I came across this awhile ago and in my monster generator spreadsheet - rules are on the front page (on the vault - shameless plug) I have a set of rules and guildlines for calculating BMR - a lot of it drawn from discussion around the boards.
It covers humanoid, quadrupeds, wormers, flyers, gliders, multi legged and swimmers and also allows for fast and slow species.
I use it as it gives me a standard and reliable way to work out BMR .