Thread:KillerZ/@comment-2607:FB90:4A21:9CF:C4DF:C6DC:44AB:DE4A-20200206005010/@comment-1967967-20200206010058

I don't know. Probably lack of research. They did get few things wrong in the older games, like: Aztec calendar in Peru, Some of the animals appear in regions they shouldn't be, etc...

Looking at the T-Rex wikipedia article, there is a diagram of the hand, and it has the third bone there, a small metacarpal, maybe they though that bone also belonged to a separate finger.

But, this is only a speculation, only the creators would know for certain.