A dolphin, or perhaps a porpoise, has been spotted in the Thames near Richmond Bridge.

Bryon Dobson questioned which it was when he posted it on Facebook after his spot on Sunday (November 5) - so what do you thnk?

According to charity Whale and Dolphin Conservation (WDC) the biggest difference is size, with “all species of porpoise being much smaller than their dolphin cousins”.

The WDC webiste states: “Porpoises don't have the pronounced beak that most, but not all dolphins have and they also have a different teeth shape.

“Porpoise teeth are spade-shaped whilst dolphins are conical.

“A dolphin has a hooked or curved dorsal fin (except for those species that don't have a dorsal fin) whereas a porpoise has a more triangular dorsal fin, and generally speaking, dolphin bodies are leaner, whilst porpoises’ are a little more chunky.

“Dolphins are also more ‘talkative’ than porpoises.

“The whistles made by dolphins are produced through their blowholes and whilst porpoises do not do this, possibly due to structural differences in the porpoise’s blowhole, they can still be pretty noisy as they ‘puff’ the air out when they surface.”

Dolphins and porpoises also have a lot in common, one of which is their extreme intelligence.

Can you tell which it is?