Tailed Frogs are considered to be (along with a handful of New Zealand frogs) the most primitive living frogs. The word "primitive" is somewhat misleading. It doesn't mean that these frogs are somehow "less evolved" than other frogs, since all living frogs have been evolving for the same span of time. What this really means is that all other types of living frogs are more closely related to each other than they are to Tailed Frogs and their New Zealand relatives.

Tailed Frogs don't actually have tails; the males have a copulatory organ approximately where a tail would be. The only one I've come across so far was a female, so there's no sign of a "tail" here.

Until recently, all tailed frogs were classified in this species, which was the only species in its genus, which is the only genus in its family. A few years ago the population of tailed frogs in the Rocky Mountains was reclassified as a separate species, the aptly-named Rocky Mountain Tailed Frog (Ascaphus montanus).

I returned to the same area in 2020 and spent quite a while looking for more of these frogs. Finally I saw one in the calm edges of a shallow stream, and a few minutes later a second, darker, one showed up. These two were about the same size as the one I had seen back in 2006, so I assumed that was the typical size of these frogs: about an inch long. While I was taking photos of the second one, a much much larger frog hopped past me and I realized it was the same species. I lost interest in the little frogs and spent a while chasing this three-inch hooligan around, waiting for it to pose nicely, which it soon did.