Was Buddha ever born as an elephant? I am not sure about this but the title of this book (When the Buddha Was an Elephant: 32 Animal Wisdom Tales from the Jataka) implies that Buddha was once an elephant; in other words that an elephant was a Buddha. 

Here is the story in question:





My question is: according to Jataka tales or other scriptural references, is it true that an elephant was a Buddha (not just Bodhisatta but Buddha)?
No. Animals can not become Buddha. 
Even if an elephant or any other animal regulates his life right ,he will not attain insight into the Truth.

To quote from Questions of King Milinda:


  'Venerable Nâgasena, those who regulate their lives aright--do they
  all attain to insight into the Truth, or are there some of them who do
  not?' 'Some do, O king, and some do not.' 'Then which do, Sir, and
  which do not?' 'He who is born as an animal, O king, even though he
  regulate his life aright, will not attain to insight into the Truth,
  nor he who is born in the Preta world, nor he who holds wrong views,
  nor the deceitful man, nor he who has slain his mother, or his father,
  or an Arahat, nor he who has raised up a schism in the Order, nor he
  who has shed a Buddha's blood, nor he who has furtively attached
  himself to the Order , nor he who has become a pervert , nor he who
  has violated a sister of the Order, nor he who, having been guilty of
  one or other of the thirteen grievous offences , has not been
  rehabilitated, nor a eunuch, nor an hermaphrodite--and whosoever is a
  human child under seven years of age, even though he regulate his life
  aright, will not attain to insight into the Truth. To these sixteen
  individuals there is no attainment of insight, O king, even though
  they regulate their life aright.'