Part of it's text is a constant effect which states "This unit must be declared as an attacker or defender, if able."

Does this force the controlling player to declare every attack that he could? Such as he must attack a fulcrum AND must make an attack vs somebody's capital zone?

Curious as to the answer. Also, isn't there some other unit with a similar card text that this may also apply too?

I don't think effects like this can force you to declare an attack. If you don't declare the target of an attack (zone, legend, fulcrum) you immediately skip to the end of the battlefield phase. So there's no declare attackers step, and the Carnosaur doesn't get declared. It's more a "if you attack/defend, this guy has to participate" than a "you have to attack/defend". But the intention might have been different.

OK we'll go with the Mallumo ruling. Thank you sir.