They have scales and tails and fins and spiral up the lamp-posts. They also have nostrils and beaks and I think they are a Victorian representation of heraldic dolphins. The sculptures are dated, so I am confident in them being Victorian and, by this date (1870) books contained reasonably good representations of dolphins, so if the lamp makers had wanted to represent real dolphins they could have.
So, why are they here - what is their link to the British capital city and the river? Anyone know? I am confident there were once bottlenose dolphins in the Thames estuary but I suspect there is something more than that to these distinctive street adornments.