The Rana temporaria is, well, basically the common frog. Its other names include the European Common Frog, the European Common Brown Frog and the European Grass Frog. It’s like the world just didn’t want these little guys to be special. However, the Internet Of Truths tells me that the Common Frog isn’t that common in Spain, home of this stamp. Despite living across most of Europe, from Ireland, to Scandinavia, to the Urals, the common frog doesn’t seem to live in the Iberian peninsula, viz Spain and Portugal.
The other name on the stamp is Rana Roja, which readily translates as red frog. This appears to be a very different specimen – a poisonous frog living in Central America (or a somewhat disappointing tourist lodge in Costa Rica, depending which link you follow).