Reference for Chullin 205:30

בהמה בחייה לאברים עומדת ולא אתי איסור טרפה חייל אאיסור אבר

Alternatively, you may say, all agree that an animal [even] whilst alive stands to be dismembered into limbs, but in this case the animal was rendered trefah later on [and not at birth], and they differ whether or no the prohibition of trefah can be superimposed upon the prohibition of the limb [from a living creature].

Jastrow