It's a dolphin. Sort of.

Believe it or not, this weird terracotta ornament is supposed to be a dolphin. Maybe you've see Neptune astride similar critters? I can only guess that people didn't see dolphins too often in classical times, and developed an unpleasant caricature of a dolphin in place of the actual, svelte version. The creepy, scaled version then entered the lexicon of architectural ornament.

This is from an apartment building on west side of Sheridan Road north of Greenleaf.