In Pathfinder (and possibly 3.5, I’m not sure), Druids get an Animal Companion as a class feature. Rangers do as well, but their Druid level is equal to that of their Ranger level -3.
In D&D 5th Edition, Druids do not have an Animal Companion, only Rangers do.
What was the designers’ thinking behind dropping Animal Companions for Druids and making it only available to Rangers? Is there any dev commentary available on the reason for the change?
In an early interview about D&D Next (the playtest version of the game which led to D&D 5e), Mike Mearls made the following comment in response to a question about familiars:
Some people really like the feeling that a companion animal is a flesh and blood creature, but there are a lot of advantages to presenting it as a spirit companion or something similar.
It seems that this idea of a druid’s “spirit companion” has come through in the Unearthed Arcana supplement on Druids, for Circle of the Shepherd (Spirit Bond and Guardian Spirit).
Clearly the designers were thinking carefully about how to differentiate various kinds of animal companions, initially giving none to the druid, but then allowing a druid a spirit-type companion with the Unearthed Arcana update.