A member of the Asian group of fanged frogs, the new species was discovered a few decades ago by Indonesian researcher Djoko Iskandar, McGuire's colleague, and was thought to give direct birth to tadpoles, though the frog's mating and an actual birth had never been observed before.
"Almost all frogs in the world – more than 6,000 species - have external fertilisation, where the male grips the female in amplexus and releases sperm as the eggs are released by the female," McGuire said.
"But there are lots of weird modifications to this standard mode of mating. This new frog is one of only 10 or 12 species that has evolved internal fertilisation, and of those, it is the only one that gives birth to tadpoles as opposed to froglets or laying fertilised eggs," said McGuire.
Fanged frogs - so-called because of two fang-like projections from the lower jaw that are used in fighting – may have evolved into as many as 25 species on Sulawesi, though L larvaepartus is only the fourth to be formally described.
They range in size from 2-3 grams - the weight of a couple of paper clips - to 900 grams, or two pounds. L larvaepartus is in the 5-6 gram range, McGuire said.
The new species seems to prefer to give birth to tadpoles in small pools or seeps located away from streams, possibly to avoid the heftier fanged frogs hanging out around the stream. There is some evidence the males may also guard the tadpoles. The research was published in the journal PLOS ONE.