First known amphibian with a venomous bite

The first known amphibian with venomous jaw glands is the ringed caecilian (Siphonops annulatus), native to much of South America, including Brazil. In 2018, evolutionary biologist Dr Pedro Mailho-Fontana from the Butantan Institute in São Paulo, Brazil, discovered that this species possesses large glands in the upper and lower jaws with ducts going to the teeth. Optical and electron microscopical studies revealed these glands in several other caecilian species too, and showed that they arise from dental tissue, as do the venom glands in venomous snakes. Also, fluid secreted by the caecilian jaw glands contained certain enzymes frequently found in animal venoms. Moreover, after observing living specimens obtaining prey, in a 3 July 2020 scientific paper published in iScience, Mailho-Fontana and his team stated: "…secretion release seems to depend on prolonged bites [and] the presence of secretion covering the teeth surface during predation suggests that the teeth can inoculate secretion at the moment of the bite". In other words, it seems likely that these limbless, outwardly earthworm-like amphibians have a venomous bite. Most species are burrowers, living predominantly underground, but some are aquatic.

The discovery of these glands in caecilians and the strong likelihood that they therefore have a venomous bite are particularly noteworthy inasmuch as several such species have long been claimed to be venomous by local inhabitants. For example: in 1930, researcher Dr K Lafrentz had been digging through a pile of donkey dung on a coffee plantation in Mexico's Oaxaca State when suddenly a throng of blue-black caecilians emerged from it that proved to belong to a species new to science. Up to 45 cm long, it was formally named the Lafrentz caecilian (Dermophis oaxacae), but was already well known to the local indigenous people, who called it the metlapil, and claimed that it was venomous – a claim rejected by scientists back then.