The swamp exhibit concept and the seahorse railing are one of the few design elements carried over from the original Academy. The Africa hall and the pendulum are the other carry-overs.
@Onychorhynchus coronatus The building that the original alligator pit and railing were built in the early 20th century. The current building opened in 2008.
@Onychorhynchus coronatus This page says that the first iteration of the Steinhart Aquarium opened in 1923, so your design thoughts fit right in with that.
