I believe creatures with multiple primary attacks can use all their attacks in a round as a full-attack action. Otherwise if they make an attack as a standard action, they only get one of their attack types.
This is a difficult question and I had to do some searching and comparing. But I found another question on Stack Exchange where an answeran answer read as such:
"The creature with two claws and a bite can take three attacks on a full attack (the claw/claw/bite dating all the way back to at least 2e), or can move and still take one of the three as a standard action (almost every creature with both claws and bite will choose the bite if they only get one.) A max-sized dragon can attack with claw/claw/bite/wing/wing/tail with a full attack." (User: gatherer818gatherer818 )
Looking at the stat block for a Great Wyrm Red Dragon, its melee full-attack would look like: bite +37 (4d8+24/19-20), 2 claws +37 (4d6+16), 2 wings +35 (2d8+8), tail slap +35 (4d6+24). Notice by the bonus that both the bite and the claws are primary attacks, but can be used in the same round if the attack is a full-attack.