The Craugastor mexicanus series (Anura: Craugastoridae) includes six species of direct-developing frogs that occur in Mexico and Guatemala. Notably, two of these species have small adult body sizes (<18 mm snout to vent length) and several have intraspecific polymorphism in color pattern. Using a geographic sampling focused on eastern Mexico (the location of most type localities), we conducted a molecular phylogenetic analysis of two mitochondrial (12S, 16S) and two nuclear (RAG1, TYR) gene fragments. This analysis revealed two widespread species, C. mexicanus and C. pygmaeus, along with evidence of multiple undescribed taxa from the states of Oaxaca, Mexico, Guerrero, and Jalisco. Interestingly, the widespread species have stratified geographic distributions with the larger bodied clade restricted to high elevations and the smaller bodied clade to low elevations. We also identify regions of Guerrero and Oaxaca where multiple species co-occur. To reevaluate the quality of characters that have been previously used to diagnose species, we tested for heterochrony and sexual dimorphism using microcomputed tomography and linear measurements. We found evidence for paedomorphosis as the mechanism of miniaturization in small-bodied taxa. Linear measurements confirmed that tympanum and body size are sexually dimorphic traits in both small- and large-bodied species. We used this enhanced understanding of morphological variation in the group to describe six new species. Despite this progress, we suspect that additional species await discovery, particularly in western Mexico and east of the Isthmus of Tehuantepec where our sampling efforts were limited.
KEYWORDS: Brachycephaloidea, Craugastor bitonium sp. nov, Craugastor candelariensis sp. nov, Craugastor cueyatl sp. nov, Craugastor polaclavus sp. nov, Craugastor portilloensis sp. nov, Craugastor rubinus sp. nov, Terraranae
Craugastor cueyatl sp. nov.
from Estado de Mexico.
Named with the word for frog in Nahuatl, an Aztec language that has been spoken in the Valley of Mexico since the 7th century, a region that includes the type locality of the species.
Craugastor polaclavus sp. nov.
The small (pola-) warty (-clavus) frog... because it's small and warty
Craugastor portilloensis sp. nov.
Mexico's smallest frog at only 11mm long. One of the smallest #frogs in the world!
Named after the town of Portillo del Rayo where the species is found.
Craugastor rubinus sp. nov.
The name is from the Latin for ruby, inspired by the garnet mines found near the type locality.
Tom J.M. Jameson, Jeffrey W. Streicher, Luigi Manuelli, Jason J. Head and Eric N. Smith. 2022. Miniaturization in Direct-Developing Frogs from Mexico with the Description of Six New Species. Herpetological Monographs. 36(1); 1-48. DOI: 10.1655/0733-1347-36.1.1
All these species are endemic to #Mexico and are part of the genus Craugastor, a group of terrestrial direct-developing frogs (no tadpoles, perfect miniature adults straight from the egg). These little fellas live in the leaf litter throughout the forests of Mexico.