I agree with Jubal.
Historically, the North African Elephants were smaller than their Syrian and Indian counterparts. Gameplay wise, this would translate in a cheaper and weaker local elephant unit (North African Elephant), that, nevertheless, could give Carthago an edge in some battles, and in an imported bigger towered elephant unit, but also very costly (Syrian Elephant).
Hannibal's elephant was named Surus("the Syrian") so we can assume that Carthago had the possibility to import bigger elephants than the local ones. Moreover, many modern scholars consider that the North African Elephant was to small to be capable of carrying a tower in his back.