I guess that might fit - you can make out a couple of iguanas on the right hand side of the photo. (I've never been inside the Shedd Aquarium, so I'm just going on your photos)
According to this, they're Exuma Island Rock Iguanas. Last time I visited, March?, the entire signage above stated that this off use for the preparation of marine iguanas
Not really naturalistic for the species, but an ok exhibit anyway.
I've not been recently, but it's possible that they now exhibit Exuma Island iguanas after they received two recently (confiscated from smugglers). The species they've had historically is Grand Cayman blue as mentioned by snowleopard. Don't know if they could be mixed, but in general the West Indian iguanas are closely related and potentially can hybridize.
I'm sure they wish for marine iguanas and that might have been the idea when this exhibit was built. The chance of them actually getting marine iguanas in the future is about as large as getting platypus...
