Piotr wrote: 
 It's easy to find archaic features in ANY language, also in English: no merger of obstruent series; the unique survival of PIE *w; archaic lexemes like father (lost in Balto-Slavic!), etc. 
 
There's a hypothesis tha Slavic *batja:*bat'a:bata, despite some obvious difficulties, can be derived from *pHters>*pətēr.
 
Sergei