Broadly speaking, the left-hand half is the older zoo and the right-hand the Quaternary Park extension, representing prehistoric wildlife of the region and tied in heavily with the nearby cave paintings at Altamira. I suspect there was some local goverment money available for this extension on this particular theme - it feels very different in concept to the rest of the zoo, but is equally cursed by lack of space. This is a zoo where most of the larger mammals are in enclosures that are at best adequate, and in many cases tiny. With Cabarceno just up the road, the contrast could scarcely be stronger. That's not to say Santillana is awful - but it would genuinely be better if it held two species of big cat, instead of four, and one great ape, instead of two, because there simply isn't the space, even for elderly, 'retired' animals, to do them justice.
