WMG / Grand Unifying Guesses Hanna Barberaand Cartoon Cartoon

The classic Hanna Barbera shorts and the Cartoon Cartoons of the 90s/early 00s take place in the same universe during various points in time.

Here's a rough time line:

Human-kind develops Franklin Richards or Haruhi Suzumiya level reality warping through a result of genetic engineering and Hollywood Genetics. As a result, humans gain the ability to create living constructs with there minds (ie: imaginary friends). While people are capable of creating these entities throughout their lives, creating something like that is considered childish. As such creating these contructs end during early late childhood (with a brief reawakening during the teen years *the extremeasaurs*).

Hanna Barbera/Cartoon networks talking animals are imaginary friends. Friends who do not get adopted eventually establish their own community. They eventually rediscover time travel and arrive in various places in the past.