saber-toothed tiger vs sabre-toothed tiger

saber-toothed tiger

noun
  • Any of numerous species of prehistoric cat-like mammals (principally in the subfamily Machairodontinae), characterized by massive, but short, legs and two large canine teeth, each about seven inches long and shaped like a saber. 

sabre-toothed tiger

noun
  • Any of numerous species of extinct cat-like mammals, of the Machairodontinae subfamily of the Felidae. 

How often have the words saber-toothed tiger and sabre-toothed tiger occurred in a corpus of books? (source: Google Ngram Viewer )