Gayheart Talonthrust

Gayheart Talonthrust of Ankh is renowned among Swamp dragon breeders as the biggest known Swamp dragon ever, standing fourteen thumbs high, toe to matlock.

That might sound vaguely impressive until you convert that to more standard units- three foot six inches, or just over one meter.

As Sam Vimes learns in Guards! Guards!, Gayheart Talonthrust was considered a bit of a freak, as most male swamp dragons (cobbs) don't get bigger than 8 thumbs, or 2 feet. Female swamp dragons (hens) are a bit smaller. This proves beyond doubt that the giant Noble dragon attacking the city is definitely not a swamp dragon.