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.

Although frogs are predominately opportunistic carnivores, numerous studies report large amounts of plant material in anuran stomachs, citing accidental ingestion as the likely cause. Herein, we present evidence suggesting deliberate plant uptake in the Sabre-toothed Frog (Odontobatrachus ziama) and propose that this trait is specific to the entire family Odontobatrachidae. We performed stomach-flushing on 814 frogs, resulting in 665 dietary samples comprising all 5 Odontobatrachus species and two similar-sized, syntopic frogs, Astylosternus occidentalis and Conraua alleni. We collected dietary samples across the entire range of Odontobatrachus, in both wet and dry season. Additionally, we collected stomach contents of an O. ziama population during a 12-d capture–mark–recapture study in three different river habitats and compared the consumed and available plant material. We found that all Odontobatrachus spp. ingested the pinnate leaf of the riparian tree Parkia bicolor. These leaves were the most abundant food items in the stomachs of three out of the five Odontobatrachus species. Although mean proportional uptake of the leaflets did not differ seasonally, the maximum amount of leaflets was greater during the dry season, coinciding with peak leaflet availability. We found up to 100 single leaflets in stomachs of Odontobatrachus arndti, but syntopic Astylosternus and Conraua had ingested considerably smaller quantities of Parkia leaflets. Lastly, we found a greater prevalence of Parkia leaflets in females, with significant variation in leaflet uptake between stream microhabitats that could not be explained by the availability of the plant material. Consequently, we analyzed the dietary items for co-occurrences of plant material and preyed-upon animals that would support the hypothesis of an accidental uptake. However, we could not find biologically meaningful co-occurrences. Based on the combined results of stomach-flushing, availability of food items, absence of meaningful co-occurrences of plant with animal matter and feeding experiment, we concluded that leaflets were likely swallowed deliberately, but not eaten for energy demands. The reason for the deliberate ingestion of plant material across the genus Odontobatrachus so far remains unresolved.

Key words: Astylosternus occidentalis; Conraua alleni; Frog diet; Guinea; Herbivory; Parkia bicolor; Stomach-flushing

The holotype of Odontophrynus americanus collected by Alcide d'Orbigny in northern Patagonia, Argentina differs morphologically from the tetraploid frogs repeatedly assigned to this species and that are distributed from central Argentina and Uruguay to the north to Brazil and Paraguay (probably also Bolivia). Surprisingly, the external characteristics of the holotype match with the morphology of the adult syntype and specimens currently referred to as Odontophrynus occidentalis distributed in central, western, and southern Argentina. On the basis of resemblance in position, number, size, and shape of the glandular warts, we propose that O. americanus should be considered a senior synonym of O. occidentalis. Consequently, we realize that the tetraploid frogs currently called O. americanus were all too often misidentified under this name. After reviewing all the available names applicable to this tetraploid species, we recognize Hyperoodon asper described by Rodolfo A. Philippi as valid, resurrecting this nominal species within the genus Odontophrynus, with the designation of a neotype from Montevideo, Uruguay. We also propose that Ceratophrys argentina Philippi is a nomen dubium. To update the taxonomy of the genus Odontophrynus, we provide partial chresonymies, morphologic diagnoses, cytogenetic and bioacoustic characters, and geographic distribution maps for both O. americanus and O. asper.