The axolotl was not recognized as a salamander until 1865, when several specimens at the Jardin des Plantes in Paris suddenly underwent metamorphosis. After some experimentation it was discovered that when their pools were dried up most of the animals changed into the adult form. Axolotls will also mature normally if fed thyroid gland extract. The related North American tiger salamander, A. tigrinum, often exhibits neoteny in the Rocky Mts., where the iodine content of the water is low. Since the late 1990s the axolotl has become increasingly endangered in its natural habitat due to pollution and competition from introduced fish.
The axolotl is classified in the phylum Chordata, subphylum Vertebrata, class Amphibia, order Urodela, family Ambystomidae.
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