i think many salamanders usually has tails and frogs usually don't have tails

Your perception captures a general tendency in the biology of these two amphibian groups: 1. **Salamanders**: - Many salamanders, particularly those in their larval stage and certain species as adults (like various species within family Plethodontidae), indeed have tails. - As adults, tail presence can vary by species. For example, adults in some salamander families like Salamandridae (newts) often have reduced or no tails. However, some, like the waterdogs and mudpuppies in the family Proteidae, retain large, laterally compressed tails throughout their lives. 2. **Frogs**: - Adult frogs generally do not have tails. Their life cycle starts with tadpoles that have tails for swimming in water. As tadpoles go through metamorphosis into juvenile or adult frogs, they absorb their tails for energy, losing them completely in most species. The tail muscles are used to generate calcium stores in the body, which are then used in bone development. - Some frog species, specifically those more adapted to arboreal or climbing lifestyles, may develop thin, short projections from their backs which are not true tails and serve no similar function to those in salamanders. It's worth noting that the absence or presence of tails in adult amphibians largely relates to their habitat needs, mode of locomotion, and other evolutionary adaptations. Thus, while tails in salamanders may be quite common, there is significant variability in both groups reflecting the diverse evolutionary lineages within amphibians.