There was, indeed, an earlier lead-in to the show. It has Fred running errands through town, ending up at home grabbing his dinner from Wilma, and sitting down in front of the TV. I hadn’t seen it in years, but Cartoon Network runs it with the early episodes; I’m not sure why the other networks use the later opening for all the episodes.
There’s an early closing sequence as well, similar to the later ones, but towards the end the “camera” pans back and you see the lights come on, one by one, throughout Bedrock as Fred pounds on the door for Wilma to let him in.
As far as Dino goes, I’m surprised that he showed up in episode 6. It’s interesting that the website that you provided (well, not exactly, I had to pull back from the FAQ, then go into the “Flintstones” page) lists the recording dates for the episodes, and episode 11 (the snorkasaurus episode) has a question mark, meaning that it may have been recorded prior to episode 6.
On the other hand, I think it’s equally plausible that one of the artists simply added a “dog” in episode 6, without intending to make it a regular character, and then, after episode 11 was recorded, somebody decided that the “dog” was a good addition. There are numerous examples of characters being added for one show and then dropped and never mentioned again; the first one that comes to mind is Fluffy, the cat in the first Brady Bunch episode, but there are plenty of other examples as well. (Another one that comes to mind is Kitty Carry-all, also from The Brady Bunch, a doll that Cindy went everywhere with, but then was never seen with again after that episode. Then there’s Chuck in Happy Days.)
Unfortunately, if Cartoon Network is playing the episodes in order (I think they usually do), immediate research is not going to include episode 6, as they just played episode 9 (“Hot-lips Hannigan”) last night (10pm PDT). Hopefully the snorkasaurus will be on tomorrow night. . .
Rich