Meaning: Lions are not the fastest animal.
The English translation sounds strange to me.
I think that in this sentence, the word "animal" should be in plural form "animals".
Oddly, both sound correct, yet both sound incorrect to me. Think I must be having a brain fart. I think both should continue to be accepted.
"Lions are not the fastest animals" or "the lion is not the fastest animal" would be better, at least for my dialect.