Continuity mistake: The cave bear tears the head off the man with the blue eyes. In the very next shot there is no trace of blood anywhere on the bear.
Continuity mistake: When the lion cuts Ayla's leg there are three cuts, however, when Isa finds her passed out, there are four cuts.
Continuity mistake: At the beginning of the movie when Ayla's mom is dying, Ayla grabs on to a finger or her outstretched hand. The scene cuts and Ayla's mom has her hand wrapped around Ayla's hand.
Factual error: The clan people look nothing like Neanderthals, they look like Cro-Magnon with a little dirt on.
Revealing mistake: When Ayla is looking at her "ugly" reflection in the lake she moves her hand down and a second later the reflection moves its hand down.
Revealing mistake: When Ayla gets her leg cut by the lion, the claw that cuts her doesn't look like a lion's paw (it looks like a bear) and you can see the "blood" is already on the paw and coming out of it as it dragged across her legs.
Continuity mistake: The C-shaped scar on the right chest of the man that likes Ayla changes shape between the time he is wrestling and the time he stops Ayla.
Continuity mistake: Near the beginning when the lioness growls at Ayla, and then darts after the child. Ayla runs into a cave. But in the next cut it's a lion digging the ground, trying to get at Ayla. (00:07:43)
Answer: The only reason I (and anyone I asked) could find was that, as usual, they discarded the ending though emotionally intense for the sake of another climax full of physical violence after the belief that this is the type of endings people prefer in the movies. Really sad indeed.