Pseudoeurycea rex (Dunn 1921)

Pseudoeurycea rex shows sexual dimorphism, where females are larger than males. Males reach maturity at snout-vent lengths of 35 – 39 mm, and have an average adult snout-vent length of 46 mm. Females reach maturity at snout vent lengths of 42 – 50 mm and adults average 49 mm in snout-vent length (Houck 1977). The bluntly oval head is longer than wide. The snout is swollen and the nostrils are small. There is a tubercle below the nostrils. The diameter of the eye is longer than the distance from the snout to the eye. The eyelids fold under skin behind the eye. From the lateral view, the upper jaw appears slightly concave. There are teeth on the maxilla and nine vomerine teeth that extend beyond the nostrils. There are a total of 12 - 13 costal grooves. The limbs are well developed. When the legs are appressed, there are 2 – 4 costal grooves left exposed. The digits have minimal webbing at the base and are not very flat. The relative finger lengths are 3 > 2 > 4 > 1 and the toes are 3 > 4 > 2 > 5 > 1. The base of the circular tail is constricted and the tail itself is longer than the snout-vent length. The anal lips have palpillae (Dunn 1921). In life, individuals are dark with an almost black coloration, their dark coloration is likely to be a form of crypsis (Dodd Jr and Brodie Jr 1976). Dunn (1921) describes the species as having pinkish gray coloration on dorsum and dorsal surfaces of the limbs and tail, gray colorations on the lateral surfaces that is marbled with white, and light grey on the ventrum with white marbling on the throat and dorsal surface of the snout.The species authority is: Dunn, E.R. (1921). Two new Central American salamanders. Proc. Biol. Soc. Wash. 34, 143–145. The species was first named Oedipus rex by Emmett Reid Dunn in 1921. Blankers et al. (2012) preformed a large analysis using phylogenies from other studies, morphometric data, and microhabitat use. They showed that P. rex, P. exspectata, P. brunnata form a clade.

Pseudoeurycea rex is found in the Sierra de los Cuchumatanes in southwestern Guatemala. It occurs on Volcan Tacana on the border between Mexico and Guatamala. It can be found in altitudes from 2,450 to 4,000 meters above sea level, and it most commonly found higher than 2,800 meters above sea level (Acevedo et al. 2008).

Pseudoeurycea rex is fully terrestrial at higher elevations and can be found in leaf litter, under logs, and under moss mats. In cloud forests however, from 1,500 - 2,750 meters above sea level, individuals can commonly be found in bromeliads (Wake 1987). When found, individuals will most commonly stay still, using immobility to dissuade predators. When further threatened they will elevate and undulate their tails (Dodd Jr and Brodie Jr 1976). Pseudoeurycea rex is a terrestrial breeder with direct developing larvae (Houck 1977).

Pseudoeurycea rex was previously a very common species in Guatemala however in recent years there has been a significant decline in capture rates (Rovito et al. 2009). This decline coincides with the rise of the chytrid fungus, Batrachochytrium dendrobatidis (Bd), among Mexican amphibian populations (Cheng et al. 2011). Estimates made in 2011 show a 12% prevalence of chytrid in the species’ remaining populations (Cheng 2011).

Pseudoeurycea rex, which has been given the common name royal false brook salamander, is a species of salamander in the family Plethodontidae. It is found in western Guatemala; on Volcán Tacaná, its range extends to the Mexican side of the Guatemalan–Mexican border.