unknown species. The discovery confirms that the evolutionary history of axolotls stretches much farther back than previously believed and that these amphibians have inhabited what is now Mexico for millions of years.
与此同时，研究人员确定的解剖和生理特征清楚地表明，这些化石代表了一个此前未知的物种。这一发现证实，美西螈的演化历史比此前认为的要久远得多，这些两栖动物在数百万年前就已经栖息在今天的墨西哥境内。
In a statement, 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. Beyond the identification of a new species, this discovery reinforces the idea that Mexico’s modern biodiversity has deep roots in ecosystems that disappeared millions of years ago.”
墨西哥国立自治大学在一份声明中表示：“Ambystoma quetzalcoatli 的发现表明，美西螈谱系的演化历史比之前认为的要古老得多，其在墨西哥的存在可以追溯到上新世，且早期的多样化与古代湖泊系统密切相关。除了鉴定出一个新物种外，这一发现还强化了一个观点：墨西哥现代的生物多样性在数百万年前消失的生态系统中有着深厚的根源。”