Hanna-Barbera/WMG
All the Hanna-Barbera shows take place in one universe.
On a trip to Europe, Dr. Quest discovered medieval texts telling of small blue creatures of human-like intellect. He eventually runs into a live specimen as well as a similar race of aquatic beings described in 17th century naval reports.
Using Smurf and Snork DNA, Dr. Quest creates intelligent talking animals by mixing DNA with various species. But many of the test subjects, such as Yogi Bear, Huckleberry Hound, Magilla Gorilla, Scooby Doo and Top Cat's gang escaped into the wilds or into the cities. As these animals grew more intelligent, some like Hong Kong Phooey, Quick Draw McGraw, Atom Ant and Secret Squirrel would help humans in keeping the peace as superheroes or secret-agents. Government genetic engineering efforts to create their own heroic talking animals, robots and superheroes ranging from Dynomutt to The Impossibles and Frankenstein Jr. met with mediocre success or just making things worse.
When The Valley Of The Dinosaurs was discovered in South America, the government rushed to create more intelligent creatures, though only resulting in rather docile prehistoric experiments. As things on the surface continued to get worse, humanity's elite bailed from the surface, ranging from going into towering ivory "magic sky castles", under the sea or into space. The people and intelligent animals, prehistoric and otherwise, that were left behind reverted to a more prehistoric culture that still resembled the lost ways, a modern Stone-Age if you will.
As humanity declined, the more human-like talking animals would create their own civilizations resembling those of humanity before the fall including Megakat City and an undersea city with the law being kept by Fish Police.
Laff-A-Lympics and Wacky Races confirm this for early Hanna-Barbera.