Ainsworth’s salamander

Last seen in 1964: Plethodon ainsworthi, sp. nov.

Ainsworth’s salamander is known only from two specimens collected by biologist Jackson Harold Ainsworth in 1964, two miles south of Bay Springs in Jasper County, Mississippi. Ainsworth initially assumed that these individuals were Northern slimy salamanders (Plethodon glutinosus). However, more than 30 years later, American herpetologist James Lazell described the salamanders found by Ainsworth as a new species, P. ainsworthi.

From Lazell’s original scientific description in 1998, it is noted that Ainsworth’s salamander was black-brown with no distinctive patterning. The ventral side of the slender animal was light gray-brown. The type specimens had a total length of about 5.2 and 5.7 centimeters.

Despite intensive searches in 1991, 1995, and 1997, Ainsworth’s salamander, which belongs to the genus of woodland salamanders (Plethodon), could not be relocated. Consequently, the International Union for Conservation of Nature (IUCN) declared it extinct in 2004.

The IUCN considers increasing deforestation and the consequent loss of habitat as reasons for the species’ disappearance. Soil erosion and the drying up of springs could also have contributed to the extinction of Ainsworth’s salamander. As an amphibian, it inhabited both terrestrial areas and freshwater.

The IUCN lists Ainsworth’s salamander as the only extinct amphibian in the USA. Additionally, the Jalpa false brook salamander, endemic to Guatemala, disappeared in the 1980s, and the El Empalme worm salamander (Oedipina paucidentata) from the island of Costa Rica was last seen in 1952.

Ainsworth’s salamander – Fact sheet

Alternative name	Bay Springs salamander
Scientific name	Plethodon ainsworthi
Original range	Mississippi (USA)
Date of extinction	about 1964
Causes of extinction	habitat loss, soil erosion, drying out of springs

Ainsworth’s salamander: Extinct, extant, or nonexistent?

The failure to locate Ainsworth’s salamander despite multiple search efforts may not necessarily indicate the extinction of the species. Biologists John G. Hilmes and David C. Beckett also visited the site in 2000 and 2001 where Jackson Harold Ainsworth found two individuals in 1964. There, they encountered numerous Mississippi slimy salamanders (Plethodon mississippi), but no Ainsworth’s salamanders.

In a study published in the Southeastern Naturalist in 2013, Hilmes and Beckett explore whether Ainsworth’s salamander is a valid species. They suspect that Plethodon ainsworthi might be a junior synonym for the syntopic Plethodon mississippi, also known as the Mississippi slimy salamander.

Hilmes and Beckett propose that the original description of Ainsworth’s salamander by Lazell might have been influenced by the fact that the type and paratype had likely been stored in strong formalin for about 26 years before their identification in 1998, leading to their poor condition.

According to Lazell’s original description, Ainsworth’s salamander was supposed to differ from the Mississippi slimy salamander by having shorter limbs and a noticeably slimmer body. However, Hilmes and Beckett view these supposed differences as results of long-term, improper preservation of the specimens, leading them to suspect that Ainsworth’s salamander might not be a distinct species after all.

Conservation damage: Distinctive features hard to discern

Of the two specimens of Ainsworth’s salamander, already damaged by preservation, only the holotype remains today. It has broken into several pieces due to the strong formalin. The left forelimb, the tail end, all toes on the hind legs, and the first toe on the right forelimb have broken off.

The paratype was severely damaged and almost destroyed during a vertebral bone examination. The bones were completely decalcified due to prolonged immersion in formalin. However, the specimen was photographed and analyzed before the unsuccessful examination.

In 2020, herpetologist Todd W. Pierson and his colleagues presented a study in the Journal of Herpetology on morphological changes in salamanders caused by preservation. They examined the impact of preservation methods on morphological measurements. The results of their study cast doubt on the hypothesis by Hilmes and Beckett that the Ainsworth’s salamander specimens are actually poorly preserved Mississippi slimy salamander specimens.

Pierson’s attempts to extract DNA from the decades-old Ainsworth’s salamander holotype were unsuccessful, thus he could not disprove the opposite. Moreover, the demineralization of the Ainsworth’s salamander skeleton makes skeletal comparisons impossible. Pierson and his colleagues ultimately recommend continuing to recognize Plethodon ainsworthi as a valid, though likely extinct, species.